Seasonal and inter-annual variation in the chlorophyll content of three co-existing Sphagnum species exceeds the effect of solar UV reduction in a subarctic peatland

Hyy yläinen e al. Sp inge Plus (2015) 4:478 DOI 10.1186/s40064-015-1253-7 RESEARCH Seasonal andin e -annual a ia ion in he chlo ophyll con en o  h ee co-exis ing Sphagnum species exceeds he e ec o sola UV educ ion ina suba c ic pea land Anna Hyy yläinen1*, Pasi Rau io2, Minna Tu unen3 and Sa u Hu unen1 Abs ac We measu ed chlo ophyll (chl) concen a ion and chl a/b a io in Sphagnum bal icum, S. jensenii, and S. lindbe gii, sam- pled a e 7 and 8 yea s o ul a iole -B (UVB) and empe a u e manipula ion in an open ield expe imen in Finnish Lapland (68°N). We used plas ic il e s wi h di e en ansmi ance o UVB adia ion o manipula e he en i onmen al condi ions. The plan s we e exposed o (1) a enua ed UVB and inc eased empe a u e, (2) ambien UVB and inc eased empe a u e and (3) ambien condi ions. Chlo ophyll was ex ac ed om he capi ula o he mosses and he con en and a/b a io we e measu ed spec opho ome ically. Seasonal a ia ion o chlo ophyll concen a ion in he mosses was species speci ic. Tempe a u e inc ease o 0.5–1 °C and/o a enua ion o sola UVB adia ion o ca. one i h o he ambien (on a e age 12 s. 59 uW/cm2) had li le e ec on he chlo ophyll concen a ion o i s seasonal a ia ion. In he dominan S. lindbe gii, UVB a enua ion unde inc eased empe a u e led o a ansien dec ease in chlo ophyll concen a ion. Al oge he , species-speci ic pa e ns o seasonal chlo ophyll a ia ion in he s udied Sphagna we e mo e p onounced han empe a u e and UVB ea men e ec s. Keywo ds: Sphagnum bal icum, Sphagnum jensenii, Sphagnum lindbe gii, Chlo ophyll, UVB, Pea lands © 2015 Hyy yläinen e al. This a icle is dis ibu ed unde he e ms o he C ea i e Commons A ibu ion 4.0 In e na ional License (h p://c ea i ecommons.o g/licenses/by/4.0/), which pe mi s un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided you gi e app op ia e c edi o he o iginal au ho (s) and he sou ce, p o ide a link o he C ea i e Commons license, and indica e i changes we e made. Backg ound Sphagna a e c ucial in o ming and sus aining pea - lands—speci ic ecosys ems ha main ain a unique di e - si y o habi a s and species (Clymo and Haywa d 1982; Vi 2000; Rydin e al. 2006; Rydin and Jeglum 2006) and unc ion as a la ge s o e o o ganic ca bon, pa icula ly in bo eal and suba c ic a eas (Go ham 1991; Limpens e al. 2008). As a key componen o he ecosys em, hey a ec many p ocesses wi hin i ; he e o e, he changes igge ed in Sphagna by a changing en i onmen may be e lec ed in he en i e ecosys em. This is impo an , as hey a e also suscep ible o changes in he en i onmen , including shi s in UVB and empe a u e egime (e.g. Do epaal e al. 2003; Hu unen e al. 2005; Wiede mann e al. 2007; Gignac 2011), p incipally due o hei spe- ci ic s uc u e (lea es o one cell laye , absence o waxes o any o he p o ec i e su ace s uc u es). In open pea - lands, Sphagnum mosses a e no shielded by ee cano- pies and can be exposed o high le els o UVB i adiance. Gi en he impo ance o Sphagna o he sus ainabili y o pea lands, conside ing ecen inc eased sola UVB i a- diance (Wea he head e al. 2005) and ele a ed empe a- u es a high la i udes (Jylhä e al. 2004; McBean 2005), i is essen ial ha we unde s and how bo h hese ac o s a ec pea mosses. Sola UV adia ion is an impo an en i onmen al ac- o , egula ing g ow h, biochemis y and some s uc u al ea u es in b yophy es (Geh ke 1998; Rozema e al. 2005; Caldwell e al. 2007). UV e ec s on mosses a e species- speci ic, possibly e lec ing di e ences in desicca ion ol- e ance (Csin alan e al. 2001). Sphagnum mosses g owing unde nea -ambien condi ions seem o be able o hold mo e wa e as hey a e sho e and s ou e , and ha e Open Access *Co espondence: anna.koi uleh [email protected] 1 Depa men o Biology, Uni e si y o Oulu, P.O. Box 3000, 90014 Oulu, Finland Full lis o au ho in o ma ion is a ailable a he end o he a icle Page 2 o 11 Hyy yläinen e al. Sp inge Plus (2015) 4:478 la ge capi ula, han hose g owing unde a enua ed UVB (Robson e al. 2003, 2004). Changes in he in ensi y o di e en wa eleng hs o sola i adiance a ec shape and size o chlo oplas s (Glime 2007), as well as pigmen concen a ion in b yophy es (Niemi e al. 2002a, b). E en a small enhancemen (by less han 1°C) o sum- me empe a u es may ha e a signi ican e ec on g ow h and co e densi y o pea mosses (Do epaal e al. 2003). These esponses a e species-speci ic, and seem o co e- la e wi h he equi emen s o a pa icula species o en i- onmen al condi ions (Gunna sson e al. 2004; B eeuwe e al. 2008; Ha aguchi and Yamada 2011). Di e ences in esponses o inc eased empe a u es may, in he long un, lead o changes in species composi ion in a gi en ecosys- em. Whe e inc eased empe a u es do no di ec ly a ec pea mosses, hey may s ill ha e an impac on ascula plan s (Wel zin e al. 2000). As a consequence, species ange and a io may change, and ha may be haza dous o he ecosys em. The pho osyn he ic pigmen s in Sphagna a e chlo o- phyll a and b, and ca o enoids. The abso p ion spec a o he wo chlo ophylls (chls) di e sligh ly (Po a e al. 1989), and plan s use hese di e ences o adap o a y- ing ligh condi ions. In mosses, he o al chl con en and a/b a io changes depending on ac o s such as ligh a ailabili y, plan i ali y, g ow h phase, and a ious en i- onmen al s esses (Bax e e al. 1992; Ma ínez-Abaiga e al. 1994; Ge dol 1996; Ma ínez-Abaiga and Núñiez- Oli e a 1998; Bonne e al. 2010). A de ici o ligh o en p omo es chl b p oduc ion, educing he chl a/b a io. To al chl con en is gene ally highe in species ha g ow in shady habi a s, and lowe in hose commonly ound in open sunny si es (Ma in and Chu chill 1982; Ma ínez- Abaiga and Núñiez-Oli e a 1998). Du ing he g owing season, he chl con en no mally inc eases wi h dec eas- ing ligh in ensi y. Seasonal pigmen a ia ion is mo e p onounced in species g owing in a ying ligh condi- ions, han hose g owing in pe manen ly shady o sunny habi a s (Ke shaw and Webbe 1986; Ma ínez-Abaiga and Núñiez-Oli e a 1998). In Sphagna, chl con en is species-speci ic (Geh ke 1998; Niemi e al. 2002a, b) and i depends on he ecological equi emen s o he species (Ye emo e al. 2000; Naumo and Kosykh 2011). Nigh chilling may cause apid deg ada ion o chls in some Sphagna (Ge dol e al. 1994). In Sphagnum mosses, a posi i e co ela ion be ween chl concen a ion and ne pho osyn hesis has been eco ded (Gabe ščik and Ma inčič 1987). Thus, en i on- men al ac o s a ec ing he chl con en in pea mosses may also a ec he a e o pho osyn hesis. B yophy es om open sunny habi a s a e no mally adap ed o pho- osyn hesise unde in ensi e sunligh , some eaching Pmax a ~1000µmolm−2 s−1 and dissipa ing ex ensi e ene gy by non-pho ochemical quenching, NPQ (P oc- o 2000). Howe e , hose species in open en i onmen s o en expe ience wa e de ici . On he o he hand, b yo- phy es om shady o es si es a e adap ed o li e unde as li le as~100–300µmolm−2 s−1 bu mo e a ely ha e o sus ain d ough . In his sense, Sphagna species ypi- cal o lawns and ca pe s o open bogs ha e a e y spe- ci ic posi ion, as hey g ow unde in ensi e ligh usually ye wi h no wa e de ici . Howe e , Sphagnum species o open pea lands a e epo ed o ha e lowe pho osyn- he ic capaci y and maximum quan um yield han hose ha g ow in he shade (Hájek e al. 2009). Syne ge ic e ec s o sola UV wi h o he co- a ying en i onmen al ac o s in b yophy es may be mo e p o- nounced (Sonesson e al. 2002; Rinnan e al. 2013) o e en opposi e (Bjö n e al. 1999) o hose o UV alone. Howe e , s udies o such combined e ec s a e sca ce. Li le is known abou esponses o di e en Sphagnum species o simul aneous changes in sola UV and em- pe a u e egime o e a p olonged pe iod o ime (Son- esson e al. 2002; Aphalo 2003). UVB a enua ion may ha e simila e ec s on pea mosses as inc eased summe empe a u es, ha include e.g. inc easing leng h inc e- men and simul aneously dec easing he bulk densi y o moss co e (Do epaal e al. 2003; Robson e al. 2003, 2004). To s udy he impac o UVB and empe a u e on pea mosses, we conduc ed an open ield expe imen on a la k en in no he n Finland. We aimed o s udy how changes in bo h UVB and empe a u e egime a ec con- cen a ions o chl a and b, and hei a io in h ee Sphag- num species: S. bal icum, S. jensenii and S. lindbe gii. Al hough a ying in co e age, hese we e he mos com- mon pea moss species on he expe imen al si e. We hypo hesized ha unde a enua ed sola UVB and sligh ly ele a ed empe a u e chlo ophyll p oduc ion in Sphagnum mosses would inc ease. We sugges ed ha UVB-a enua ion plo s migh p o ide he mos a ou - able condi ions o plan g ow h, because o he elease o appa en nega i e UVB e ec s and a pa allel inc ease in empe a u e. Addi ionally, he polyes e il e s used o c ea ing −UVB condi ions pa ly ansmi UVA, which may ha e posi i e e ec on plan s (Niemi e al. 2002b). Hence, we expec ed a highe chlo ophyll concen a ion in he mosses g owing in he UVB-a enua ion plo s. Me hods The UVB a enua ion expe imen ook place in no h- e n Finland on a emo e oligo ophic all-sedge Sphag- num la k en, in Kal io uoma, Vuo so, abou 200 km om Pola Ci cle [263 m a.s.l., 68˚10′N, 26˚42′E (75649:34878)] (Soppela e  al. 2006). This open ield expe imen was a pa o he ECOREIN p ojec (The eco- logical and socioeconomical esponses o global change Page 3 o 11 Hyy yläinen e al. Sp inge Plus (2015) 4:478 on eindee pas u es). The e o e, he expe imen al si e ep esen ed a ypical eindee summe pas u e, whe e pea mosses domina ed in he g ound laye , mos abun- dan being S. lindbe gii, S. jensenii, S. angus i olium, and S. bal icum. The ield laye was cha ac e ized by sedges (E iopho um usseolum, E. angus i olium, Ca ex o unda a, C. os a a, C. limosa, C. magellanica subsp. i igua, Scheuchze ia palus is), he bs (Menyan hes i- olia a, Rubus chamaemo us) and sh ubs (And omeda poli olia, Be ula nana, Vaccinium oxycoccus, V. mic o- ca pum). Chemical analysis o he uppe subs a e laye (0–30 cm) ga e he ollowing esul s: pH 4.2, ca bon ( o al o ganic ca bon) 41.5%, ni ogen 0.64%, ca bon/ ni ogen a io 65, ammonium (NH4) 82.9mgkg−1, ni a e (NO3) <0.2 mg kg−1 and ammonium-lac a e ex ac ed (i.e., plan -a ailable) nu ien s: phospho ous 45mgkg−1, calcium 1.680 mg kg−1, magnesium 568 mg kg−1 and po assium 133mgkg−1 (Soppela e al. 2006; Ma z e al. 2009). Expe imen al design In 2001, a si e o abou one hec a e was enced o on he a ea, o p o ec i om eindee . In 2002, 30 andomly a anged plo s we e es ablished on he si e (Fig.1). Each plo was su ounded by a wooden ame (100×100cm). Th ee ea men s we e used in he expe imen : (1) a en- ua ed UVB (−UVB) plo s, wi h ames co e ed by a clea polyes e ilm, 0.125mm hick (Poli oil, KTA L d., Hel- sinki, Finland), (2) con ol plo s, co e ed wi h a clea sol en cas ace a e ilm (Cla i oil, De by, UK), and (3) ambien plo s whe e ames we e no co e ed. Each ea - men was eplica ed en imes. The polyes e ansmi - ed less han 1% o UV adia ion below 315nm, 30% a 320nm and abou 70% abo e 330nm, while he cellulose ace a e il e ansmi ed i adiance abo e 290nm e i- cien ly bu less han 1% o UV adia ion below 290nm (Soppela e al. 2006). Howe e , due o di use adia ion, ac ual UVB alues eaching he mosses unde he il e s we e highe . Unde he polyes e il e s he adia ion was on a e age 20% and unde cellulose ace a e il e s abou 72% o ha in ambien plo s (12.1± 0.3 uW/cm2 in –UVB, 42.1±1.1 uW/cm2 in con ol, and 58.6±3.1 uW/ cm2 in ambien plo s, mean±SE). Ambien UV i adiance was measu ed wi h a spec o- pho ome e B ewe MKII (SCI-TEC, Canada), ins alled on he oo o a building a he A c ic Resea ch Cen e o he Finnish Me eo ological Ins i u e (FMI-ARC) in Täh elä, Sodankylä (67˚22′N, 26˚38′E), as desc ibed in Ma z e  al. (2007). The ambien biologically e ec i e UVB (UV-BBE) i adiance was calcula ed acco ding o Caldwell e al. (1980), and e e s o UV-BBE calcula ed wi h he gene alized plan ac ion spec um (Caldwell 1971) (Fig.2a). We also pe o med UVB measu emen s in he ield in 2008, while sampling, using a po able me e AIRAM UVM-8 (Ka a Tekniikka Oy, Helsinki), equipped wi h a UVM-8B senso (wa eleng h a ea: 270– 370nm, max sensi i i y 310nm) (Fig.2b). Addi ionally, Fig. 1 View o some o he plo s and he walkway in he UVB a enu- a ion expe imen in Vuo so, no he n Finland b a Fig. 2 a Sola UV-BBE daily maxima in 2007–2008 (FMI, Sodankylä). b Sola UVB i adiance measu ed in Vuo so expe imen al si e in 2008. The labels p esen mean da a ±1 SD Page 4 o 11 Hyy yläinen e al. Sp inge Plus (2015) 4:478 we measu ed he pH o he subs a e wa e wi h a po - able pH me e (Tes o 206, Lenzki ch, Ge many) (Fig.3). Each plo was equipped wi h a po able empe a u e da alogge (Tiny Talk II, −40 o 75°C; OTLM So wa e, O ion Componen s, L d., Chiches e , UK), a ached o he cen al pole abou 15cm below he il e and 15cm abo e he su ace o he Sphagnum laye a he begin- ning o each g owing season. Tempe a u e was eco ded e e y 1.5h. Due o he ilm co e , he empe a u e in −UVB and con ol plo s inc eased up o 1°C, compa ed o he ambien plo s. The a e age empe a u e o he pe iod o eco d in 2008 (14 h June–27 h Augus ) was 13.8±0.09°C in ambien , 14.8±0.09°C in con ol, and 14.5±0.09°C in –UVB plo s (mean±SE). Di e ences in empe a u e among he h ee ea men s we e s a is i- cally signi ican (F2,26=30.5, p<0.001). E e y yea we e-ins alled he ames a he si e, adjus - ing new plas ic il e s in May–June, as soon as wea he condi ions allowed access o he expe imen al si e, bu be o e he plan s s a ed o g ow. Du ing he g owing season, he ames we e g adually aised, o allow he all- es sedges o g ow eely unde he ilms. The il e s we e also sligh ly ele a ed in he cen e by a e ical pole so ha he ainwa e d ained o he sides, keeping he il e d y. No addi ional wa e was gi en o he plo s, because e en in a e y d y summe he wa e able in he en emains s able (Fig.4). The expe imen al pe iods we e as ollows: 6 June–5 Sep embe 2002 (91days), 19 May–3 Sep embe 2003 (107days), 17 June–6 Sep embe 2004 (81days), 29 June–9 Sep embe 2005 (72days), 31 May– 18 Sep embe 2006 (110days), 16 June–20 Sep embe 2007 (96days), 14 June–28 Augus 2008 (74days). Sampling andmeasu emen s Fo chlo ophyll analysis, we chose S. lindbe gii, S. jensenii, and S. bal icum, which make up, espec i ely 87, 5 and 3% o he g ound co e in he expe imen al plo s (co e pe cen ages calcula ed as a mean alue om he 30 sam- ple plo s). We sampled S. lindbe gii (n=8–10 samples pe ea men ) in 2007 (12 July, 26 July, 23 Augus , 27 Sep embe ) and 2008 (13 June, 3 July, 24 July, 28 Augus ) o ollow bo h seasonal and yea - o-yea changes in chlo- ophyll concen a ion. Each sample is a pooled sample o 10 capi ula collec ed om each o he 30 expe imen al plo s. When analysing yea - o-yea changes in chl con- cen a ion, di e ences in he sampling da es be ween he 2yea s had o be aken in o accoun . To analyse in e - species and seasonal a ia ion, we also collec ed S. bal- icum and S. jensenii (n=5–10 pe ea men , due o smalle co e age o he species in he plo s) in 2008 (3 July, 24 July, 28 Augus ). The samples we e immedia ely imme sed in liquid ni ogen and anspo ed o he labo- a o y o he Na u al Resou ces Ins i u e Finland (Luke) in Ro aniemi. The ma e ial was kep in a supe eeze (−80°C) p io o analysis. I was hen lyophilized and g ound. Exac ly 15mg (DW) o each sample we e scaled, and used o chlo ophyll ex ac ion wi h pu e me hanol (1.5ml pe sample) in 24h, a +4°C, in he da k. The abso bance o he me hanol ex ac was measu ed a 652.0, 665.2 and 750nm wi h a spec opho ome e (Shi- madzu-1700), and he concen a ion o chlo ophyll a and b, and o al chlo ophyll (µgml−1) was calcula ed ollow- ing Po a e al. (1989). S a is ical analysis The da a we e analysed by he means o linea mixed models in which he sampling da e was aken as he Fig. 3 pH measu emen s in he ield showed ha subs a e acidi y did no signi ican ly di e in di e en ea men s. Values a e es i- ma ed ma ginal means ± 90 % con idence in e als Fig. 4 No addi ional wa e was gi en o he plo s, because e en in a e y d y summe he wa e able in he en emains s able unde hese cool and humid condi ions. Ca ex sp., Menyan hes i olia a and Sphagna seen in he pic u e seem o g ow s aigh on wa e Page 5 o 11 Hyy yläinen e al. Sp inge Plus (2015) 4:478 epea ed ac o . In cases whe e he chlo ophyll concen- a ions o all he h ee species we e compa ed, bo h he species and he ea men we e ixed ac o s. The species was no aken as a ac o when analysing chlo ophyll con- cen a ion in S. lindbe gii alone, and subs a e pH unde di e en ea men s. Due o he epe i i e sampling om he same plo s he da a con ained a co ela ion s uc u e. The co a iance s uc u e o he epea ed ac o was he - e ogeneous i s -o de au o eg essi e (ARH1), which was selec ed on he basis o he lowes Akaike’s in o ma ion c i e ia (AIC) alue. Fo linea mixed models, Es ima ed Ma ginal Means (EMMEANS) and 90 % con idence in e als we e compu ed, and a e p esen ed in Figs.3, 5 and 6. Hence, hose means wi h non-o e lapping con idence in e als a e s a is ically signi ican ly di e en (a p<0.05; Figs.3, 5, 6). Co ela ions be ween en i on- men al and chlo ophyll concen a ion da a we e com- pu ed as Pea son’s co ela ion coe icien s (Addi ional iles 1, 2). Co ela ions be ween he chlo ophyll con en and subs a e pH we e compu ed as Spea man’s co ela- ion coe icien s. S a is ical analyses o he da a we e pe - o med using IBM SPSS S a is ics 19.0. Resul s Seasonal andin e ‑annual a ia ion P io o sampling, he h ee co-exis ing Sphagnum spe- cies g ew unde a enua ed UVB and enhanced empe a- u e condi ions o six g owing seasons (2002–2007). We a b c Fig. 5 Seasonal a ia ion o o al chlo ophyll con en in a Sphagnum bal icum, b S. jensenii and c S. lindbe gii unde ambien (open ba s), con- ol (da k g ey ba s) and −UVB ea men (ligh g ey ba s). Fo S. lindbe gii, he da a o 2007–2008 a e shown. Values a e es ima ed ma ginal means ± 90 % con idence in e als Page 6 o 11 Hyy yläinen e al. Sp inge Plus (2015) 4:478 de ec ed signi ican species-speci ic seasonal a ia ion in chlo ophylls a, b, a+b, and chl a/b in hese species du - ing he expe imen (2007–2008, Figs.5, 6; Table1). The e was also signi ican in e -annual a ia ion in Sphagnum lindbe gii (Tables1, 2; Figs.5c, 6). In 2008, concen a ion o chlo ophyll in he dominan S. lindbe gii inc eased sha ply om e y low concen- a ions in mid-June o be ween wo and six imes ha amoun by July, hen emained ai ly s able o he es o he season. In bo h S. jensenii and S. bal icum, chlo- ophyll concen a ion dec eased signi ican ly owa ds he end o he summe in all he ea men s (Fig.5). S. bal i- cum had signi ican ly lowe chlo ophyll alues han he o he wo species. In S. lindbe gii, chlo ophyll concen a ion was no ice- ably lowe in 2007 compa ed o 2008 (Fig.5c). I also a ied signi ican ly du ing he g owing season o 2007, being highes in July, dec easing a he end o summe Fig. 6 In e annual a ia ion o chlo ophyll a/b a io in S. lindbe gii unde ambien (open ba s), con ol (da k g ey ba s) and −UVB ea men (ligh g ey ba s). Values a e es ima ed ma ginal means ± 90 % con idence in e als Table 1 E ec o UVB ea men , species, andsampling da e onconcen a ion o chlo ophyll a andb, o al chlo ophyll (a+b) anda/b a io Fo each e ec and hei in e ac ions F alues and s a is ical signi icance o mixed linea model analysis a e p esen ed Sou ce Chl aChl bChl a + bChl a/b F p alue F p alue F p alue F p alue T ea men 4.3 0.017 2.8 0.067 3.8 0.025 0.5 0.636 Species 52.1 <0.001 63.8 <0.001 56.4 <0.001 13.4 <0.001 Da e 90.7 <0.001 79.9 0.000 90.8 <0.001 7.3 <0.001 T ea men × species 1.0 0.391 0.7 0.620 0.8 0.500 0.4 0.776 T ea men × da e 3.4 0.003 2.3 0.037 3.2 0.005 1.7 0.124 Species × da e 11.1 <0.001 7.2 <0.001 10.1 <0.001 8.3 <0.001 T ea men × species × da e 2.0 0.050 1.6 0.127 1.8 0.088 4.7 <0.001 Table 2 E ec o UVB ea men andsampling da e onconcen a ion o chlo ophyll a andb, o al chlo ophyll (a+b) anda/b a io inSphagnum lindbe gii Fo bo h e ec s and hei in e ac ion F alues and s a is ical signi icance o mixed linea model analysis a e p esen ed Sou ce Chl a Chl b Chl a+b Chl a/b F p alue F p alue F p alue F p alue T ea men 0.69 0.504 0.43 0.65 0.59 0.559 4.97 0.01 Da e 66.7 <0.001 55.4 <0.001 64.5 <0.001 47.4 <0.001 T ea men × da e 2.16 0.03 1.81 0.07 2.13 0.032 1.48 0.158 Page 7 o 11 Hyy yläinen e al. Sp inge Plus (2015) 4:478 and inc easing again in Sep embe . The chl a/b a io in his species was signi ican ly lowe in 2007 han in 2008 (Fig.6). T ea men e ec s Th oughou he expe imen , combined empe a u e and UVB manipula ion had only mino e ec s on he chosen Sphagnum species in his habi a , and hese e ec s we e da e-dependen (Tables 1, 2; ea men e ec includes bo h UVB and empe a u e manipula ion). A ansien UV e ec was de ec ed on he 3 d July 2008 in S. lind- be gii as a highe chl a+b concen a ion in he plan s unde con ol condi ions, compa ed o hose in he UVB- a enua ed ea men (Fig.5c). A signi ican empe a u e e ec was obse ed in S. lindbe gii in 2008 (Figs.5c, 6). By he end o he g owing season in 2007 (27 h Sep embe ), plan s unde di e en ea men s had app oxima ely he same concen a ion o o al chlo ophyll and chl a/b a io. Howe e , when he nex season s a ed (13 h June 2008), chlo ophyll concen a ion and a/b a io inc eased signi ican ly in only he ambien plo s, while in he plan s unde he il- e s hese pa ame e s emained a he le el o he p e- ious yea . By con as , la e in he season o 2008, he chlo ophyll concen a ion inc eased sha ply ( ou –six old) in S. lindbe gii unde he il e s, while in ambien condi ions less so ( wo old). The chl a/b a io in his species emained s able in ambien condi ions o he whole g owing season in 2008, while in he plo s wi h inc eased empe a u e he a io was signi ican ly lowe a he beginning o he season (Fig.6). Addi ionally, he empe a u e e ec was obse ed in S. lindbe gii on 23 d Augus 2007, as a highe chl a/b in ambien compa ed o con ol plo s. Discussion Seasonali y in physiological cha ac e is ics is ypi- cal o b yophy es, oge he wi h wide a ia ion in ligh esponses be ween he species (P oc o 2000). Whe e ligh in ensi y a ies subs an ially du ing he g owing season ( o example, in a deciduous o es —due o can- opy closu e), chlo ophyll con en and chl a/b a io in mosses change no iceably in line wi h ligh a ailabili y. In open pea lands, by con as , Sphagnum mosses expe i- ence ela i ely high i adiance, which emains s able o a p olonged pe iod o ime. This may explain why in S. lindbe gii, bo h o al chlo ophyll concen a ion and chl a/b a io we e ai ly s able in July–Augus 2008 (Figs.5c, 6). This is in compliance wi h he esul s ound by Mish- le and Oli e (1991) in hei s udy o b yophy es in open sunny habi a s. Highe and mo e s able o al chlo ophyll concen a ion and highe chl a/b a io in S. lindbe gii in 2008 compa ed o 2007 could ha e been due o highe (253mm in 2008 s. 220mm in 2007) and mo e e enly dis ibu ed p ecipi a ion du ing summe ha yea (FMI 2007–2008) (Fig.7a). An inc ease in o al chl wi h dec easing ligh in ensi y and day leng h may be expec ed in au umn (Ke shaw and Webbe 1986; Niemi e al. 2002b), as we eco ded om he samples o S. lindbe gii in au umn 2007. Howe e , in S. bal icum and S. jensenii, he o al chl con en ell a he end o he g owing season, as consis en wi h he indings o Lappalainen e al. (2008) and Ge dol (1996). These spe- cies wi h low co e age on he si e ha e mo e speci ic sub- s a e equi emen s. S. bal icum is usually ound on e y poo omb o ophic bogs wi h subs a e pH<4.5, while S. jensenii al hough g owing a wide pH ange (4.1–5.9), p e e s mo e mine o ophic condi ions o poo and in e - media e ens (Woj uń e al. 2013). The dominan S. lind- be gii is compa a i ely lexible, success ully g owing in a wide a ie y o ophic condi ions, om omb o- o min- e o ophic si es, wi h pH o he subs a e anging wi hin ca. 4.0–5.8 (Gunna sson e al. 2004; Laine e al. 2009; Woj uń e al. 2013). In he la e species, he chlo ophyll concen a ion did no dec ease a he end o he g owing season in 2008. The di e ences be ween he species a e clea ly seen when analysing co ela ion be ween chlo o- phyll con en and pH o he subs a e wa e . A signi ican nega i e co ela ion was ound be ween he con en o chl a and chl b and subs a e pH in bo h S. bal icum and S. jensenii, whe eas in S. lindbe gii chl con en did no seem o be co ela ed wi h pH in none o he ea men s (Table3). Tempe a u e and ligh in ensi y oge he a ec pho o- syn he ic a es in mosses (P oc o 2011), and hus may ha e po en ial o a ec chlo ophyll con en in Sphagna; empe a u e e ec s on pho osyn he ic pigmen s in pea mosses depend on ligh in ensi y (Ha aguchi and Yam- ada 2011). Ce ain Sphagnum species a e adap ed o ha e high pho osyn he ic a es a high empe a u es and in ensi e ligh , o a low empe a u es and low ligh le - els. Low empe a u es a high ligh in ensi y may ha e a nega i e e ec on hei pho osyn hesis (Ha aguchi and Yamada 2011) and may ha e been one o he easons o low chlo ophyll con en obse ed in S. lindbe gii in mid June 2008. Low chlo ophyll con en a he beginning o he season migh also be due o ac i e g ow h, when shoo s a e g owing as , and chlo ophyll biosyn hesis a es do no ma ch hose o shoo g ow h (Ke shaw and Webbe 1986). La e in he season, in ensi e ligh com- bined wi h high ambien empe a u e may explain he inc ease in o al chlo ophyll in S. lindbe gii (Fig.7). Du ing his expe imen , he species-speci ic seasonal changes in chlo ophyll concen a ions obse ed we e mo e p onounced han he ea men e ec s (Table4). The s udied pea mosses, coexis ing in he same habi a , Page 8 o 11 Hyy yläinen e al. Sp inge Plus (2015) 4:478 a b1 b2 c Fig. 7 En i onmen al da a: a P ecipi a ion in June–Augus 2007–2008 (FMI, Sodankylä). b Tempe a u es, measu ed du ing he g owing season in he expe imen al si e in Vuo so. Mean, maximum and minimum alues in di e en ea men s a e shown. c Daily sum o ne adia ion, no mal- ized, kJ/m2 (FMI, Sodankylä). Ve ical lines poin he sampling da es (dashed o 2007, solid o 2008) Page 9 o 11 Hyy yläinen e al. Sp inge Plus (2015) 4:478 showed qui e uni o m esponse o expe imen ally al e ed condi ions, bu di e ed in hei esponses o na u al sea- sonal changes in ligh and empe a u e egime. Tempe a- u e and UVB manipula ion we applied seemed o play a lesse ole in plan acclima ion han ecophysiological cha ac e is ics o a species, he unique combina ion o i s niche equi emen s. In he gi en condi ions, S. lindbe - gii seemed o be able o acclima e o a wide spec um o en i onmen al condi ions, and o wi hs and en i onmen- al changes be e han he mo e omb o ophic S. bal- icum o mo e mine o ophic S. jensenii (Gignac 2011). I is possible ha he abili y o sus ain he le el o chlo- ophyll du ing he g owing season is one o he ea u es ha helps S. lindbe gii o keep i s dominan posi ion, compa ed o he o he wo Sphagna, in he gi en habi a . Ini ially we hypo hesized ha Sphagnum mosses g ow- ing in he UVB-a enua ion plo s would ha e highe chlo ophyll con en as compa ed o he mosses in he ambien o con ol condi ions. Howe e , measu emen s e ealed a highe chlo ophyll concen a ion and chl a/b a io in S. lindbe gii sampled om ambien plo s a he beginning o he season in 2008. This may be due o be e o e win e ing abili ies and highe pho osyn he ic ac i i y in he plan s in ambien condi ions compa ed o hose g owing unde inc eased empe a u es (Gun- na sson e al. 2004). Highe o al chlo ophyll con en in S. lindbe gii in he con ol compa ed o −UVB plo s on 3 d o July 2008 may also be explained by he highe UVA adia ion doses unde cellulose ace a e il e s. A he end o he g owing season in 2008, we de ec ed no s a is ical di e ences be ween he ea men s; ins ead, he e we e signi ican di e ences among he species in each ea men . This indica ed ha i was no he changes in empe a u e and UVB i adiance ha a ec ed he chlo ophyll seasonali y mos , bu a he species adap - abili y and hei habi a equi emen s. Conclusions A sligh empe a u e inc ease and/o a signi ican a enu- a ion o sola UVB adia ion ( o less han 1% o he ambi- en ) had no clea e ec on he chlo ophyll concen a ion o i s seasonal a ia ion in he Sphagnum species g owing in an open en. Al oge he , he species s udied seemed o be adap ed o he changes in he en i onmen hey we e Table 3 Co ela ion be weenpH o  he subs a e andchlo ophyll con en in he h ee co-exis ing Sphagnum species inambien andexpe imen ally al e ed empe a u e andUVB condi ions *Co ela ion is signi ican a he 0.05 le el (2- ailed) **Co ela ion is signi ican a he 0.01 le el (2- ailed) pH ina ea men S. bal icum S. jensenii S. lindbe gii Chl aChl bChl aChl bChl aChl b Ambien Spea man’s ho −.506** −.535** −.522** −.494** .150 .055 p alue .008 .005 .004 .007 .446 .781 N26 26 29 29 28 28 Con ol Spea man’s ho −.464* −.630** −.607** −.566** −.189 −.308 p alue .030 .002 .000 .001 .327 .105 N22 22 29 29 29 29 –UVB Spea man’s ho −.449* −.594** −.404* −.326 .167 .217 p alue .024 .002 .041 .105 .387 .259 N25 25 26 26 29 29 Table 4 Co ela ions (Pea son co ela ion coe icien s) be ween he o al chlo ophyll concen a ion (Chl) o  he h ee s udied species and empe a u e andUVB on he h ee di e en da es he UVB was measu ed andsamples collec ed The empe a u e is he daily mean o he p eceding da e. S a is ically signi ican (p<0.05) co ela ion coe icien s ma ked wi h as e isk Da e Chl inS. bal icum Chl inS. jensenii Chl inS. lindbe gii Tempe a u e UVB Tempe a u e UVB Tempe a u e UVB 3.7.2008 .238 −.169 .193 .148 .282 .431* 24.7.2008 .076 −.240 −.349 .351 .220 −.129 28.8.2008 −.214 .352 −.055 .092 .005 −.036