Assessment and optimization of felt living walls in terms of water retention performance and artificial lighting

University of Seville Higher Technical School of Agronomic Engineering Interuniversity Doctoral program in Agrarian, Food, Forestry and Rural Development Engineering Research line: Plant production technology DOCTORAL THESIS “Assessment and optimization of felt living walls in terms of water retention performance and artificial lighting” Author: Maria Pinelopi Kaltsidi Directors: Dr. Rafael Fernández Cañero y Dr. Luis Pérez Urrestarazu Tutor: Dr. Luis Pérez Urrestarazu Seville 2020 Universidad de Sevilla Escuela Técnica Superior de Ingeniería Agronómica Programa de Doctorado Interuniversitario en Ingeniería Agraria, Alimentaria, Forestal y del Desarrollo Rural Línea de investigación: Tecnología de la producción vegetal TESIS DOCTORAL “Estudio y optimización de la retención de agua y la iluminación artificial en jardines verticales textiles” Autor: Maria Pinelopi Kaltsidi Directores: Dr. Rafael Fernández Cañero y Dr. Luis Pérez Urrestarazu Tutor: Dr. Luis Pérez Urrestarazu Sevilla 2020 University of Seville Higher Technical School of Agronomic Engineering Interuniversity Doctoral program in Agrarian, Food, Forestry and Rural Development Engineering Research line: Plant production technology Doctoral student: Maria Pinelopi Kaltsidi Dr. Luis Pérez Urrestarazu and Dr. Rafael Fernández Cañero, supervisors of this Thesis, certify that it is ready to be presented. Seville, 2020 Supervisors' signature Dr. Luis Pérez Urrestarazu Dr. Rafael Fernandez Cañero University of Seville Higher Technical School of Agronomic Engineering Interuniversity Doctoral program in Agrarian, Food, Forestry and Rural Development Engineering Research line: Plant production technology DOCTORAL THESIS TITLE: “Assessment and optimization of felt living walls in terms of water retention performance and artificial lighting” Author: Maria Pinelopi Kaltsidi The current doctoral thesis meets the requirement established by the University of Seville for its presentation as a compendium of articles, consisting of a minimum of two articles published in scientific journals included in the first three quartiles of the list of journals in the field of specialty and referenced in the latest data published by the Journal Citations Report (JCR): Kaltsidi Maria Pinelopi, FernándezCañero Rafael, FrancoSalas Antonio, PérezUrrestarazu Luis, 2020. Improving the performance of feltbased living wall systems in terms of irrigation management in Urban Forestry & Urban Greening, Volume 54, Page 126782, Published by Elsevier, DOI: 10.1016/j.ufug.2020.126782, ISSN: 16108167, URL: https://doi.org/10.1016/j.ufug.2020.126782 JCR in 2019: Impact Factor: 4,021, Source Normalized Impact per Paper (SNIP): 1.561, SCImago Journal Rank (SJR): 1.181 and 1st quartile in the thematic area of Forestry. Kaltsidi Maria Pinelopi, FernándezCañero Rafael, PérezUrrestarazu Luis, 2020. Assessment of different LED lighting systems for indoor living walls in Scientia Horticulturae, Volume 272, Page 109522, Published by Elsevier, DOI: 10.1016/j.scienta.2020.109522, ISSN: 03044238, URL: https://doi.org/10.1016/j.scienta.2020.109522 JCR in 2019: Impact Factor: 2.769, SNIP: 1.626, SJR: 0.838 and 1st quartile in the thematic area of Horticulture Seville 2020 Acknowledgments I would like to express my sincere thanks to my supervisors Dr. Luis Pérez Urrestarazu and Dr. Rafael Fernández Cañero for the opportunity they offered me to work with them. I am grateful for their continued guidance, advice, effective decisions and assistance in completing my Ph.D. studies. The quick response and efficiency of Dr. Luis Pérez Urrestarazu played an important role in achieving all the goals set from the initiation of my studies. Apart from professors and brilliant scientists, I appreciated them even more as people who were by my side with understanding during the difficult period of the pandemic and the lockdown. I would also like to thank Dr. Vivian Loges with whom we worked on the realization of the virtual stay who always faces difficulties with her positive thinking and smile. In addition, I would like to thank Dr. Antonio Franco Salas who offered the space where the first experiment was carried out and his total help during both studies. Many thanks to David Sevillano, Patricio Espinosa and Ángela Morales, who helped me with the maintenance of the living wall modules and the measurements during the second study. Many thanks to my friend Christina for her support and help; nothing would be the same without her. I would like to thank Simón, my life partner, who never left my side, and without his wisdom, I couldn't see the hidden beauty in the difficulties. Finally, I profoundly thank my beloved parents Flora and Stathis, and my little brother, Iraklis, who supported me in every single step of my lifeeven if they knew that I will be far from them. You are the reason I have wings and I can fly. Doctoral thesis. Maria P. Kaltsidi 5 materiales utilizados en los sistemas de muros vegetales basados en fieltro para contribuir a la mejora de la gestión del agua con un enfoque sostenible, (b) la importancia de la implementación de programas de riego adecuados y (c) la limitada investigación desarrollada en este campo específico. Específicamente, el sistema Fytotextile con una manta de fibra de polímero muy absorbente (Fytotextile 4) y un geotextil de 4 mm de espesor, demostró una mayor capacidad para almacenar agua de riego en comparación con los otros tres sistemas Fytotextile. El Fytotextile con geotextil de 4 mm de espesor (Fytotextile 2) produjo el menor volumen de drenaje para todas las programaciones de riego. Por otro lado, las tres especies testadas (Erodium x variabile 'Roseum', Carex oshimensis 'Evergold', Lavandula dentata) funcionaron correctamente en todos los tipos de Fytotextiles, manteniendo un resultado estético elevado a corto plazo. Erodium x variabile 'Roseum' presentó el comportamiento más satisfactorio en todos los sistemas de Fytotextile mientras que para Lavandula dentata fue más deficiente. Finalmente, se sugiere la construcción de jardines verticales con materiales adecuados y testados, que puedan constituir sistemas de larga duración, que minimicen el uso de agua y materiales (por ejemplo, vegetación, geotextiles) para que sean eficientes en la obtención de los resultados deseados. En el segundo estudio, titulado “Assessment of different LED lighting systems for indoor living walls” y publicado en la revista Scientia Horticulturae, seis lámparas comerciales de diodos emisores de luz (LED) (Aster y Dahlia de Ignia Green, Logar CMH, CLH y Forum de Lledó, CFUT01 de Panda Grow), comúnmente usadas para instalaciones interiores, fueron evaluadas para determinar su idoneidad y eficiencia en el comportamiento de los sistemas de jardinería vertical. CFUT01 fue el único proyector específicamente diseñado para el crecimiento de plantas. La evaluación de la iluminación se basó en el patrón de iluminación, el consumo de agua, la temperatura generada y el efecto sobre el comportamiento de la vegetación, junto con la percepción de los observadores de la calidad visual de la luz. Específicamente, se llevaron a cabo dos estudios en interiores, completamente protegidos de la exposición al sol, utilizando el sistema Fytotextile®, y dos tipos de plantas de uso común en interiores (Soleirolia soleirolii y Spathiphyllum wallisii). De acuerdo con los resultados de este estudio, se pudo determinar que la iluminancia (como flujo luminoso por unidad de área) y el PPFD Doctoral thesis. Maria P. Kaltsidi 6 estaban correlacionados positivamente con la altura del módulo para cada bolsillo. La lámpara Logar CLH Superflood presentó el valor más alto para ambos rasgos, mientras que los valores más bajos se atribuyeron a la lámpara CFUT01. El jardín vertical que recibió la iluminación de Dahlia exhibió el consumo de agua medio diario más elevado, y Logar CMH Superflood el más bajo. El proyector CFUT01 fue el único que demostró no ser adecuado para jardines interiores. Aster y Logar CMH Superflood tuvieron un comportamiento deficiente cuando se colocaron más lejos del módulo, y Dahlia fue la que recibió una mayor calificación entre los encuestados. Finalmente, se puede destacar que parámetros como la distancia del proyector a la infraestructura del jardín vertical, su orientación, ángulo de haz, consumo de energía y la calidad visual también deben tenerse en cuenta al evaluar la eficiencia de los sistemas de iluminación. Doctoral thesis. Maria P. Kaltsidi 7 1. Introduction 1.1. Urbanization and vertical greening systems An elevated percentage of the words’ population lives in urban areas and according to United Nations Department of Economic and Social Affairs (UN DESA, 2018) in 2018 this percentage reached 55% and it is expected to increase to 68% by 2050. In this continuous urbanization, the key factor for the successful development of urban growth is the sustainable approach. Referring to a sustainable approach that leads to a better quality of urban life, one of the challenges to be faced is the enrichment of the urban areas with green spaces. The development of urban forests, community gardens, natural meadows, wetlands, increased number of trees and shrubs, parks and landscaped streets, squares, green roofs, and vertical greening systems profoundly ameliorates the appearance and the environmental quality (e.g. biodiversity) of urban areas. According to Lynne M. Westphal (2003) green spaces can improve the quality of life with their impact on social issues such as health care, education, crime and economic development. The conceptualization of increasing green spaces areas and reforming the densely built urban environment led to the evolution of applied technologies such as green roofs and vertical greening systems which allowed using the surface of the buildings to locate vegetation. However, the vertical greening systems are frequently subjected to criticism regarding their maintenance, installation and maintenance cost and the environmental sustainability focusing on the materials and the water usage (Manso and Castro-Gomes, 2015; Riley, 2017). It is difficult to determine the origin of the vertical greening systems however there are literary references, fabrics and works of art that allow us to hypothesize their existence. A first reference that may combine green roofs and potential green facades (hanging plants) could be found in the Hanging Gardens of Babylon, one of the seven wonders of the ancient world, even if their existence is questionable. There are important documentary sources that could certify their existence such as Ktisias` (late 5thearly 4th century BC) book “Persian” ("Περσικά") and Strabo` (64 BC24 BC) book “The Geography of Strabo” (“Η Γεωγραφία του Στράβωνα”) and Plutarch (45-120 AD) in “Parallel Lives” ("Βίοι Παράλληλοι") (Sikeliotis, 1396; Curtius, 1932). Later, various Doctoral thesis. Maria P. Kaltsidi 8 civilizations worldwide used climbing plants to cover buildings or facades. According to Pérez-Urrestarazu et al. (2015) living walls were potentially inspired by the epiphytic plant growth in the tropical forests and Hopkins and Goodwin (2011) mentioned that one of the main reasons living wall systems begun to develop was the need for shade in extreme climatic conditions in combination with aesthetically pleasing vegetation performance. Nowadays, Patrick Blanc, a French botanist, is considered the modern innovator of the living wall systems, initially named “Mur Végétal” (hydroponic felt system). 1.2. Types of living wall systems Given the fact the living wall systems are a rapidly evolving technology currently on the rise, classification is not a common ground among scientists and marketing stakeholders (Loh, 2008; Manso and Castro-Gomes, 2015; Medl et al., 2017; Ascione et al., 2020). Living walls also referred to as green walls or even vertical gardens are advanced systems enveloping buildings or facades (slightly inclined or not) indoors or outdoors characterized by vegetation with the root system integrated in the vertical system (Loh, 2008; Pérez-Urrestarazu et al., 2015; Medl et al., 2017). The materials of the surfaces where living walls are fixed vary among concrete, concrete masonry unit (CMU), wood or metal frames or even structural steel. Based on the application method living walls can be classified into continuous (light and permeable layers planted in situ e.g. geotextile, polyamide) or modular (various elements with specific dimensions, frequently preplanted) connected to the buildings´ walls by means of a substructure (e.g. galvanized stainless steel, timber) or even directly fixed (Manso and Castro-Gomes, 2015). Living walls may as well be divided into two main categories depending on the material used (Fig. 1), namely felt or cloth systems (Fytotextile by Terapia Urbana, ipanel by Verdtical, Mur Végétal by Patrick Blanc, Pocket Panels Florafert), and boxes or panel (e.g. Biotexture, Ansglobal, Sagegreenlife, Mobilane, Sempergreen) planted in situ or even frequently preplanted. However, commercially there are several subcategories promoted as living walls (e.g. gsky, NextGen, DIY modular units by Planter Designs, Botanicus, Windowbox, Mobilane, Maruja Fuentes Fuse Nature & Décor, Mercury Mosaics). Doctoral thesis. Maria P. Kaltsidi 9 Felt or cloth systems, can be continuous or modular and consist of flexible multilayer connected to a substructure fixed on a supporting wall. The various layers allow the aeration of the roots, the distribution of the irrigation water and the prevention of moisture problems in the supporting wall (waterproof layer). The plants may be housed in pockets with the initial potted growing medium (semihydroponic systems) or can be placed bare rooted directly into individual cuttings of the layers (hydroponic system) while additional nutrients are distributed through the irrigation system. The boxes or panel systems are modular, mainly not flexible systems which consist of materials such as rockwool blocks, coco fiber blocks, rock fiber, sphagnum, where plants are housed in specified cavities. In most of the cases, the blocks are preplanted maintaining the initial pot substrate and fixed on the structural system in situ with an irrigation system installed (Loh, 2008). Figure 1. Examples of different living wall systems; left a felt or cloth system and right a panel or box system (figure by Maria Pinelopi Kaltsidi) Doctoral thesis. Maria P. Kaltsidi 10 Some authors mention some subcategories that are considered to belong to the category of modular living wall systems and consist of containers, and/or trellis system, trays, vessels, planter tiles (Loh, 2008; Manso and Castro-Gomes, 2015). In these systems, plants are grown in containers or placed directly with the pot into the system and in some cases climb onto trellises. 1.3. Benefits and barriers of indoor and outdoor living wall systems Both outdoor and indoor living wall systems present considerable advantages that drive their ongoing rise as a novel approach to urban greening. According to our knowledge of the existing literature (Loh, 2008; Ottelé et al., 2010; Perini et al., 2011a; b, 2017; Coma et al., 2017; Medl et al., 2017; Ascione et al., 2020), living walls have been found to: • lower energy consumption of the building and, therefore, greenhouse gas emissions • increase the thermal performance of buildings, thus lowering energy costs • reduce the Urban Heat Island (UHI) effect • have a beneficial effect on hydrology and improve Water Sensitive Urban Design (WSUD) • improve air quality by filtering particles • reduce noise pollution • increase urban biodiversity and urban food production • improve health and wellbeing (biophilia) However, the vast implementation of living wall systems faces several barriers, at least regarding the current development of this technology. The major drawbacks of living walls can be summarized as follows (Ottelé et al., 2011; Perini et al., 2011b; Manso and Castro-Gomes, 2015; Ascione et al., 2020): • high investment/ installation cost • complex implementation that demands highlytrained personnel for the design and installation • high maintenance cost due to the need for frequent maintenance Doctoral thesis. Maria P. Kaltsidi 11 • in some cases, high water and nutrients consumption that may increase the environmental burden of some materials • unavailability of a shared constructive standard • difficult understanding of not uniform experimental results • absence of tested and certified commercial simulation models Though the aforementioned assets and liabilities are common to all living wall systems, their intensity varies among the different types and also in reference to distinct technical and/ or vegetation traits (Mårtensson et al., 2014; Pérez-Urrestarazu et al., 2014; Lausen et al., 2020). Such variability highlights the imperative need of careful and detailed design of living wall systems in order to accomplish the desired outcome, while it also pinpoints the need for further research on the multivariate response of living wall systems under different conditions. The specific characteristics of each living wall type give rise to distinct advantages and disadvantages (Perini et al., 2011b; Manso and Castro-Gomes, 2015). Continuous systems offer higher plant growth and water/ nutrients distribution uniformity, while, in modular systems, the size of the module represents a barrier. Moreover, continuous systems are a lightweight option when compared to modular systems that are generally heavier. On the contrary, modular systems can be easily disassembled when needed for maintenance purposes and they also allow a higher control over irrigation, nutrition and drainage. It is worth mentioning that while common to both outdoor and indoor living wall systems, the needs for irrigation and lightning present different peculiarities. Therefore, water management can be more challenging in the case of outdoor living walls, which are further exposed to changing and difficult to control environmental factors. On the other hand, the lighting requirements of indoor living wall systems, often located in places characterized by low exposure or even absence of natural light, make the use of artificial lighting systems necessary. Doctoral thesis. Maria P. Kaltsidi 12 1.4. Water management of living wall systems 1.4.1. Water requirements Water is an essential factor to ensure plant survival and robust growth, thus water management is of utmost importance when designing and maintaining any vegetation system. However, fulfilling the water requirements of a living wall can be more complex due to the particular characteristics of the specific system. Indoor living walls cover exclusively their water needs by means of irrigation in a relatively stable environment (room temperature, stable relative humidity, illumination). However, irrigation for outdoor living wall systems needs to be carefully programmed taking into account the microclimatic conditions that vary during the year and the location (precipitation events, hours of direct sunlight, exposure, relative humidity, average, max. and min. temperature). In general, the diverse outdoor living wall systems present little or none horizontal area where water could be stored, thus plants can use solely the amount of water retained by the substrate and/ or the porous supporting structure (Pérez-Urrestarazu et al., 2019). Along with the location of a living wall (indoors or outdoors and its orientation) and the climatic conditions, the plant selection and the substrate employed affect water needs and irrigation requirements. The plant palette of a living wall may consist of plants that prefer well or poorly drained, constantly moist or not, growing medium. On the other hand, apart from the synthetic material used on living wall, the composition of the growing medium such us peat, coconut coir, perlite, rockwool etc. affects the frequency and the duration of an irrigation program. An additional fact that should be taken into consideration when estimating water requirements is that the plants are cultivated for their ornamental and aesthetic value. Therefore, irrigation should be designed in order to reassure the healthy appearance of the vegetation and coverage of the wall, not prioritizing biomass production, as it is the case for most cultivated plants. An unsuccessfully designed irrigation programming may lead to significant water waste and antienvironmental, nonecological and unsustainable approach, as well as an elevated cost due to high maintenance demands Doctoral thesis. Maria P. Kaltsidi 13 (frequent inspection and maintenance visits, increased labor hours, plant pruning or replacement, substrate filling, high susceptibility to pests and diseases). 1.4.2. Irrigation systems Each type of living wall system dictates the design and application of distinct irrigations systems that will reassure a robust water management specifically adapted to the specific features of each living wall type. However, apart from their differences, the majority of the irrigation systems (built in or not) used for living walls have as common trait their high dependence from gravity (Pérez-Urrestarazu et al., 2019), thus demanding more complex solutions in order to mitigate water losses due to runoff and percolation and to achieve a uniform water distribution along the living wall. An appropriate irrigation guarantees an adequate homogeneous water supply and nutrients (fertirrigation) to the entire surface of each system and their availability to the plants. There are two irrigation designs for living walls, namely recycled/ recirculating and runtowaste. The recycled solution consists of a closed circuit connected to a tank where runoff from the irrigation events is collected at the bottom of the living wall and reused. A runtowaste system, usually recommended for small and medium sized living walls, is connected to a water supply and the excess of water goes directly to the drain so the irrigation water is used solely once. The most common irrigation system in the different living wall types is the drip irrigation (Fig. 2). Drip emitters or drippers are normally inserted directly to the mainline or through thinner tubing using a straight connector at its base. Pressurecompensating emitters are suggested due to their capacity to deliver a precise amount of water even in the change of water pressure, though it depends on the water flow (4, 2, 1.5 L h-1). The drip emitters release water to the upper level and at different levels depending on the size of the living wall. Therefore, the water can move vertically downwards due to the gravity and laterally between lines by diffusion (Pérez-Urrestarazu et al., 2014). Doctoral thesis. Maria P. Kaltsidi 14 Figure 2. Drip irrigation system example with driplines placed on the top of each module of the feltbased Fytotextile system (Photo courtesy of Terapia Urabana L.S., image modified by Maria Pinelopi Kaltsidi) There are more irrigation systems less frequently applied, such as exudative irrigation systems which can be used in small sized living. They consist of tubes which exude water through the tiny pores of the textile porous pipe and produce a continuous and uniform strip of moisture along the irrigation lines. Moreover, there are systems where plants receive water and nutrients through the capillary action when the cloth comes in contact with the irrigation water and the roots intertwine with the cloth. Another irrigation system is applied, in the case of trays, where the irrigation water is collected in the trays with the located potted plants and the substrate absorbs the water from the openings of the bottom of the pot and overflow drain to the tray below. Drainage lines can be connected directly to the trays assuring neat and spotless foliage. Doctoral thesis. Maria P. Kaltsidi 21 Aquaten used in Fytotextile 3. Fytotextiles 1 (original patent) and 2 which only consisted of geotextiles of different thickness presented the lowest water retention capacity. The drainage test, organized in 7 irrigation schedules (S1 to S7) combining 4 different durations (5, 10, 20, 40 min) and 5 different frequencies (1, 2, 4, 8 events d-1) (AppendicesPublication 1Table 2), revealed that in all cases Fytotextile 1 produced the highest drainage volume followed by Fytotextile 4, and Fytotextile 3, while Fytotextile 2 produced the smallest drainage volume (AppendicesPublication 1Table 3). However, the four tested Fytotextile systems presented similar patterns in the evolution of the average drainage water volume during a day (AppendicesPublication 1Fig. 5). The main differences appeared in schedules 1, 2 and 5 (S1, S2, S5) with higher frequencies applied (8, 4, 4 events d-1, respectively). Finally the three plant types used for the vegetation performance test, Erodium x variabile 'Roseum', Lavandula dentate, Carex oshimensis 'Evergold', with a trailing, bushy and tufted habit, respectively, exhibited high survival and a satisfactory performance in terms of aesthetics (AppendicesPublication 1Fig. 7) in all modular Fytotextile types. Specifically, Fytotextile 3 and 4 presented the least number of dead plants followed by Fytotextile 1, and 2 in which more dead and unhealthy plants were observed (AppendicesPublication 1Table 4). Regarding variability among the plant species under examination, Erodium x variabile 'Roseum' presented the most satisfactory performance in all modules. On the contrary, the highest number of dead plants across all modules was recorded for Lavandula dentata. Simultaneously, the daily recorded substrate moisture levels (%) showed that Fytotextile 4 presented the lowest percentage followed by Fytotextile 1. Fytotextiles 3 and 2 presented variability through time that did not reveal a concrete moisture pattern while they exhibited the highest substrate moisture (AppendicesPublication 1Fig. 8). 3.2. Assessment of different LED lighting systems for indoor living walls This study consisted of two experiments testing the performance of Soleirolia soleirolii (Soleirolia) and Spathiphyllum wallisii (Spathiphyllum) under six different LED Doctoral thesis. Maria P. Kaltsidi 22 lighting systems (AF) (AppendicesPublication 2Table 1)., with D, E and F light sources being placed closer (system marked with ‘1’) or farther (system marked with ‘2’) from the feltbased living wall modules (AppendicesPublication 2Fig. 2). In terms of illuminance, the highest luminous flux per unit area was usually recorded at the middle of the upper module, while the lower illuminance was obtained at the bottom of each module (AppendicesPublication 2Fig. 3). In order of descending illuminance, the lighting systems were ranked as follows: E1, A, B, D1, F1, E2, F2, D2, C. Regarding the Photosynthetic Photon Flux Density (PPFD, μmol m−2 s-1), it was found to be higher at the middle of the upper modules (AppendicesPublication 2Table 2). The highest value was recorded for lighting system E1 and, decreasing, in: D1, F1, E2, A1, F2, D2, B1, C. Both illuminance and PPFD presented a sharp drop when the distance increased up to 1 m, followed by a milder decrease as the distance increased further (AppendicesPublication 2Fig. 4). All lighting systems presented a satisfactory correlation between illuminance and PPFD. A robust correlation was also identified between illuminance simulation and actual measured values (AppendicesPublication 2Fig. 5). Regarding temperature close to the modules, this was found to be ~5°C higher in modules A, B, C compares to D1, D2, E1, E2, F1 and F2. Among the latter, a small difference of ~1°C was recorded between almost all upper and lower modules. The relative humidity (5070%) was higher for D1, D2, E1, E2, F1 and F2 and among them, higher in D2, E2 and F2 (AppendicesPublication 2Fig. 7). Significant variability was observed among modules in terms of average daily water consumption, with the highest values being attributed to D2 and the lowest to B (AppendicesPublication 2Fig. 8). In reference to vegetation performance, the traits measured were: total, root and aerial fresh and dry weights (g plant−1), number of white flowers, green cover (%), Normalized Difference Vegetation Index (NDVI), and the relative measure of chlorophyll content (SPAD). Moreover, the indices on aerial to root dry weight and total fresh to total dry weight were calculated, while mean leaf area (cm2 leave-1) was measured only for Spathiphyllum plants. In general, the root and aerial fresh and dry weights presented Doctoral thesis. Maria P. Kaltsidi 23 their highest values in module A and their lowest in modules D2 and E2, in the case of Spathiphyllum (AppendicesPublication 2Table 3). For Soleirolia, the highest values were attributed to modules D1 and E1 and the lowest to modules C and F2 (AppendicesPublication 2Table 4). The upper modules exhibited a higher green cover compared to the lower modules, except for module C (AppendicesPublication 2Fig. 9) and the number of Spathiphyllum white flowers was high in modules D1, E1, F1, D2, E2 and F2, with no significant differences among them (AppendicesPublication 2Fig. 10). The mean NDVI after 4 and 10 weeks since planting was higher in module D2, while only module B did not present any significant differences between weeks 4 and 10 (AppendicesPublication 2Table 5). Furthermore, Spathiphyllum leaves were found to contain less chlorophyll in the upper modules of D1, E1 and F1, while the highest content was attributed to modules D2 and F2 (AppendicesPublication 2Fig. 11). Lastly, regarding both in the attractiveness of colours and in the natural appearance of plants under each lighting system (AppendicesPublication 2Fig. 12), observers preferred lamps D and F, followed by E. On the contrary, lamps A and C presented low values of acceptance by the questionees (AppendicesPublication 2Table 6). 4. General discussion of the results 4.1. Improving the performance of feltbased living wall systems in terms of irrigation management The aforementioned allegation of the need for continuous evaluation and development of the living wall systems is supported by the findings of the present study as the original Fytotextile® system (Fytotextile 1) exhibited inferior performance compared to its evolutions (Fytotextile 24). Precisely, Fytotextile 3 and 4 presented a higher water retention capacity and they conserved the water for a longer time due to the traits of the intermediate layers. However, the hydrophilic behavior of the interlayers of feltbased living wall systems must be taken into account to estimate whether there is high water availability for plant roots. In the current study, the Doctoral thesis. Maria P. Kaltsidi 24 vegetation was not affected by the hydrophilic performance of the intermediate layer, although further investigation with a longer duration is suggested to determine its influence over time. According to the findings of the drainage test, the elevated total volume of water drained for Fytotextile 4 was the result of the initial increase in water content prior to the irrigation events. This increased water content is due to the higher retention capacity of the Vivapol® intermediate layer. Thus, it is expected that irrigation frequencies lower than those currently tested (1, 2, 4, 8 events d-1) will present better results which allow further research focused on the use of the specific material. In contrast, Fytotextile 2 showed the lowest total volume of water drained potentially due to its fast drying capacity but elevated water storage. However, it exhibited the highest drainage flows in most cases and mainly at the beginning of the irrigation event, which makes the option of an irrigation program with shorter duration events inefficient. This result is consistent with the finding of PérezUrrestarazu et al. (2014) and Cortês et al. (2019) for modular systems. Regarding the application of the different irrigation schedules, it was concluded that the combination of high frequency and reduced duration is the optimal option, results that are in accordance with PérezUrrestarazu et al. (2014) study. Applying this irrigation schedule, the peak drainage flow would potentially be reduced in the initial stages of irrigation and the total volume of water drained would not be too elevated. Concerning the vegetation performance, there is no correlation between the plant losses or the low appearance results and the different Fytotextile systems. However, the application of longerterm studies is suggested to appreciate the influence of the living wall system on the distinct types of plants and the constant attention to the proper plant selection based on the needs of each plant type. The present study revealed new questions about the existence of various commercial feltbased living wall systems and their utilization on appropriate occasions. The selection of the living wall systems that will be considered appropriate in different environmental conditions should be based on prior long-term studies to test the Doctoral thesis. Maria P. Kaltsidi 25 performance of the materials used. From a sustainability point of view, the performance of materials should also focus on water and carbon footprint, as well as environmental benefits such as water and energy consumption, CO2 fixation, improvement of biodiversity, fertilization and the implementation of pesticides. 4.2. Assessment of different LED lighting systems for indoor living walls The use of indoor living walls frequently creates a need for auxiliary illumination that needs to be efficient in terms of enhancing vegetation and appearance, and, at the same time, have the least possible energy consumption and with low heat production. These aspects make LED lamps the obvious choice, yet, the lamps which produce more light within the PAR spectrum are considered ideal. Significant variance was observed among the different lighting systems under examination in terms of vegetation development and PPFD values. One of the findings that need to be highlighted is that the CFUT01 (C) lamp, though specifically designed for plant growth, was the one which exhibited the lowest PPFD values and the less adequate plant performance. This can be attributed to the fact that such lamps are designed to be placed at a very close distance from the plants, thus being unsuitable for being used to light living wall systems. Moreover, such lamps result in a nonnatural appearance of plants, which severely diminishes the ornamental value of the living wall. In addition, the vertical gradient of illuminance (Chen, 2005) is an additional factor that needs to be considered when evaluating lighting systems for indoor living walls. The results of the present study, slightly higher than the ones reported in the literature Thiel et al. (1996), indicated that the average loss of illuminance per metre of distance to the light source was between 48 % [Forum (F)] and 64% [Logar CMH Superflood (B)], with the exception of CFUT01 (C) lamp, for which the loss reached 78.6 %. It should be noted, though, that the loss was significantly higher in the first metre. Given the fact that PPFD values presented a similar, yet smoother, direct correlation to the distance from the lamp, it is suggested that the lower part of living walls cannot be Doctoral thesis. Maria P. Kaltsidi 26 at a large distance from the light source, as PPFD levels exhibit an acute decrease within the first few metres. Moreover, the vertical gradient introduces a lack of illuminance uniformity that needs to be considered when selecting plant species. Plants with higher light demands should be placed at the upper sections of the living wall, as the results of the present study indicated that uniformity values are considerably higher at the upper modules. In terms of PPFD values, the midsection of upper living walls was found to receive more light in all treatments, while PPFD values below the upper modules for Aster Ignia Green (A), Logar CMH Superflood (B), and CFUT01 (C) lighting systems were found to be inadequate for plant survival. According to this, different lamps should be used for living walls higher than 1 m. In order to assess the effect of the duration (number of hours) of artificial lighting on vegetation performance, the photosynthetic daily light integral (DLI) was estimated. DLI refers to the cumulative amount of PAR delivered to a specific area over a 24h period (Fausey et al., 2005). Regarding dry biomass production, the results of Soleirolia plants in the present study confirm that higher DLI values are correlated with higher dry biomass (Warner and Erwin, 2005; Oh et al., 2009). However, this argument could not be supported by the performance of Spathiphyllum plants, whose dry biomass did not increase at elevated DLI values, possibly due to Spathiphyllum’s high adaptation to lower light exposure. While Faust, (2001) proposed a DLI value of 4 mol m−2d-1 as ideal for Spathiphyllum plants, in the present study, Aster lamp (A) showed the highest dry biomass when receiving only 1.8 mol m−2d-1. Apart from any inconsistencies that need to be further investigated, it should be highlighted that Spathiphyllum was found to be more susceptible to DLI variations. Aster Ignia Green (A) and Logar CMH Superflood (B) lamps presented fewer flowers than Dahlia (D2) and Forum (F2) lamps. Given the fact that all those lamps were characterized by similar DLI values, the results are not in accordance with previous findings supporting that higher DLI induces higher flowering (Oh et al., 2009; Currey and Erwin, 2011). Though needed to be further examined, lack of variance among the Doctoral thesis. Maria P. Kaltsidi 27 aforementioned treatments might be associated with differences in temperature, a fact that it is known to affect flowering (Meng and Runkle, 2014; Blanchard et al., 2011). As expected, the lighting systems under examination were associated with different values of water consumption, with the highest one being attributed to Dahlia (D2) and the lowest to Logar CMH Superflood (B). While these results are in accordance with the literature Egea et al. (2014) in terms of variability, the values of daily water consumption recorded during the present study were much lower than the ones reported by the aforementioned authors. The modules that were closer to the light source presented a more robust vegetation cover, a trait of particular importance for living walls. Yet, it should be highlighted that Dahlia (D), Logar CLH Superflood (E), and Forum (F2) lamps, plants growing closer to the light source presented a deteriorating appearance in the course of time, a trend that was more acute for Soleirolia. Furthermore, plants in modules receiving a lower PPFD presented higher chlorophyll content, thus coinciding with literature (Dibenedetto, 1991; Krause and Winter, 1996; Zhang et al., 2016) suggesting an inverse correlation between luminous flux and chlorophyll content. Lower PPFD values were also associated with higher NDVI, a trend that has been previously reported (Mielke and Schaffer, 2010) and attributed to alternated pigment composition and protective mechanisms against excess light. Lastly, while Jost-Boissard et al. (2009) have reported that colour composition and temperature of lighting systems affect the opinion of the people observing the living wall; in the present study this could not be confirmed. The questionees were found to prefer lamps Dahlia (D) and Forum (F), which were the ones to luminous flux (lm) rather elevated than all other lighting systems though with no important colour and/ or temperature differences (AppendicesPublication 2Table 1), highlighting the importance of further examining the effect of the traits to the degree of acceptance by observers. Moreover, questionees show a higher level of acceptance towards lamps which produce a more homogenous light distribution rather than a single beam. Doctoral thesis. Maria P. Kaltsidi 28 5. General Conclusions 5.1. Improving the performance of feltbased living wall systems in terms of irrigation management The first study aimed at further assessment of the potential of the commercial feltbased living wall system, Fytotextile®, to improve the irrigation management by altering the materials used and applying the correct irrigation schedule in each case. Synopsizing the basic findings, it should be highlighted that: • Fytotextile 4 revealed the most increased capacity to store irrigation water compared to the other three Fytotextile systems. • Fytotextile 2 produced the smallest drainage volume in all irrigation schedules. • All Fytotextile types seemed to be adequate to house different vegetation types maintaining an elevated aesthetically result in the short term. Living walls with Fytotextile 3 and 4 presented the lowest plant losses, though with different substrate moisture levels (%), while Fytotextile 4 presented the lowest substrate moisture level and Fytotextiles 3 and 2 the highest. • Erodium x variabile 'Roseum' presented the most satisfactory performance in all Fytotextile systems while Lavandula dentata the worst. In conclusion, the results of the present study highlight, on the one hand, the potential of the materials used on felt-based living wall systems to contribute to the improvement of water management with a sustainable approach. On the other hand, it is revealed the importance of the implementation of the appropriate irrigation schedules and the lack of knowledge in this sector. It is suggested for living walls to be constructed with suitable and tested materials that can support long life living wall systems with the minimum losses in terms of water and materials (e.g. vegetation, geotextiles) in order to be effective in delivering the desired results. Doctoral thesis. Maria P. Kaltsidi 29 5.2. Assessment of different LED lighting systems for indoor living walls The second study aimed at the evaluation of six commercially available LED lighting systems regarding their suitability for indoor living walls. This evaluation was based on lighting pattern, temperature/ water consumption and effect on vegetation performance, along with the degree of acceptance according to questionees. According to the findings of this study: • Illuminance (as luminous flux per unit area) was found to be positively correlated to the height of the module for each pocket. PPFD was also higher at the middle upper module. Logar CLH Superflood lamp in treatment E1 presented the highest value for both traits, while the lowest values were attributed to CFUT01 lamp (treatment C). • Temperature was higher for lamps Aster Ignia Green, Logar CMH Superflood and CFUT01 (treatments A, B and C, respectively). Moreover, a small difference of ~1°C was recorded between almost all upper and lower modules of treatments in test 2 (D1, D2, E1, E2, F1 and F2). • Relative humidity (5070%) was higher for Dahlia (D2), Logar CLH Superflood (E2) and Forum (F2) lamps. • Dahlia (D2) exhibited the most elevated average daily water consumption and Logar CMH Superflood (B) the lowest. • Among the examined lighting systems, CFUT01 lamp (treatment C) was the only one that was not characterized as suitable for indoor living walls. Moreover, Aster (treatment A) and Logar CMH Superflood (treatment B) performed poorly when placed farther from the module. • Dahlia lamp (treatment D) was the one that received the highest level of approval among questionees. In conclusion, this study highlighted the impact of LED lighting systems on the performance of living walls, while revealing that, along with lamp type, other parameters such as its distance from the living wall, its orientation, beam angle, energy Doctoral thesis. Maria P. Kaltsidi 30 consumption and level of acceptance by the public should also be taken into consideration when evaluating the efficiency of lighting systems. References Ascione, F., R.F. De Masi, M. Mastellone, S. Ruggiero, and G.P. Vanoli. 2020. Green walls, a critical review: Knowledge gaps, design parameters, thermal performances and multi-criteria design approaches. Energies 13(9). doi: 10.3390/en13092296. Blanchard, M.G., E.S. Runkle, and J.M. Frantz. 2011. Energy-efficient greenhouse production of Petunia and Tagetes by manipulation of temperature and photosynthetic daily light integral. Acta Hortic. 893: 857–864. doi: 10.17660/ActaHortic.2011.893.94. Chen, C. 2005. Fluorescent lighting distribution for plant micropropagation. Biosyst. Eng. 90(3): 295–306. doi: 10.1016/j.biosystemseng.2004.10.005. Coma, J., G. Pérez, A. de Gracia, S. Burés, M. Urrestarazu, et al. 2017. Vertical greenery systems for energy savings in buildings: A comparative study between green walls and green facades. Build. Environ. 111: 228–237. doi: 10.1016/j.buildenv.2016.11.014. Cortês, A., J. Almeida, J. de Brito, and A. Tadeu. 2019. Water retention and drainage capability of expanded cork agglomerate boards intended for application in green vertical systems. Constr. Build. Mater. 224: 439–446. doi: 10.1016/j.conbuildmat.2019.07.030. Currey, C.J., and J.E. Erwin. 2011. Photosynthetic daily light integral impacts growth and flowering of several kalanchoe species. Horttechnology 21: 98–102. Curtius, L. 1932. The Geography of Stabo (L.C. Library, editor). XVI. Dibenedetto, A.H. 1991. Light environment effects on chlorophyll content in Aglaonema commutatum . J. Hortic. Sci. 66(3): 283–289. doi: 10.1080/00221589.1991.11516155. Doctoral thesis. Maria P. Kaltsidi 37 to optimise water retention and vegetation performance in harsh climate conditions. Therefore, three evolutions of the Fytotextile system were tested in terms of water retention capacity, drainage and vegetation performance. Fytotextiles 3 and 4 vastly improved the initial water retention capacity of the commercial system (2.9 and 5.8 times that of Fytotextile 1, respectively) but the former exhibited a lower volume of water drained and a slightly better behaviour of the plants. Keywords: Fytotextile; green walls; vertical greening systems; water management; water retention capacity 1. Introduction Nowadays, the use of vertical greening systems is spreading worldwide under different outdoor climates and microclimate conditions as well as indoor environments (Ghazalli et al., 2019; Medl et al., 2017; Pérez-Urrestarazu et al., 2015). However, despite the multiple known benefits and ecosystem services provided by them (Collins et al., 2017; Ghazalli et al., 2019; Larcher et al., 2018; Medl et al., 2017; Pérez et al., 2016), these green technologies are often subjected to criticism, especially regarding their maintenance and environmental sustainability. Precisely, the excessive water use becomes one of the main concerns (Manso and Castro-gomes, 2015; Riley, 2017). Regardless of the green wall technology used, watering the vegetation is compulsory, mostly by means of integrated irrigation systems (Medl et al., 2018). This is particularly important in the cases of installation in warm climates where a proper irrigation schedule can be critical for the performance or even the survival of the vegetation. However, water management related to living walls has not been broadly studied, so there is a knowledge gap in this matter (Pérez-Urrestarazu et al., 2015). There are different living wall systems in the market (Manso and Castro-gomes, 2015; Medl et al., 2017; Pérez-Urrestarazu et al., 2015). Some of them are based on boxes or containers, which limit the roots development (e.g., root-bound plants) as they are confined (Weinmaster, 2009) and, frequently, they do not allow enough gas exchange, leading to an undesirable reduction of their growth rate (Pallardy, 2008). As an alternative, the ‘felt’ (also referred to as ‘cloth’) systems are usually formed by at least Doctoral thesis. Maria P. Kaltsidi 38 two textile-like layers (a geotextile is the material most employed), in between which the plants are placed, bare rooted or in an inert substrate. The layers serve as a support to the plant and at the same time they act as a media to provide water and nutrients to the roots. This kind of systems solves the problem of excessive size (thickness) and weight of those based on containers. The major drawbacks of this system are its low water retention capacity which forces having frequent irrigation events to provide the water required by the vegetation (Pérez-Urrestarazu et al., 2014) and less water distribution uniformity (Pérez-Urrestarazu et al., 2014; Segovia-Cardozo et al., 2019). This is particularly problematic in warm climates and usually results in excessive water use (especially when the system is not recirculated). Also, as felt-based living walls can be considered a hydroponic system (since usually the plant’s organic medium of development is changed for an inorganic one) (Manso and Castro-gomes, 2015), additional nutrients must be incorporated (and part of them lost with the drainage water). In order to ameliorate these problems, some systems are composed of a special configuration of the geotextile layers, forming pockets where the plants are housed with their root ball, thus reducing the transplant stress. Hence, they can be considered as ‘semihydroponic’ systems. In this case, the outer layer must have a good air permeability to avoid problems of root asphyxia. The most commonly used irrigation system for living walls is localised irrigation using low flow emitters (drippers) placed in pipes at different heights of the living wall (PérezUrrestarazu and Urrestarazu, 2018). Due to the action of gravity and the capillarity of the inner geotextile layer based on cotton fibres, the water is distributed throughout the living wall surface (Pérez-Urrestarazu et al., 2014). This textile fabric should be able to absorb as much water as possible and retain it for a long time. This is difficult due to the reduced thickness of the felt (less volume for storage) and the vertical position in which it is placed. Hence, the challenge is to improve the properties of the system employed in order to maximise the water retention capacity and ease the management of the irrigation. The aim of this study is the assessment of the performance of four felt-based living wall systems in terms of water management (prioritising availability for the vegetation but minimising at the same time the water losses). To do so, four semi-hydroponic outdoor living walls were tested in order to evaluate (1) the water retention capacity and drying speed, (2) the volume of drained water and the maximum drainage flow obtained with different irrigation schedules (varying both their duration and the interval between irrigation events), and (3) the vegetation performance in each of them. Doctoral thesis. Maria P. Kaltsidi 39 2. Materials and methods 2.1.Experimental setup and systems tested The experiment was set in an exterior courtyard in the Aljarafe region of Seville, Spain (37º23'7 "N, 6º 6'53" W), which has a Hot-summer Mediterranean climate (Csa) according to the Köppen–Geiger climate classification system. It was conducted from November 2016 until July 2017. Four living walls of 2 by 1 m (height x width) were installed facing south using, in each one of them, two 1 x 1 m felt modules based on the Fytotextile® system (Terapia Urbana S.L., Seville, Spain), widely used in European countries (Figure 1). Each of them was comprised of different inner textile layers, having in common the outer layer composed of a sheet of polyamide and a waterproof back layer. The inner textile layer of each of the four types of Fytotextile modules tested was: - Fytotextile 1 (standard Fytotextile): 2.6 mm thick geotextile (Protex 300, Projar, Valencia, Spain) made of polypropylene and other recycled natural fibres (cotton, wool, etc.), which are non-woven and micro-perforated to improve their permeability to water, (unit weight: 300 g m-2). - Fytotextile 2: 4 mm thick geotextile (VLS-500, Diadem, APP Kft., Győr, Hungary), with the same composition of Fytotextile 1 (unit weight: 500 g m-2). - Fytotextile 3: another layer is added to the geotextile of Fytotextile 2. This layer is made of Aquaten (Aquaten Ltd., UK), a highly absorbent, engineered polymer fibre matrix blanket (1.2 mm thick) that enhances the water retention capacity. - Fytotextile 4: Fytotextile 2 geotextile plus and added layer made of Vivapol® (Reimann Emsdetten, Germany), a very highly absorbent (according to the manufacturer, with a water retention capacity of 3 L m-2), engineered polymer fibre blanket (4-5 mm). The outer and inner layers were attached by sewing with resistant synthetic yarn forming grids of 15 cm. Each living wall had 98 pockets (49 pockets/m2) in which the plants were inserted with their root balls. In order to protect the facade from damp problems, a third back layer was added to all the modules. To do so, a waterproof sheet of flexible PVC, sewn and thermo-sealed in the perimeter of the back of the modules, was used. Finally, in order to be able to fix the modules to the façade, a metallic fastening profile was screwed to an auxiliary metallic structure. Doctoral thesis. Maria P. Kaltsidi 40 Once the modules had been fixed to the structure, a horizontal pipe with drip emitters was placed in the upper part of each module between the mid and outer layer. Each irrigation line had 7 self-compensated emitters (Netafim, Israel) with a flow of 2 L h-1. The two irrigation lines were connected by a vertical pipe that led to the entrance of the water supply network (Figure 1). The irrigation control was performed with a programmer connected to four electrovalves, one for each system tested. The water inlet to the irrigation system was measured by a 3/4" MTK (ZENNER International GmbH & Co. KG, Germany) multi-stream cold water meter with pulse emitter (1 L pulse-1). To collect the water drained by each living wall a rectangular galvanized steel gutter was installed with a sufficient slope to pour the water into a Rain-O-Matic rain gauge (Ponamic, Denmark) with a reed relay connected to a digital pulse counter (Figure 1). In order to measure the substrate moisture content, 4 FDR model ECH2O EC-5 capacitive type soil moisture sensors (Decagon Devices, Pullman, WA, USA) were installed in the upper (H1) and lower(H2) row of each module (Figure 1). Figure 1. Schematic layout of the irrigation system and drainage collectors. 3D details of each Fytotextile system. Doctoral thesis. Maria P. Kaltsidi 41 A HOBO S/THB-M002 Temp/HR probe (Onset Corporation, Pocasset, Massachusetts, USA) with a resolution of 0.25° C and 1%, respectively, was used to monitor the air temperature and relative humidity. A HOBO S-LIB-M003 solar radiation probe (Onset Corporation, Pocasset, Massachusetts, USA) with a measurement range of 0 to 1280 W m-2 over a spectral range of 300 to 1100 nm was also employed. These sensors were placed at a distance of 0.3 m from the middle of the living walls. All the parameters were recorded in a HOBO model data logger H22-001-C (Onset Corporation, Pocasset, Massachusetts, USA). Three different experiments were performed in order to fulfil the three predefined objectives: water retention capacity and drying test, drainage test and plant performance test. 2.2. Water retention capacity and drying test This test was performed for all the modules without plants or substrate. The water holding capacity (WHC) gives information about how much water is retained/stored in the modules after water saturation. In order to obtain its value, three samples of each type of Fytotextile module were weighed using a Hyindoor portable digital electronic hanging scale with a maximum capacity of 50 kg when completely dry (after 48 hours of solar exposition) and then immersed in water for 30 minutes. Once saturated, they were removed from the water and placed vertically, eliminating by gravity all the water that was not retained. When the modules stopped dripping, they were weighed again. This procedure was repeated 3 times in order to obtain an average value for each module. The WHC was calculated as follows: 𝑊𝐻𝐶 (%) = 𝑊 𝑤− 𝑊𝑑 𝑊𝑑 Where Ww is the module wet weight and Wd, the dry weight. In order to determine the drying curve, they were vertically exposed to the sun under clear sky conditions, making ten weight measures during the day from 10:00 a.m. to 10:00 p.m. The experiment took place in September 2016. During this period, the temperature varied between 19 and 29°C, there was no rain, the relative humidity ranged between 23.1 and 60.5 %, and the maximum radiation was 785 W m-2. Doctoral thesis. Maria P. Kaltsidi 42 2.3. Drainage test The pockets of the living wall modules were filled with an equivalent volume to pots of 9 cm of diameter (0.2 L) of coconut peat (bulk density of 0.8 g cm3) but were not planted for this test in order to avoid the inclusion of other variables that could affect the results (different plant size and water uptake). This test was conducted between December 23rd, 2016 and January 15th, 2017. Seven different irrigation schedules (S1 to S7) were used (see Table 2 in the Results section) for the current study. In four of the irrigation schedules the irrigation time (5 minutes/irrigation) was the same, reducing the irrigation frequency (different daily dose of irrigation water). In the other 3 schedules, the daily irrigation doses were maintained but the number of irrigation events and their duration changed. Prior to the beginning of the drainage test, the flow rate discharged by the emitters was measured in order to determine the uniformity coefficient and mean values. Four replicates were performed for each irrigation schedule in consecutive days with similar initial substrate moisture and climatic conditions. In each repetition, the volume (L) of irrigation water applied and the drainage flow rates (L h-1) and total volume (L) recovered at the bottom of each living wall were registered for each living wall throughout the day. The substrate moisture in the central zone of each living wall, the incident solar radiation, the air temperature and the relative humidity were also measured to control the conditions in which the test was performed. 2.4.Vegetation performance test This experiment was conducted between May 27th and July 11th, 2017. In order to evaluate the plant performance in each of the living walls, three different species commonly found in outdoor living walls in warm climates were planted. The species selected, Carex oshimensis, Erodium x variabile 'Roseum' and Lavandula dentata, were placed in vertical rows (two, three and two rows, respectively) in order to avoid any influence regarding their height placement (Figure 2). The plants were acquired in a nursery with a pot size varying between 0.12 and 0.15 m of diameter, and a volume of 300 cm3 of substrate composed by a mixture of coconut fibre and peat. No additional nutrients were added with the irrigation water. Doctoral thesis. Maria P. Kaltsidi 43 Figure 2. Living wall systems (1 to 4), each one planted with Carex oshimensis 'Evergold' (right), Erodium x variabile 'Roseum' (middle) and Lavandula dentata (left). Two different irrigation schedules were used. There were three irrigation events per day in both of them, at 8:00 am, 2:00 pm and 7:00 pm, but with different durations: 15 minutes from May 27th to June 19th and 10 minutes from June 19th to July 11th. The objective of diminishing the irrigation duration was to evaluate the performance of the plants in a context of water shortage. The volume of irrigation and drainage water was registered for each living wall throughout the study period. The substrate moisture in the central zone of each living wall (Figure 1), the incident solar radiation and the air temperature and relative humidity were also measured to control the conditions in which the vegetation performance test was performed (Figure 3). Photographs of each of the four living walls were taken weekly in order to observe the evolution of the vegetation during the trial. Also, a visual inspection was performed, recording the number of dead plants and any anomalies detected concerning the normal expected plant development. Doctoral thesis. Maria P. Kaltsidi 44 Figure 3. Temperature (Temp, ºC) and Relative Humidity (RH, %) during the vegetation performance test 3. Results 3.1.Water retention capacity The results obtained in the characterisation of the WHC for the 4 types of water-saturated modules analysed are shown in Table 1. Fytotextile 4 is the one with the highest water volume stored (7.85 L m-2) followed by Fytotextile 3 (3.95 L m-2) and Fytotextile 2 (1.51 L m-2), with considerable higher values than the standard module (Fytotextile 1) (1.35 L m-2). Therefore, Fytotextile 4, 3 and 2 presented an increase in water retention of 481.5 %, 192.6 % and 11.9 %, respectively, compared to Fytotextile 1. Table 1. Average values for Fytotextile dry and wet weight (kg), maximum water stored per unit area (L m-2) and WHC (%) Fytotextile 1 Fytotextile 2 Fytotextile 3 Fytotextile 4 Wd (kg) 2.33 2.43 2.76 3.14 Ww(kg) 3.68 3.93 6.72 10.99 Water stored (L m-2) 1.35 1.51 3.95 7.85 WHC (%) 57.87 62.20 143.06 250.37 Figure 4 shows the drying rate for the different tested Fytotextile modules. It can be observed that Fytotextile 1 and 2 lost all the water retained 395 minutes (6 hours and 35 Doctoral thesis. Maria P. Kaltsidi 45 minutes) after the beginning of the drying phase. However, Fytotextile 3 and 4 kept much water after 10 hours, still showing water content values of 0.79 L m-2 and 4.16 L m-2, respectively. Figure 4. Evolution of the Fytotextile (1, 2, 3, 4) water content (L m-2) over 10 hours (drying curve) 3.2.Drainage test The mean total volumes and maximum flows of water drained in a day from the 4 types of Fytotextile living walls for the seven different irrigation schedules are summarised in Table 2. Important differences can be observed between the types of Fytotextile modules and the irrigation schedules used. Obviously, when the duration of the irrigation event was the same, , there was a higher volume of drained water in all the modules tested for higher irrigation frequencies, given that the modules still have some water retained from the previous irrigation event. Nevertheless, when the volume applied is the same in all the frequencies considered (S1, S5, S6 and S7), the differences in drainage volumes measured are lower (though the drainage volume is slightly higher when there are more irrigation events). Doctoral thesis. Maria P. Kaltsidi 46 Table 2. Average values of maximum drainage flow (Fmax, L h-1) and drained water volume (DWV, mm/d) for different irrigation schedules (S1 to S7) Fytotextile 1 produced the highest drainage volume in all the irrigation schedules tested, followed by Fytotextile 4 with an average reduction of drained water of 12.4 % over Fytotextile 1. Notwithstanding, according to the water retention capacity test, Fytotextile 4 is precisely the one that retains the highest volume of water. Hence, even for lower irrigation frequencies, its water content is still high. This fact leads to a higher volume drained, which means that for this system the irrigation duration or its frequency should be reduced even more. On the other hand, Fytotextile 2 generates the smallest amount of drainage water in all the cases (an average of 41.6 % smaller than Fytotextile 1), followed by Fytotextile 3 (37.1 % less drainage than Fytotextile 1) (Table 3). This difference is more remarkable for the lower irrigation frequencies. For instance, a reduction of 62 and 59.1 % was observed (for Fytotextiles 2 and 3, respectively) in the volume of drained water measured with one five-minute irrigation event per day. Fytotextile 2 showed, however, higher drainage peak flows than Fytotextile 1 for high frequencies (four or more irrigation events each day) while Fytotextile 3 produced the lowest values. Irrigation schedule Duration (minutes) Frequency (events d-1) Fytotextile 1 Fytotextile 2 Fytotextile 3 Fytotextile 4 Fmax (L h1) DWV (mm/ d) Fmax (L h-1) DWV (mm/ d) Fmax (L h1) DWV (mm/d ) Fmax (L h1) DWV (mm/d) S1 5 8 7.97 15.48 21.67 8.65 5.29 10.88 5.94 14.30 S2 5 4 3.05 7.29 8.85 4.36 2.21 4.79 2.46 6.68 S3 5 2 1.88 3.36 1.54 1.83 1.91 2.05 1.56 2.78 S4 5 1 1.56 1.37 0.64 0.52 1.76 0.56 0.78 0.90 S5 10 4 16.88 13.29 19.33 8.53 13.79 8.59 20.39 11.98 S6 20 2 36.41 11.74 23.33 8.06 21.32 7.96 28.13 11.22 S7 40 1 37.03 11.00 24.87 7.47 24.12 7.69 31.56 10.46 Doctoral thesis. Maria P. Kaltsidi 53 Apart from the results obtained, some other issues should be considered to determine which system is most suitable for the installation of a living wall. For instance, the standard module (Fytotextile 1) can be employed when the environmental conditions are not harsh (e.g., temperate climate, indoor locations), so an added water retention capacity is not really required. Also, the production costs, the manufacturing difficulties or the dynamic performance of the module are important variables to consider. For instance, Fytotextile 4 showed several deformations because of the expansion and contraction due to the hydration and drying phases, making it less suitable. In this sense, longer tests to assess the durability of the systems should be performed. The quantity and type of materials required should be considered too, as this influences both in the costs and the environmental impact. For example, only two layers are employed for Fytotextiles 1 and 2, while an additional polymer-based layer is added in Fytotextiles 3 and 4. As mentioned above, the different types of Fytotextile studied are made using various materials. Some of them, such as polypropylene, have the possibility of being recycled later, when the lifespan of the living wall is over. However, in the future, it could be interesting to carry out other assessments such as a life cycle analysis, or calculating the carbon or water footprint. With that information it would be possible to make a more indepth comparison between the different systems, also taking into account other parameters such as water consumption, energy consumption, CO2 fixation, biodiversity enhancement, and other environmental benefits. In this way, it would be possible to choose those systems that are most suitable from the point of view of sustainability. 5. Conclusions When using a felt-based system, its characteristics in terms of material selection and performance, number of layers, production cost and ease of manufacturing has proven to be important. There is a great abundance of various materials potentially appropriate for living wall systems. Thus, in the current study, three different evolutions of a broadly used standard commercial Fytotextile® system were assessed. The correct selection and combination of the materials affected several variables such as the water retention capacity and its duration, the drying speed of the system as well as the plant performance thus the sustainability of the living wall system. Doctoral thesis. Maria P. Kaltsidi 54 However, not only the importance of a suitable irrigation management should be taken into account when selecting materials. The sustainability of the living wall system is provided by a complexity of parameters that need to be studied in the whole. For instance, further studies about the environmental impact of the materials used are necessary. The irrigation performance is subjected, among other variables, to the system employed to build a proper, complete, and successful living wall. An adequate management of irrigation is required to keep a living wall in good condition, since a lack of water supply in periods of maximum demand can quickly produce a dehydration of the growing media and cause irreversible damages to the plants´ health. The choice of a suitable irrigation schedule (number of irrigation events and their duration) had a great impact on the results. Short irrigation events and higher frequencies are expected to help to enhance the water use efficiency. This would lead to less water usage and, consequently, more sustainable living wall systems. In any case, the water content of the living wall must be enough to ensure a correct appearance of the vegetation, as it is an important factor which can profoundly affect the aesthetic value and maintenance costs, as well as the sustainability, of a green wall installation. Given the complexity of the water management of living walls, further and long-term scientific analysis is necessary in order to obtain affordable and sustainable green wall systems. An improvement and optimisation of the existing commercial systems coupled with expanding knowledge to help irrigation scheduling could lead to reaching this goal. The proper material selection and improvement of the irrigation management will also facilitate the plant selection process. Species less resistant to water scarcity could be incorporated, expanding the range of plants that could be used on green walls under demanding climate conditions. Thus, new market options in locations with extreme climate conditions (hot and dry, with not much water available) could be opened. Acknowledgments We would like to thank the company Terapia Urbana S.L. for providing the materials to build the living walls for the tests. Doctoral thesis. Maria P. Kaltsidi 55 References Collins, R., Schaafsma, M., Hudson, M.D., 2017. The value of green walls to urban biodiversity. Land use policy 64, 114–123. Cortês, A., Almeida, J., de Brito, J., Tadeu, A., 2019. Water retention and drainage capability of expanded cork agglomerate boards intended for application in green vertical systems. Constr. Build. Mater. 224, 439–446. doi:10.1016/j.conbuildmat.2019.07.030 Ghazalli, A.J., Brack, C., Bai, X., Said, I., 2019. Physical and Non-Physical Benefits of Vertical Greenery Systems: A Review. J. Urban Technol. 1–26. doi:10.1080/10630732.2019.1637694 Larcher, F., Battisti, L., Bianco, L., Giordano, R., Montacchini, E., Serra, V., Tedesco, S., 2018. Sustainability of Living Wall Systems Through An Ecosystem Services Lens, in: Urban Horticulture. pp. 31–51. doi:10.1007/978-3-319-67017-1_2 Manso, M., Castro-gomes, J., 2015. Green wall systems: A review of their characteristics. Renew. Sustain. Energy Rev. 41, 863–871. doi:10.1016/j.rser.2014.07.203 Medl, A., Florineth, F., Kikuta, S.B., Mayr, S., 2018. Irrigation of ‘Green walls’ is necessary to avoid drought stress of grass vegetation (Phleum pratense L.). Ecol. Eng. 113, 21–26. doi:10.1016/J.ECOLENG.2018.01.007 Medl, A., Stangl, R., Florineth, F., 2017. Vertical greening systems – A review on recent technologies and research advancement. Build. Environ. 125, 227–239. doi:10.1016/j.buildenv.2017.08.054 Pallardy, S.G., 2008. Enzymes, Energetics, and Respiration, in: Physiology of Woody Plants. Elsevier, pp. 169–197. doi:10.1016/B978-012088765-1.50007-5 Pérez-Urrestarazu, L., Egea, G., Franco-Salas, A., Fernández-Cañero, R., 2014. Irrigation Systems Evaluation for Living Walls. J. Irrig. Drain. Eng. 140, 04013024. doi:10.1061/(ASCE)IR.1943-4774.0000702 Pérez-Urrestarazu, L., Fernández-Cañero, R., Franco-Salas, A., Egea, G., 2015. Vertical Greening Systems and Sustainable Cities. J. Urban Technol. 22, 65–85. Doctoral thesis. Maria P. Kaltsidi 56 doi:10.1080/10630732.2015.1073900 Pérez-Urrestarazu, L., Urrestarazu, M., 2018. Vertical Greening Systems: Irrigation and Maintenance, in: Pérez, G., Perini, K. (Eds.), Nature Based Strategies for Urban and Building Sustainability. Butterworth-Heinemann, Elsevier, pp. 55–63. doi:https://doi.org/10.1016/B978-0-12-812150-4.00005-7 Pérez, G., Coma, J., Barreneche, C., De Gracia, A., Urrestarazu, M., Burés, S., Cabeza, L.F., 2016. Acoustic insulation capacity of Vertical Greenery Systems for buildings. Appl. Acoust. 110, 218–226. doi:10.1016/j.apacoust.2016.03.040 Riley, B., 2017. The state of the art of living walls: Lessons learned. Build. Environ. 114, 219–232. doi:10.1016/j.buildenv.2016.12.016 Segovia-Cardozo, D.A., Rodríguez-Sinobas, L., Zubelzu, S., 2019. Living green walls: Estimation of water requirements and assessment of irrigation management. Urban For. Urban Green. 46, 126458. doi:10.1016/j.ufug.2019.126458 Weinmaster, M., 2009. Are green walls as “green” as they look? an introduction to the various technologies and ecological benefits of green walls. J. Green Build. 4, 1– 18. doi:http://dx.doi.org/10.3992/jgb.4.4.3 Doctoral thesis. Maria P. Kaltsidi 57 2. Publication 2 Assessment of different LED lighting systems for indoor living walls Maria P. Kaltsidia, Rafael Fernández-Cañerob, Luis Pérez-Urrestarazua,* a Urban greening and Biosystems Engineering research group. Area of Agro-Forestry Engineering. Universidad de Sevilla. ETSIA Ctra. Utrera km.1, 41013. Seville. Spain. Email addresses: [email protected], lper[email protected] b Urban greening and Biosystems Engineering research group. Department of AgroForestry Sciences. Universidad de Sevilla. ETSIA Ctra. Utrera km.1, 41013. Seville. Spain. E-mail address: [email protected] *Corresponding author: Telephone number: +34 954486480; E-mail address: [email protected] Abstract Building-integrated vegetation systems, such as living walls (LW), are becoming common tools for improving the sustainability of cities as well as an aesthetic resource. When used indoors, LW usually require a lighting system to ensure both an adequate plant development and a correct appearance. In this study, six commercial LED lighting systems are tested in order to assess their suitability for the proper performance of LW. The LW monitored were composed of two plant species (Soleirolia soleirolii and Spathiphyllum wallisii) frequently used in indoor LW. All the lamps tested (Aster and Dahlia of Ignia Green, Logar CMH, CLH and Forum of Lledó) proved to be apt for their use to light LW (except for the case of CF-UT01 of Panda Grow), as they showed a favourable performance in terms of plant development, with few differences between them in biomass production and green cover. The tested Aster (Ignia Green) and Logar CMH (Lledó) lamp models were not efficient for long distances between the vegetation and the light source. Despite these results, as illumination is one of the factors that determines the indoor ambience, aesthetics and viewers’ preferences were also studied. According to the observers' perception, the Dahlia model (Ignia Green) was preferred by 54.4 % of the respondents, while the rest of the lamps were preferred less. Doctoral thesis. Maria P. Kaltsidi 58 Keywords: vertical greening system, ornamental lighting, plant development, urban greening, viewer’s perception Nomenclature Symbol Units ADW: Aerial Dry Weight g plant-1 AFW: Aerial Fresh Weight g plant-1 CRI: Colour Rendering Index -- ET: Evapotranspiration l d-1 LED: Light-Emitting Diodes -- LW: Living Wall (s) -- PAR: Photosynthetically Active Radiation -- PPFD: Photosynthetic Photon Flux Density mol m-2 s-1 RDW: Root Dry Weight g plant-1 RFW: Root Fresh Weight g plant-1 RH: Relative Humidity % Soleirolia: Soleirolia soleirolii -- Spathiphyllum: Spathiphyllum wallisii -- SPAD: relative measure of chlorophyll content -- T: Temperature ºC TDW: Total Dry Weight g plant-1 TFW: Total (whole-plant) Fresh Weight g plant-1 LA: mean Leaf Area cm2leave-1 Introduction Nowadays, the inclusion of vegetation in the built environment in the form of green roofs and vertical greening systems is spreading. They are usually located outdoors, but in the case of living walls (LW), indoor installations are becoming frequent, given the multiple benefits which they offer, improving indoor air quality (particles and VOC retention), environmental conditions (temperature and humidity levels), acoustics and wellbeing (Gunawardena and Steemers, 2019; Moya et al., 2019). However, when plants are grown inside a building, one of the main constraints is the light that they receive. The available natural light in indoor environments is frequently not sufficient, thus auxiliary artificial lighting is often required for adequate plant growth and development (Tan et al., 2017). Doctoral thesis. Maria P. Kaltsidi 59 Selecting the proper lighting system for indoor plant growth is a demanding process that requires an accurate prior study. It should ensure certain characteristics in terms of intensity (the amount of light received by the vegetation) and quality (the spectral composition of the light source) (GOTO, 2003). In the case of LW, regulating the intensity is even more complicated, given that the lamps are usually located in the ceiling, so the lighting is not uniform over the entire vertical surface. In terms of quality, not only obtaining an effective spectral range is essential but also ensuring that the LW have a proper appearance (Egea et al., 2014). Artificial lighting technologies have been used in crop production for many years, with incandescent, fluorescent or high-intensity discharge lamps having been those most employed. However, the advance of solid-state lighting using light-emitting diodes (LEDs), with a great technical development in the last years and an important cost reduction, has displaced the other types of lamps. LEDs show several advantages such as a much longer lifespan and producing a high luminous flux with a low radiant heat output (Morrow, 2008; Yeh and Chung, 2009). This makes them more competitive in energy efficiency and economic terms (Singh et al., 2015). LEDs also have the ability to emit in a controlled spectral composition (Olle and Viršile, 2013), which is an advantage when growing plants. Given that LEDs emit in a very narrow spectrum (20-40 nm), the specific peak absorption bands of chlorophyll can be targeted. This improves the use of energy as most emitted light can be used for photosynthesis. Precisely, that is the basis of commercial LED grow lights, which mainly emit in the blue and red regions. Nevertheless, they give plants an unnatural appearance due to their colour (red/blue), so they are not so apt for aesthetical purposes, including LW lighting. In addition, some studies indicate that a better plant growth is achieved when using a broader spectrum with additional wavelengths (Kim et al., 2006). This makes white light more adequate. In order to obtain white LEDs, blue LEDs are usually coated with phosphor. Though this makes them less efficient than the single-wave-peak LEDs, the visualisation of plants greatly improves (Massa et al., 2008). In artificial lighting, the term white light refers to light formed by a mixture of colours. However, not all whites are the same, since they depend on the colours that compose them. In this sense, a white with a higher proportion of red will favour a "warmer" lighting and a white with a higher proportion of blues will give a "cooler" appearance. Colour temperature is used to classify the different types of white light and to facilitate Doctoral thesis. Maria P. Kaltsidi 60 comparison with "full spectrum" sunlight (Morrow, 2008). This concept refers to the type of light that a black body radiates when heated to a specific temperature, so that the higher the colour temperature, the colder the light source. For instance, at 2,000-3,000 K, the colour of the light will look white yellow; at 4,000 K, neutral white, and at 5,000-7,000 K, cold white. Shaw (2018) suggested that colour temperature has an effect on the growth of hydroponic lettuce seedlings, as plants under 6,000 K lights grew more than under 3,000 K. However, even when two light sources have the same colour temperature, the surfaces can be seen in different colours, given that two lights that appear to produce the same white may be the result of different wavelength mixes. For this reason, the concept of colour rendering is used to elucidate the similarity between the natural colour of an object (that is, in daylight conditions) and its colour under artificial lighting. Based on this concept, the colour rendering index (CRI) classifies light sources according to their colour rendering properties: the higher the CRI, the closer it is to natural colour. LED lighting in horticultural production has been widely addressed (Islam et al., 2012; Massa et al., 2008; Morrow, 2008; Olle and Viršile, 2013; Samuoliene et al., 2013; Singh et al., 2015), but it has not been studied when it is used with an ornamental purpose (as is the case of LW illumination). Only Tan et al. (2017) and Egea et al., (2014) have addressed this topic. The former quantified the impact of growth light provision on indoor greenery and the light compensation point of two ornamental species. The latter analysed different artificial lighting systems for LW, but in their study LEDs were not contemplated. The main objective of the current study was to assess the adaptation of six different commercial LED lamps (five of which were not specifically designed for plant growth) for the lighting of indoor LW. Both the performance and correct development of the vegetation under each lamp and its appearance were taken into consideration. The study was completed with an analysis of public preferences. Materials and methods Experimental setup and tests performed The study was performed at the Urban Greening Laboratory of the School of Agricultural Engineering of the University of Seville (Seville, Spain), with no natural light. Six different types of lamps were tested in this study and two experiments were carried out. Five of the lamps were conventional white LED lamps (4000 K) while one (C) was a Doctoral thesis. Maria P. Kaltsidi 61 commercial Grow-LED lamp specially designed for plant cultivation. Table 1 presents the main characteristics of each lamp and Figure 1 shows the relative emission intensity spectrum, when available. The first experiment involved lamps A to C and was conducted over the period mid-May to end-July 2018 (68 days). During this period, the daily mean room temperature and relative humidity were 24.9±0.7ºC and 68± 5 %, respectively. Lamps D, E and F were tested in a second experiment from mid-February to end-April (70 days). In this case, the daily room temperature was 22.4 ± 0.6 ºC and the relative humidity was 56 ± 7 %. Figure 1. Relative emission intensity (%) spectrum for a) Lledo, Forum lamp b) Lledo, CMH, CLH lamps and c) Ignia Green, Aster and Dahlia. (Graphs courtesy Lledo and Ignia green, images modified) Doctoral thesis. Maria P. Kaltsidi 62 Table 1. LED lamps used in the study and their characteristics. The different letters (A, B, C, D, E, F) refer to different lamp type treatments and the different numbers (1 or 2) refer to module closer (1) or farther (2) to the light source. Lamp Model Projector Curves Dimensions Manufacturer LW module Power (W) Flux (lm) CRI Beam angle (º) Colour temperature (K) Type of light Aster Ignia Green (Girona, Spain) A1 40 2.575 >90? 36º 3.700 White Logar CMH Superflood Lledó (Madrid, Spain) B1 35 2.650 >90 31º 4.000 White CF-UT01 NA Panda Grow (Shenzhen, China) C1 100 5.000 NA 120º NA Blue/red Dahlia Ignia Green (Girona, Spain) D1-D2 110 7.950 >90? 97º 3.700 White Logar CLH Superflood Lledó (Madrid, Spain) E1-E2 48 3.300 >90 *41º 4.000 White Forum Lledó (Madrid, Spain) F1-F2 83 7.350 >80 68º 4.000 White * Due to its small beam angle, two identical lamps of this model were placed at the same spot with different angles pointing at the centre of each of the two modules. NA: Not available Doctoral thesis. Maria P. Kaltsidi 69 for D2, E2 and F2, respectively). Module C received very poor values (7 mol m-2 s-1 in average). Table 2. Mean Photosynthetic Photon Flux Density values (mol m-2 s-1) for all lamps (A to F) in the upper (1) and lower (2) modules at three different heights (Up, Mid, Down) within each module. A B C D E F 1 Up 28.9 13.3 7.3 62.6 58.6 58.0 Mid 55.2 43.7 7.7 78.7 109.9 88.8 Down 23.0 19.8 5.9 74.2 78.9 34.0 2 Up 1.9 2.9 2.2 38.3 73.8 44.1 Mid 0.6 0.7 1.2 26.0 52.7 32.3 Down 0.4 0.3 0.8 19.2 19.9 20.4 Both the illuminance received and the PPFD depend, among other factors, on the distance to the light source. Figure 4 shows the different values of these two factors according to the distance from the LW to the different lamps tested. In the first metre, the values severely decrease, while this decrease is observed to be less intense as the distance increases. Figure 4. Illuminance (left) and Photosynthetic Photon Flux Density (right) at different distances from the light source for each lamp. Doctoral thesis. Maria P. Kaltsidi 70 Figure 5 represents the relation between the measured values of illuminance vs the PPFD for the different lamps, hence obtaining the conversion equations between both factors, which are distinct for each lamp. Lamp A exhibited a good relation, comparing to the rest lamps, where then minimum illuminance of 420 lx corresponds to 5.8 mol m-2 s-1 and a 1048 lx corresponds to 13.2 mol m-2 s-1. Lamp C presented the most elevated PPFD value (22.2 mol m-2 s-1) in 1136 lx, though, to be achieved, a short distance of 0.5 m is required (Figure 4). Lamp D had the highest PPFD value (94.8 mol m-2 s-1) when illuminance reaches 7204 lx. Lamp E showed a good relation between PPFD and illuminance. Figure 5. Relation between illuminance (lx) and Photosynthetic Photon Flux Density. Finally, an illuminance simulation of both tests was performed in DIALux evo (Figure 6), showing a very similar pattern of lux levels to that depicted in Figure 3. The Pearson correlation coefficients results (0.95, 0.98, 0.92, 0.89, 0.95, 0.88, 0.79, 0.77 and 0.98 for modules A, B, C, D1, D2, E1, E2, F1 and F2, respectively) exhibited that the correlation between the simulations (Figure 6) and the actual measured values (Figure 3) was high, being slightly inferior for the lower modules.). Doctoral thesis. Maria P. Kaltsidi 71 Figure 6. Simulation of illuminance levels for Test 1 (up) and Test 2 (down) using DIALux evo software and Pearson correlation coefficients (r) between the simulation and the measured illuminance values (lx). Temperature and water consumption The evolution of the temperature (T) close to each module is depicted, for both tests, in Figure 7. Variations in T were within 5ºC even between tests. The average T of test 1 and test 2 differed by 3ºC. During test 2, a difference of 1ºC on average was observed between Doctoral thesis. Maria P. Kaltsidi 72 the upper and lower modules except for D1 and D2 which did not differ. RH ranged between 50 % and 70 %. The average values were higher for the first test. In the second test, the RH was lower in the upper modules compared to the lower ones. Figure 7. Evolution of the mean daily temperature near each living wall module during both tests The average daily water consumption ranged between 1 and 1.5 L m-2 d-1 (Figure 8), resulting in more water consumed in module D2 (50.4 L) compared to B (35.2 L). Statistically significant differences (F = 2.834198; P-value = 0.00617977) in the average daily water consumption values were observed. Doctoral thesis. Maria P. Kaltsidi 73 Figure 8. Water consumption in the different living wall modules: (a) Cumulative evolution during the tests (L) and (b) mean daily values (L m-2 d-1). Different letters at the bottom of the bars indicate significant differences following Duncan’s multiple range test (P< 0.05) Vegetation performance Plant biomass produced in each of the LW modules was calculated at the end of the tests. Both fresh and dry weights per plant were measured for the aerial and root parts. Total leaf area (TLA) was also obtained only for Spathiphyllum. In the case of Spathiphyllum (Table 3), differences in fresh weight were more significant in the aerial part,while significant differences were exhibited only in the root system of module A. Module A had the higher fresh weights, while E2 presented the lowest. No differences were observed in fresh weight within modules lighted by lamps D, E and F. However, looking into their dry weights, the only significant difference occurred in the aerial part between E1 and D2. Even though no significant differences between upper and lower modules were observed, dry biomass in lower modules was 82.2 % of the average observed in the upper ones. Plants in module D2 had the lowest dry biomass, being 57 % of the obtained in module A, which produced the highest value (significantly different to the rest, excepting modules B and E1). There were no significant differences in leaf area. Table 4 shows the biomass production for Soleirolia plants. In this case, a much lower weight per plant was obtained in module C (especially regarding the aerial part), followed by F2.The total dry weight of plants in module C was 35 % of that obtained in D1 and E1. Plants grown in lower modules had, on average, 66 % of the dry weight of the plants in the upper modules. However, lamps D and F showed significant differences between the upper and lower modules only due to the root part, and no differences were found for lamp E. Precisely, lamp F was the one with a lower biomass production in the lower modules, as the average total dry weigh of plants in module F2 was 57 % of that observed in E2 (though no statistically significant differences were found between both). Doctoral thesis. Maria P. Kaltsidi 74 Table 3. Weights and leaf area of Spathiphyllum plants. TFW: total fresh weight; RFW: root fresh weight; AFW: aerial fresh weight; TDW: total dry weight; RDW: root dry weight; ADW: aerial dry weight; LA: mean leaf area. Measured variables LW module P-value A B C D1 E1 F1 D2 E2 F2 TFW (g plant-1) 170.5a 134.9b 112.8bc 94.4cd 102.0cd 97.8cd 88.7cd 82.5d 93.5cd 0.0000 RFW (g plant-1) 43.50a 30.04b 21.30b 22.53b 26.82b 26.94b 23.18b 26.08b 24.43b 0.0005 AFW (g plant-1) 126.9a 104.82b 91.47bc 71.84d 75.22cd 70.91d 65.53d 56.41d 69.05d 0.0000 TDW (g plant-1) 14.89a 12.29ab 10.71bc 11.29bc 12.53ab 10.94bc 8.50c 9.95bc 10.12bc 0.0150 RDW (g plant-1) 3.94a 2.65abc 1.41c 2.60abc 3.55ab 2.92abc 2.05abc 3.06abc 2.39abc 0.0478 ADW (g plant-1) 10.94a 9.64ab 9.31ab 8.70bc 8.98abc 8.02bcd 6.44d 6.89cd 7.73abc 0.0014 ADW / RDW 2.78 3.64 6.60 3.35 2.53 2.75 3.14 2.25 3.23 - TFW / TDW 11.5 11.0 10.5 8.4 8.1 8.9 10.4 8.3 9.2 - LA (cm2leave-1) 15.73bc 14.27c 14.70bc 15.07bc 14.10c 13.28c 17.53b 14.20c 13.13c 0.0768 For each row, mean values followed by different letters indicate significant differences following Duncan’s multiple range test (P< 0.05) and each value is the mean of six replicates (n=6) per experimental unit (A, B, C, D1, E1, F1, D2, E2, and F2). Doctoral thesis. Maria P. Kaltsidi 75 Table 4. Weights determined for Soleirolia plants. TFW: total fresh weight; RFW: root fresh weight; AFW: aerial fresh weight; TDW: total dry weight; RDW: root dry weight; ADW: aerial dry weight. Measured variables LW module P-value A B C D1 E1 F1 D2 E2 F2 TFW (g plant-1) 65.3bcd 61.0cde 36.1e 92.2ab 104.1a 70.2bcd 77.4abcd 84.4abc 51.4de 0.0001 RFW (g plant-1) 10.5e 10.3e 11.6de 29.4ab 32.7a 24.4bc 19.1cd 21.2bc 8.1e 0.0000 AFW (g plant-1) 54.8ab 50.6ab 24.5c 62.8ab 71.4a 45.8bc 58.2ab 63.2ab 43.4bc 0.004 TDW (g plant-1) 9.73ab 8.83ab 3.93d 11.14a 11.20a 7.75abc 7.00bcd 8.12ab 4.67cd 0.0000 RDW (g plant-1) 1.52cd 1.28cd 1.32cd 3.92a 3.73ab 2.59bc 1.74cd 1.74cd 0.74d 0.0000 ADW (g plant-1) 8.21a 7.56ab 2.62d 7.22ab 7.47ab 5.16bcd 5.26ab 6.38abc 3.92cd 0.0002 ADW / RDW 5.40 5.91 1.98 1.84 2.00 1.99 3.02 3.67 5.30 - TFW / TDW 6.7 6.9 9.2 8.3 9.3 9.1 11.1 10.4 11.0 - For each row, mean values followed by different letters indicate significant differences following Duncan’s multiple range test (P< 0.05) and each value is the mean of seven replicates(n=7) per experimental unit (A, B, C, D1, E1, F1, D2, E2, and F2).. Doctoral thesis. Maria P. Kaltsidi 76 The evolution of the green cover expressed by the % of the LW module covered by vegetation is shown in Figure 9. The vegetation initially covered around 28 % of the LW modules and differences were already appreciated from the first week after planting. In general, the upper modules showed a higher green cover, exceeding 80 % of the LW module covered by vegetation at the end of the test in A, B and D1. E1 and F1 reached 79 % and 73 %, respectively. Module C, however, presented a much lower coverage (64 %), similar to that obtained in the lower modules of the second test (67 %, 65 % and 71 % for D2, E2 and F2, respectively). Figure 9. Evolution of the green cover (GC, %) in the different living wall modules The number of Spathiphyllum white flowers in each LW module is shown in Figure 10 on a weekly basis. There was a big difference between tests, but not as much between the lamps used. In the first one, the average number of flowers was 11, 18 and 12 for modules A, B and C, respectively. In contrast, an average of 43, 50, 45, 46, 44 and 43 flowers were observed in D1, E1, F1, D2, E2 and F2, respectively. Doctoral thesis. Maria P. Kaltsidi 77 Figure 10. Evolution of the number of Spathiphyllum white flowers in the different modules Table 5 shows the mean NDVI values obtained at the middle and end of each test. All the values ranged between 0.68 (C and E1) and 0.91 (D2). After four weeks since planting, all the values were fairly similar, though C already showed the lowest NDVI value. Modules A, B, C and F2 maintained or a slightly increased NDVI at the end of the tests. However, the NDVI decreased in D1, E1 and F1, showing lower values than the rest of the modules (even C). Conversely, the NDVI was considerably higher for D2 and E2 at the end of the test. Only module B did not show significant differences between weeks 4 and 10. Table 5. Mean Normalized Difference Vegetation Index (NDVI) values taken for each living wall module four and ten weeks after planting Module Week A B C D1 E1 F1 D2 E2 F2 4 0.75de* 0.79c 0.68f* 0.82ab* 0.77cd* 0.79bc* 0.83a* 0.74e* 0.79c* 10 0.77d 0.79c 0.71e 0.69ef 0.68f 0.70e 0.91a 0.84b 0.82b Doctoral thesis. Maria P. Kaltsidi 78 Different letters in a row show statistically significant differences among the treatments of each week (week 4th and week 10th) and the asterisk (*) indicates the statistically significant differences between the treatments in both weeks (e.g. module A week 4 compared to module A week 10). The chlorophyll content in Spathiphyllum leaves in each module was measured at the end of the tests and the average SPAD values are presented in Figure 11. The lowest values were observed in the upper modules in the second test (D1, E1 and F1), ranging between 41.4 and 44.1. D2 and F2 had the highest values 54.9 and 54.1, respectively). Figure 11. Average SPAD values measured in Spathiphyllum at the end of each test. Different letters indicate significant differences according to Duncan’s Multiple Range test (P< 0.05) and each value is the mean of three replicates per experimental unit (A, B, C, D1, E1, F1, D2, E2, and F2). Observers’ perception In order to assess the visual quality, the observers were asked if the lights (Figure 12) produced attractive colours and a natural appearance of the plants (Table 5). Lamps D and F were the ones with the highest scores in both questions, followed by E. Lamps A and C got the lowest values. In fact, when the participants were asked to rank the lamps in order of preference, lamp D was chosen in the first position by 54.4 % of the Doctoral thesis. Maria P. Kaltsidi 85 Conclusions When artificial lighting is required for indoor greenery, selecting the most efficient lamps is very important, as the wrong choice may be crucial for the survival of a green wall. All the commercial LED lamps tested in this study, except for lamp C which was precisely the one designed for crop production, are apt for LW lighting. However, their placement (the distance from the LW, the beam angle, the lamp orientation) should be based on the lamp characteristics and plays an important role in obtaining a proper result. Energy consumption should also be considered, as some lamps use the energy more efficiently to produce light in the spectrum which is more usable by the plants. Lastly, the visual quality of the light in terms of producing a natural appearance of the vegetation is important in order to be pleasant for observers. Acknowledgments We would like to thank the spin-off company Terapia Urbana for providing the materials to build the living wall prototypes. We are also grateful to the companies Lledó and Ignia Green who lent us the lamps for the tests. 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