Early snowmelt enhances the carbon sequestration of hummock-forming Sphagnum mosses on boreal wetlands

OpenJou nalo Ecology,2016,6,103‐112 PublishedOnlineFeb ua y2016inSciRes.h p://www.sci p.o g/jou nal/oje h p://dx.doi.o g/10.4236/oje.2016.63011 How oci e hispape :Sil an,N.andJokinen,K.(2016)Ea lySnowmel Enhances heCa bonSeques a iono Hum‐ mock‐Fo mingSphagnumMossesonBo ealWe lands.OpenJou nalo Ecology,6,103‐112. h p://dx.doi.o g/10.4236/oje.2016.63011 Ea lySnowmel Enhances heCa bon Seques a iono Hummock‐Fo ming SphagnumMossesonBo ealWe lands NikoSil an1*,Ka iJokinen2 1Na u alResou cesIns i u eFinland,Na u alResou cesandBiop oduc ion,Pa kanoUni ,Pa kano,Finland 2Na u alResou cesIns i u eFinland,Na u alResou cesandBiop oduc ion,ViikkiUni ,Helsinki,Finland   Recei ed16Sep embe 2015;accep ed12Feb ua y2016;published15Feb ua y2016 Copy igh ©2016byau ho sandScien i icResea chPublishingInc. Thiswo kislicensedunde  heC ea i eCommonsA ibu ionIn e na ionalLicense(CCBY). h p://c ea i ecommons.o g/licenses/by/4.0/    Abs ac  Sphagnummossesa egloballyimpo an owing o hei conside ablepea ‐ o mingabili yand hei po en ialimpac onglobalclima iccyclesac ingasalong‐ e mne ca bonsink.Howe e , changesinclima iccondi ionsdue oglobalwa mingmaya ec  he ela ionsbe weenSphagnum mossesand ascula plan sbu also hecompe i ionamongSphagnum,and husal e  heaccu‐ mula iono ca bononbo ealwe lands.Sphagnummossesa eaplan genuswi ha a o ableabil‐ i y og owinlowsola i adianceand empe a u econdi ionscompa ed o ascula plan s.This maybeinc easinglybene icialininc easedwin e ime empe a u esandp eda edsnowmel  condi ions.Tounde s andpa icula ly heimpo anceo ea lysp ingpho osyn he icac i i yand hus he oleo  heleng ho g owingseasononca bonbalance,weanalyzed heCO2exchangeo  Sphagnummosseswi hclosedchambe  echniquein woca ego ieso mic o opog aphicalhabi‐ a s,hummocksandlawns,du ing ou seasons2010‐2013ona aisedboginCen alFinland. Du ingCO2exchangemeasu emen s,ins an aneousne ecosys emexchange(NEE)andecosys em espi a ion(RE)we emeasu ed.Ou  esul sshow ha  hemeanmeasu edseasonalNEE,i.e. he ins an aneousne ca bonseques a ion,o hummockswasgene allyonlysligh lyhighe  han he NEEo lawns,bu  hemeanmeasu edseasonalREo hummockswasclea lyandsigni ican ly highe  han heREo lawnsine e ys udyyea .A eason o  heobse eds illhighe seasonal ca bonseques a iono hummocks han ha o lawnsbesides hesligh lyhighe  a eo ca bon accumula ionwas helonge du a iono physiologicallyac i eg owingseason.The e o e,hum‐ mock‐ o mingSphagnummossesexposed i s ly omsnowco e showed oge  heex a ime o  pho osyn hesisand husex abene i compa ed oo he mi eplan s.Thismaybe u he en‐ hancedby heexpansiono hummock‐ o mingSphagnummossdomina ed aisedbogs owa ds no he naapa‐mi e egiondue o heglobalwa ming. *Co esponding au ho . N.Sil an,K.Jokinen 104 Keywo ds SphagnumMosses,Bo ealWe lands,Mi eMic o opog aphy,Ca bonDynamics,GlobalWa ming 1.In oduc ion Sphagnum moss species a e globally impo an owing o hei conside able pea - o ming abili y and hei po en- ial impac on global clima ic cycles [1] [2]. Sphagnum is he mos impo an pea o ming plan genus and he e may be mo e ca bon s o ed in Sphagnum han in any o he genus [3]. The genus Sphagnum includes 250 - 450 species, bu a he ewe han 50 species con ibu e o pea o ma ion on a la ge scale [4]. These pea -p oducing species a e mos abundan on bo eal we lands abo e la i ude 45N [5]. Thus, Sphagnum o ms a majo compo- nen o bo eal we lands, which co e 2% o he o al land a ea [6]. These we lands ha e ac ed as a long- e m ne ca bon sink and ake up 0.07 Pg ca bon pe yea [1] [7], equi alen o 5% o he o al ne ca bon lux om a - mosphe e o land [6]. Sphagnum mosses solely ha e hus been esponsible o he seques a ion o la ge quan i- ies o ca bon and play an impo an ole in he global ca bon cycle [8]. Changes in clima ic condi ions due o he global wa ming may a ec he ela ions be ween Sphagnum mosses and ascula plan s [9]. Changes in clima ic condi ions may also a ec compe i ion among Sphagnum, bo h h ough di ec mois u e changes and h ough he e ec s on Sphagnum densi y and g ow h a e [10] [11]. These may ha e impo an consequences o he long- e m s abili y o he mi e ege a ion communi y [12]. On bo eal we lands, ascula plan pe o mance is u he con olled by he p esence o Sphagnum, which o en domina es he bo om laye and he pea deposi s in which he plan s g ow [3]. Sphagnum mosses s ongly educe he a ailabili y o nu ien s o ascula plan s on nu ien -poo mi es by e icien ly accumula ing nu ien s om a - mosphe ic deposi ion and educing decay and mine aliza ion a es [9] [13]- [15]. A he same ime, howe e , hey o ce ascula plan s o keep pace wi h hei p og essi ely inc easing heigh , in o de no o become bu ied [9] [10] [16]. The e o e global wa ming may impac on he unc ioning o mi e ecosys ems ia al e a ions in species composi ion, and hus al e also he accumula ion o ca bon on bo eal we lands [8] [12] [17]. Acco ding o he six-yea s udy o Au ela e al. [18] on a suba c ic en in no he n Finland, he in e annual a ia ion o he CO2 balances o igina es almos comple ely om he a ia ions du ing he snow- ee pe iod. In hei s udy, he snowmel iming was p o en o be he mos impo an single de e minan o he annual ca bon balance. In con as o a commonly-held iew, he hyd ome eo ological condi ions du ing he g owing season had only a mino e ec on he annual balance, emphasizing he impo ance o he s a o he g owing season [18]. Sphagnum mosses ha e a a o able abili y o g ow in low sola i adiance and empe a u e condi ions compa ed o ascula plan s [19] [20]. In he s udy o Ha ley e al. [19], he pho osyn hesis o Sphagnum angus- i olium sa u a ed al eady in he pho osyn he ic pho on lux densi y (PPFD) unde 500 µmol·m−2·s−1. Pho osyn- hesis s a ed a ca. ±0˚C, when pho osyn he ic a es a 5˚C we e al eady ca. 50% o maximum and he sa u a ion empe a u e was a ca. 10˚C [19]. These equi emen s would no mally be me al eady in la e Ma ch a leas in sou he n and middle bo eal egion assuming ha no snow co e occu s. Bo eal aised bogs show a ypical pa e n o mic o opog aphical habi a s, anging om ela i ely d y bu egu- la ly (in sp ing a e snowmel ) inunda ed lawns o d y high hummocks (wi hou inunda ion pe iod), wi h a di - e en se o Sphagnum species occupying each mic ohabi a [21]. The e o e he dec ease in snow co e in ea ly sp ing migh be mo e bene icial o hummock- o ming Sphagnum species han o lawn species. This could enhance he expansion o hummock domina ed aised bogs owa ds no he n aapa-mi e egion due o he global wa ming. We hypo hesized he e o e 1) ha p oduc i i y o lawn species (e.g. S. allax and S. bal icum) will no in- c ease wi h dec easing snow co e , whe eas biomass p oduc ion o hummock species (e.g. S. uscum and S. magellanicum) will inc ease, and 2) ha global clima e wa ming wi h sho ened snow co e pe iod may hus p omo e a he han h ea en he ca bon seques a ion abili y o bo eal we lands by a o ing he g ow h o hummock- o ming Sphagnum. 2.Ma e ialsandMe hods 2.1.S udySi e The s udy was ca ied ou du ing 2010-2013 on a p is ine aised bog a Kauhane a, cen al Finland (62˚13'N, N.Sil an,K.Jokinen 105 22˚26'E). The mi e si e ype o he s udy si e was low sedge S. papillosum en wi h la ge Sphagnum hummocks [22]. The s udy si e lies in he ansi ional zone be ween sou he n-bo eal and middle-bo eal coni e ous o es zones, on he edge o a la ge aised bog a ea wi h he cha ac e is ics o bo h poo mine o ophy (lawns) and om- b o ophy (hummocks). The long e m (1983-2013) annual mean empe a u e o he si e was 3.8˚C, he annual mean p ecipi a ion 612 mm and he accumula i e empe a u e sum (>+5˚C) 1156 deg ee-days. The su ace o he s udy si e consis ed o a ypical pa e n o bo eal aised bogs: ela i ely d y bu egula ly inunda ed lawns o d y hummocks. The heigh o he s udied hummocks was ca. 0.4 m compa ed o he su - ounding lawn a ea. Soil o he si e consis ed o weakly decomposed Sphagnum-Ca ex pea wi h he dep h o ca. 1 me e . Dominan mosses on he hummock-plo s we e S. uscum and S. magellanicum, and on he lawn-plo s S. bal icum and S. allax. 2.2.Vege a ionMoni o ing A lea a ea index (LAI) es ima ion was employed in o de o ela e CO2 luxes o he spa ial and empo al a ia- ion in ege a ion. Fo ascula plan s, species-speci ic LAIs in each sample plo we e es ima ed in ea ly Augus du ing 2010-2013 as a p oduc o he numbe o lea es and he a e age lea size [23]. The numbe o g een lea es o each species was es ima ed by coun ing he numbe o he lea es in pe manen sub-sample plo s wi hin each sample plo ha accoun ed o 10% o he o al a ea o he plo . 2.3.CO2ExchangeMeasu emen s Six CO2 exchange measu emen plo s we e es ablished a he si e. Th ee o he measu emen plo s we e es ab- lished on he hummock su aces and he o he h ee on he lawn su aces. CO2 exchange measu emen occasions wi h closed chambe echnique [24] we e ca ied ou du ing he whole snow- ee pe iod (Ma ch/Ap il-Oc obe ) 2010-2013. The iming o snowmel was moni o ed a he si e, and CO2 exchange measu emen s we e s a ed in each sp ing immedia ely a e he snow co e was mel a leas om all o he hummock plo s. P io o measu emen s, an aluminium colla (60 × 60 cm) was pe manen ly inse ed in o 30 cm dep h in each plo . The colla was su ounded by a wa e g oo e ha allowed chambe placemen and ai - igh sealing o he measu emen sys em. Ins an aneous ne ecosys em CO2 exchange (NEE) in each plo was measu ed wi h a anspa en plas ic chambe and a po able in a- ed gas analyze (EGM-4, PP Sys ems, UK). Measu emen s o e 90 - 180 s we e ca ied ou in he ull ligh and unde an a i icial shade educing he ambien ligh by 40% - 60%. Du ing he measu emen s, he CO2 concen a ion in he chambe headspace, pho o syn he ically ac i e adia ion (PAR) unde he chambe oo , and he chambe empe a u e we e eco ded a 15-s in e als. A e he measu emen s in ligh , he chambe was co e ed wi h an opaque hood and he ecosys em espi a ion (RE) in he da k was measu ed. Wa e able le el (WTL) in a pe o a ed ube nex o each plo , and pea empe a u es a 5 cm below he moss su ace we e measu ed simul aneously wi h he CO2 exchange measu emen s o ela e he luxes o he p e ailing en i onmen al condi ions. NEE and RE we e calcula ed as he linea change in CO2 concen a ion as a unc ion o ime by i ing a linea eg ession line. 2.4.S a is icalAnalyses Since we had a limi ed amoun o da a on he CO2 exchange, we could no eliably model luxes on which o base simula ions o seasonal es ima es o NEE and RE. Ins ead, we concen a ed on es ing he signi icance o he e ec o mic o opog aphic habi a on ins an aneous NEE and RE, and in e pola ing he seasonal mean ca bon balances o bo h mic o opog aphical habi a s o e he g owing seasons. Since obse a ions we e made on he same measu emen plo s o e a pe iod o ime ( ou g owing seasons 2010-2013), he obse ed esponses we e he e o e co ela ed. As opposed o wo-way ANOVA, linea mixed models ha e been designed o handle co - ela ed da a wi h unequal a iances om no mal dis ibu ions [25]. Thus, he analyses o ins an aneous lux a es we e based on ixed e ec s models wi h es ic ed maximum likelihood es ima ion me hod using he linea mixed p ocedu e in SPSS S a is ics e . 22 (IBM Co p., USA). Tes esul s we e conside ed signi ican when p < 0.05. 3.Resul s 3.1.En i onmen alCondi ionsdu ing heS udyPe iod The he mal g owing season s a ed in la e Ap il o ea ly May and las ed un il he end o Oc obe du ing s udy N.Sil an,K.Jokinen 106 yea s 2010-2013 (Figu e 1). The mean seasonal (Ap il-Oc obe ) empe a u es a Kauhane a we e sligh ly highe in all s udy yea s 2010-2013 excep 2012 han he long e m a e age o 1984-2014 (10.5, 11.4, 9.4, 10.6 and 9.7˚C, espec i ely) (Figu e 1). Howe e , he mon hly empe a u es o ea ly season (Ap il-July) in 2010 and 2011 we e clea ly highe han he long e m a e age o 1984-2014 (Figu e 1). Pea empe a u es a 5 cm below he moss su ace measu ed simul aneously wi h he CO2 exchange measu emen s we e ypically close o 0˚C du ing he i s measu emen s a e snowmel and ose o hei seasonal maximum in July a ca. +20˚C (Figu e 2). Pea empe a u es in hummocks we e gene ally sligh ly highe han in lawns (Figu e 2). The highes pho osyn he ically ac i e adia ions (PAR) unde he chambe oo measu ed simul aneously wi h he CO2 ex- change measu emen s a ied om ca. 200 µmol·m−2·s−1 du ing la e season in Oc obe o 1600 µmol·m−2·s−1 du ing peak season in July (Figu e 3). Opposi ely, measu ed PAR alues we e du ing ea ly season in Ap il only ca. 20% lowe han du ing peak season in July (Figu e 3). The iming o snowmel a ied a he sligh ly du ing he s udy pe iod, occu ing ea ly Ap il in all s udy yea s excep 2012. Al hough he season o 2012 was he coldes du ing ou s udy pe iod 2010-2013, he snowmel was, howe e , he ea lies aking place in he middle o Ma ch in 2012. Sho - e m (ca. one mon h) inunda ion oc- cu ed immedia ely a e snowmel especially in sp ing 2010 on he lawn plo s (Figu e 2). The snow and/o in- unda ion ee pe iod las ed o se en mon hs co e ing he whole g owing season o he hummocks, whe eas only ca. six mon hs o he lawns ha ing he inunda ion a e he snowmel and delayed snowmel compa ed o hummocks. In 2012, he di e ence be ween hummocks and lawns in he snow and/o inunda ion ee pe iod was almos one and a hal mon hs. -10 -5 0 5 10 15 20 25 2010 2011 2012 2013 1983-2013 Ma Ap May Jun Jul Aug Sep Oc 0 50 100 150 200 Tempe a u e °C p ecipi a ion, mm Figu e 1. Mean ai empe a u e and mon hly p ecipi a ion a Kauhane a om Ma ch o Oc obe du ing 2010-2013 and as 30-yea a e age 1983-2013. N.Sil an,K.Jokinen 107 2010 Wa e Table Le el, cm -50 -40 -30 -20 -10 0 10 20 30 WTL Hummock WTL Lawn T5 Hummock T5 Lawn 2011 Tempe a u e -5cm, oC -50 -40 -30 -20 -10 0 10 20 30 2012 Ap May Jun Jul Aug Sep Oc No -50 -40 -30 -20 -10 0 10 20 2013 Ap May Jun Jul Aug Sep Oc No -50 -40 -30 -20 -10 0 10 20 Figu e 2. Measu ed wa e able le el (WTL) and soil empe a u e (T5) alues a 5 cm dep h below soil su ace a Kauhane a du ing 2010-2013. WTL and T5 alues based on manual measu emen s made in conjunc ion wi h CO2 exchange measu e- men s. Th ee WTL measu emen s om Ma ch-Ap il 2011-2013 a e missing because o he solid soil os . 2010 PAR  mol m-2 s-1 0 200 400 600 800 1000 1200 1400 1600 2011 2012 Ap May Jun Jul Aug Sep Oc No 0 200 400 600 800 1000 1200 1400 2013 Ap May Jun Jul Aug Sep Oc No Figu e 3. Measu ed pho osyn he ically ac i e adia ions (PAR) a Kauhane a du ing 2010-2013. PAR alues a e based on manual measu emen s made in conjunc ion wi h CO2 exchange measu emen s. Pa o he measu emen s was done unde an a i icial shade educing he ambien ligh by 40% - 60% esul ing he a he la ge a ia ion in PARs. N.Sil an,K.Jokinen 108 The cumula i e p ecipi a ions du ing Ap il-Oc obe we e a he close o he long- e m a e age o 1984-2014 (408 mm) in all s udy yea s 2010-2013 excep in 2012 (678 mm) (Figu e 1). Especially he mon hly p ecipi a- ions in July and Oc obe 2012 we e clea ly highe han he mon hly long e m a e ages o 1984-2014 (Figu e 1). Wa e able le els (WTL) measu ed in a pe o a ed ube nex o each CO2 exchange measu emen plo a ied om ca. −10 cm o −40 cm below he soil su ace o hummocks, and om ca. +10 cm abo e he soil su ace (inunda ion) in sp ing o −15 cm below he soil su ace o lawns (Figu e 2). In ea ly sp ing also solid soil os occu ed du ing he i s CO2 exchange measu emen occasions in 2011-2013, and he e o e WTLs canno be measu ed (Figu e 2). The maximum lea a ea index (LAI) o ascula plan s was gene ally e y low a Kauhane a, in a e age ca. 0.14 m2·m−2 o hummocks and ca. 0.17 m2·m−2 o lawns, espec i ely. The a ia ion in LAIs was e y small be ween he s udy yea s and he plo s. Dominan ascula plan s on he hummocks we e Empe um nig um, An- d omeda poli olia and Rubus chamaemo us, on he lawns E iopho um agina um, And omeda poli olia and Vaccinium oxycoccos, espec i ely. 3.2.CO2Exchange The mean measu ed seasonal NEE o hummocks du ing 2010-2013 was 329, 218, 201 and 162 mg CO2 m−2·h−1, espec i ely, and o lawns 220, 182, 240 and 156 mg CO2 m−2·h−1, espec i ely (Figu e 4). All mean seasonal NEE alues showed a posi i e seasonal ne balance, i.e. all measu ed CO2 exchange plo s ac ed as a sink o CO2 du ing 2010-2013, bu bo h mic o opog aphical habi a s showed ela i ely la ge di e ences in NEE be- ween he yea s (Figu e 4). The mean measu ed seasonal NEE o hummocks was highe han he NEE o lawns in e e y yea du ing 2010-2013, excep in 2012 (Figu e 4). Howe e , he di e ence be ween he NEE o hum- mocks and lawns was s a is ically signi ican only in 2010 (Table 1). Assuming ha he g owing season a Kauhane a o e he ou -yea s udy pe iod 2010-2013 is conside ed o las ca. se en mon hs o hummocks and ca. six mon hs o lawns, he seasonal ca bon balance was 310 g CO2-C m−2 o hummocks and 233 g CO2-C m−2 o lawns, espec i ely. The mean measu ed seasonal RE in he da k o hummocks du ing 2010-2013 was 723, 537, 402 and 566 mg CO2 m−2·h−1, espec i ely, and o lawns 417, 259, 282 and 270 mg CO2 m−2·h−1, espec i ely (Figu e 4). The mean measu ed seasonal RE o hummocks was clea ly highe han he RE o lawns in e e y yea du ing 2010-2013 (Figu e 4). The di e ence be ween he RE o hummocks and lawns was signi ican in e e y yea du ing 2010-2013 (Table 1). 4.Discussion In ou ou -yea s udy he in e -annual a iabili y in clima ic condi ions was conside able and pa ly unexpec ed as epo ed in o he mul i-yea s udies (e.g. [26]) as well. Fo ins ance, du ing he s udy pe iod he e was a e y wa m g owing season in 2010, bu a cold season in 2012 oo. Addi ionally, al hough he season o 2012 was he coldes du ing ou s udy pe iod 2010-2013, he snowmel was, howe e , he ea lies occu ing al eady in he middle o Ma ch. In gene al, ins an aneous NEE and RE in ou s udy oughly co esponded o hose measu ed in o he s udies on p is ine mi es [26]- [29]. Likewise o he abo e s udies, annual a ia ion in NEE and RE esul s was consid- e able in ou s udy, highligh ing he impo ance o mul i-yea empi ical s udies. The mean measu ed seasonal NEE, i.e. he ne ca bon seques a ion, o hummocks du ing 2010-2013 was gene ally sligh ly highe han he NEE o lawns, bu he di e ences be ween he NEE o mic o opog aphical habi a s we e a he small and no signi ican , excep in 2010. Howe e , he mean measu ed seasonal RE o hummocks was clea ly highe han he RE o lawns in e e y yea du ing 2010-2013, and he di e ence be ween he RE o hummocks and lawns was signi ican in e e y yea du ing 2010-2013. A eason o he mo e signi ican di e ences in RE han NEE, may be he highe sensi i i y o RE on al e a ions in WTL, in pa icula du ing ea ly sp ing and la e au umn when he di e ences in WTL be ween hummocks and lawns we e a g ea es . Also Riu a e al. [26] and Ballan yne e al. [30] epo ed he signi ican ly inc eased RE wi h lowe ed WTL on bo eal poo ens. The o he impo an eason o he obse ed highe seasonal ca bon seques a ion o hummocks han ha o lawns besides he sligh ly highe a e o ca bon accumula ion was he longe snow- and inunda ion- ee pe iod on hummocks, i.e. he du a ion o physiologically ac i e g owing season. The e is s ong e idence ha he in- e annual a ia ion o he ca bon seques a ion on bo eal mi es o igina es om he a ia ions in he snow- ee N.Sil an,K.Jokinen 109 Hummock 2010 CO2- lux mg m -2 h -1 -1000 -500 0 500 1000 1500 NEE RE Lawn 2010 Hummock 2011 -1000 -500 0 500 1000 1500 Lawn 2011 Hummock 2012 -1000 -500 0 500 1000 1500 Lawn 2012 Hummock 2013 Ap May Jun Jul Aug Sep Oc No -1500 -1000 -500 0 500 1000 1500 Lawn 2013 Ap May Jun Jul Aug Sep Oc No Figu e 4. Measu ed ins an aneous CO2 exchange (NEE and RE) o he mic o opog aphical habi a s (hummocks and lawns) du ing 2010-2013. Table 1. The signi icances (F- and hei p- alues) o di e ences be ween he NEE/RE o he hummocks and lawns (mic o- o m e ec ) du ing 2010-2013. Tes esul s we e conside ed signi ican when p < 0.05, and ma ked by he as e isk. Mic o o m e ec 2010 2011 2012 2013 NEE F = 5.24; p < 0.05* F = 0.42; p = 0.522 F = 1.88; p = 0.177 F = 1.70; p = 0.199 RE F = 9.91; p < 0.05* F = 18.28; p < 0.05* F = 10.62; p < 0.05* F = 38.39; p < 0.05* pe iod [18] o om he a ia ions in he inunda ion [21]. Ou s udy shows ha longe snow- ee pe iod due o ea ly snowmel enhances mo e he ca bon seques a ion o mic o opog aphically highe habi a s (hummocks) N.Sil an,K.Jokinen 110 han he su oundings (lawns). This is mainly because o snow co e and oo high WTL (inunda ion) o he e - ec i e ca bon seques a ion in ea ly sp ing on he mic o opog aphically lowe lawns. In ou s udy, he pho osyn hesis o mi e ege a ion did no occu unde snow co e o unde inunda ion, al- hough he pho osyn he ic ac i i y o bo eal dwa sh ubs unde snow co e has shown o ake place [31] [32]. A Kauhane a, he LAI o ascula plan s was e y low, and he majo pa o pho osyn he ic ac i i y was due o Sphagnum mosses ha a e no likely capable o pho osyn hesis unde snow. Howe e , Sphagnum mosses ha e he abili y o g ow unde lowe sola i adiance and empe a u e condi ions han he ascula plan s [19] [20]. Acco dingly, Sphagnum mosses g ow in low empe a u e condi ions immedia ely a e snowmel and/o a e he emo al o inunda ion in ea ly sp ing, o in low sola i adiance condi ions in la e au umn. Since he inc ease o g eenhouse gases in he a mosphe e is expec ed o ins iga e wa ming in high no he n la i udes especially du ing win e and ea ly sp ing [33]- [35], he snowmel will ake place ea lie in he u u e, and his will p obably p olong he e ec i e g owing season especially du ing ea ly sp ing in a he high sola i adiance condi ions [36] [37]. The abili y o plan s o bene i om in e mi en wa m pe iods du ing win e and ea ly sp ing, wi hou succumbing o eezing damage du ing subsequen pe iods o os , depends on a delica e balance be ween ac- i i y and p o ec ion, which may easily ip o e in condi ions whe e he annual win e - and sp ing ime empe a- u es a e ising [31] [32]. Plan s ha ing a capabili y o he e ec i e win e - and sp ing ime pho osyn hesis, like Sphagnum mosses, may signi ican ly bene i om inc eased win e ime empe a u es and ea lie snowmel . Sphagnum mosses a e known as a mi e plan g oup ha is he mos sensi i e o en i onmen al condi ions, es- pecially o soil mois u e, as a esul o an op imum WTL close o he su ace and na owes ole ance o WTL a ia ion [26] [38] [39]. Fu he mo e, un a o able en i onmen al condi ions may diminish di ec ly he amoun o phy omass, i.e. in e ms o he abundance and co e age, o a ce ain Sphagnum g oup [26]. Also ou s udy demons a ed ha mic o opog aphically sca e ed, unc ional plan g oups on a bog di e ed in hei esponses o snow co e and WTL and, consequen ly, changes in snow co e and WTL may modi y hei con ibu ion o he ecosys em CO2 dynamics in he u u e. In pa icula , he hummock- o ming Sphagnum mosses ha exposed i s ly om snow co e showed o gain addi ional ime o pho osyn hesis and hus u he bene i compa ed o o he mi e plan s. This may u he enhance he expansion o hummock- o ming Sphagnum moss domina ing he aised bogs owa ds no he n aapa-mi e egion due o he global wa ming. Since Sphagnum is one o he main pea o ming and ca bon accumula ing plan genus globally, he la ge-scale shi ing om lawn- o ming Sphagnum mosses owa ds hummock- o ming Sphagnum mosses in no he n bo eal egion may play a signi i- can ole in he global ca bon balance. 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