The effect of temperature on growth and competition between Sphagnum species

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1 Oeologi (28) 156: DOI 1.17/s ECOSYTEM ECOLOGY - ORIGINAL PAPER The effet of temperture on growth nd ompetition etween Sphgnum speies Angel Breeuwer Æ Monique M. P. D. Heijmns Æ Bjorn J. M. Roroek Æ Frnk Berendse Reeived: 4 Jnury 27 / Aepted: 7 Jnury 28 / Pulished online: 19 Ferury 28 Ó The Author(s) 28 Astrt Pet ogs ply lrge role in the glol sequestrtion of C, nd re often dominted y different Sphgnum speies. Therefore, it is ruil to understnd how Sphgnum vegettion in pet ogs will respond to glol wrming. We performed greenhouse experiment to study the effet of four temperture tretments (11.2, 14.7, 18. nd 21.4 C) on the growth of four Sphgnum speies: S. fusum nd S. ltium from site in northern Sweden nd S. mgellnium nd S. uspidtum from site in southern Sweden. In ddition, three omintions of these speies were mde to study the effet of temperture on ompetition. We found tht ll speies inresed their height inrement nd iomss prodution with n inrese in temperture, while ulk densities were lower t higher tempertures. The hollow speies S. uspidtum ws the lest responsive speies, wheres the hummok speies S. fusum inresed iomss prodution 13-fold from the lowest to the highest temperture tretment in monoultures. Nutrient onentrtions were higher t higher tempertures, espeilly N onentrtions of S. fusum nd S. ltium inresed ompred to field vlues. Competition etween S. uspidtum nd S. mgellnium ws not influened y temperture. The mixtures of S. ltium with S. fusum nd S. ltium with S. mgellnium showed tht S. ltium ws the stronger ompetitor, ut it lost ompetitive dvntge in the highest temperture Communited y Alln Green. A. Breeuwer (&) M. M. P. D. Heijmns B. J. M. Roroek F. Berendse Nture Conservtion nd Plnt Eology, Deprtment of Environmentl Sienes, Wgeningen University, P.O. Box 47, 67 AA Wgeningen, The Netherlnds e-mil:.reeuwer@gmil.om tretment. These findings suggest tht speies undnes will shift in response to glol wrming, prtiulrly t northern sites where hollow speies will lose ompetitive strength reltive to hummok speies nd southern speies. Keywords Bog Cover hnge Glol wrming Greenhouse Speies omposition Introdution Pet ogs ply lrge role in the glol sequestrtion of C. Although northern petlnds over only 2% of the totl lnd surfe, they store out one-third of the world soil C in the form of pet (Gorhm 1991). It is therefore importnt to know how omrotrophi og eosystems, whih form lrge prt of northern petlnds, will respond to predited limte hnges, espeilly sine the rise in temperture is expeted to e ove the glol verge t high ltitudes (Christensen et l. 27) where the mjority of pet ogs our (Kivinen nd Pkrinen 198; Gunnrsson 25). Vegettion in omrotrophi ogs is often dominted y different Sphgnum speies. The Sphgnum speies ount for the ulk of the C sequestrtion in pet euse of their relitrnt litter (Coulson nd Butterfield 1978; Clymo nd Hywrd 1982; Limpens et l. 23). Therefore, it is ruil to understnd how Sphgnum vegettion in ogs will respond to glol wrming in order to predit the role of ogs s C sinks in the future. Severl studies hve reveled differenes in prodution (Lindholm nd Vsnder 199; Gerdol 1995; Asd et l. 23; Gunnrsson 25) nd in deomposition rte (Rohefort et l. 199; Johnson nd Dmmn 1993; Belye 1996; Limpens nd Berendse 23) etween different Sphgnum speies. These differenes etween speies re often relted to

2 156 Oeologi (28) 156: differenes in mirohitt preferene (Gunnrsson 25). Within og, different Sphgnum speies our t different heights ove the wter tle nd t different positions long ph nd nutrient grdients (Andrus 1986; Sjörs nd Gunnrsson 22; Limpens et l. 23). The most ovious division in mirohitt preferene is etween hollow speies, whih grow in pools nd t shllow wter levels, nd hummok speies, whih grow t deeper wter levels. Hummok speies n lso grow t higher wter levels, ut they re then usully outgrown y hollow speies (Rydin 1986, 1993, 1997). However, the ompetitive ility of speies my differ etween yers, sesons nd lotions, nd s suh, ompetitive replement ours very slowly, if t ll. This results in reltively stle ompetitive lne etween speies (Rydin 1997). Severl studies found positive reltion etween Sphgnum produtivity nd temperture (Moore 1989; Sonesson et l. 22; Gunnrsson 25). The positive effet tht inresed temperture might hve on C sequestrtion in ogs is, however, often diminished y the positive effet of temperture on deomposition rtes (Hoie 1996). Inresed deomposition rtes lso led to inresed rtes of nutrient relese from the pet lyer, enhning prodution rtes even further. A hnge in temperture influenes not only the prodution nd deomposition of individul Sphgnum speies ut lso the ompetitive lne tht exists etween speies. An importnt hllenge fing eologists is to predit how limte hnge will lter speies distriutions in eosystems (Mooney 1991). Roroek et l. (27) lredy found different responses in iomss prodution mong speies when temperture ws inresed. It n e imgined tht when speies with high prodution nd/or low deomposition rte inreses its reltive undne in og, this will inrese the C storge pity of the system. Not only re there different ompeting speies within og, ut there re lso differenes in dominnt speies etween ogs when different limti regions re ompred. In this study, we used speies from two different sites. At the site in northern Sweden, Sphgnum ltium nd Sphgnum fusum re the dominnt speies while t the site in southern Sweden these speies lso our, ut Sphgnum mgellnium nd Sphgnum uspidtum re the most undnt speies. This orresponds with the generl distriution of these speies in Europe sine oth S. mgellnium nd S. uspidtum our further south thn S. fusum nd S. ltium (Dniels nd Eddy 1985). To exmine the effet of temperture on the ompetition etween speies, we performed greenhouse experiment in whih we studied the effet of four temperture tretments on the growth of the four speies: S. fusum nd S. ltium from northern Swedish site nd S. mgellnium nd S. uspidtum from southern Swedish site. Three omintions of speies were mde to study the effets of temperture on interspeifi ompetition. In our experiment we tried to nswer the following questions: 1. Wht is the effet of inresed temperture on the growth of different Sphgnum speies? We expet ll speies to show n inrese in oth height inrement nd iomss prodution s diret result of inresed temperture nd indiretly through inresed nutrient vilility. 2. Wht is the effet of temperture on ompetition etween speies? Sine S. fusum nd S. mgellnium grow in drier nd therefore lso wrmer mirohitts thn S. ltium nd S. uspidtum respetively, we expet these speies to e etter dpted to higher tempertures. S. mgellnium grows t more southern sites thn S. ltium, so we expet this speies to e etter dpted to higher tempertures. Consequently, we hypothesize tht inresed temperture will hve positive effet on ompetitive ilities of the hummok nd southern speies, leding to reltively lrger inrese in height inrement nd iomss prodution with temperture thn for hollow nd northern speies. Mterils nd methods Plnt mteril In August 24, Sphgnum ores (dimeter 16 m, height m) were olleted t two different sites in Sweden. From the northern site Lppmyrn (64 9 N, E), 3 Sphgnum fusum (Shimp) H. Klinggr ores nd 4 Sphgnum ltium (Russ.) C. Jens. ores were olleted. This site is string flrk mire or mixed mire with ridges of hummoks nd hollows where S. fusum is dominnt on the hummoks nd S. ltium in the dryer prts of the hollows. When identifying the speies from this site in the l, we found speimens of oth S. ltium nd Sphgnum ngustifolium (Russ.) C. Jens. These speies re diffiult to distinguish, whih oth Russow (Smith 1978) nd Klinggrff (Dniels nd Eddy 1985) reognized when they identified oth speies s vriets of Sphgnum reurvum. In our smples, we were unle to quntify the ext perentges of S. ltium nd S. ngustifolium. As result, whenever we mention S. ltium, we re referring to mixture of S ltium nd S. ngustifolium. From the southern site Sxnäs Mosse (56 51 N, E), 4 Sphgnum mgellnium (Brid.) ores nd 3 Sphgnum uspidtum (Hoffm.) ores were olleted. At this site S. mgellnium ours on the lwns nd low hummoks nd S. uspidtum in the hollows nd pools.

3 Oeologi (28) 156: Cores were tken from monospeifi stnds of eh Sphgnum speies ([95%) with sprse vsulr plnt over (\5%). The ores were pled in plsti ontiners (dimeter 16 m, height 22 m). Vsulr plnts were lipped flush with the Sphgnum, nd other Sphgnum speies were removed with tweezers. The ontiners were rought to Wgeningen nd stored outside for 8 weeks efore the greenhouse ws ville. As result, ontiners from oth sites ould limte to the sme limte to some extent. Experimentl design At the strt of the experiment, the ontiners were rought into the greenhouse nd rndomly divided over the tretments nd five replite loks, with seven speies omintions (four monoultures nd three mixtures) nd four temperture tretments per lok. All four speies were kept in monoulture nd the following three speies omintions were mde to study interspeifi ompetition: two northern speies S. fusum with S. ltium, two southern speies S. mgellnium with S. uspidtum nd northern with southern speies S. ltium with S. mgellnium. To study ompetition etween northern nd southern speies we hose the omintion of S. ltium nd S. mgellnium euse they our t similr wter levels. To mke the omintions, the ores were ut into four equl qurters nd two qurters of oth speies were pled lterntely in n empty ontiner. In potting the speies omintions, we mde ertin tht the surfe of the mixture ws uniform. We did not ut monoultures in four qurters, ut nother experiment showed no differene in wter ontent etween ut nd unut monoultures (Roroek et l. 27). The experiment ws onduted in four djent limte ontrolled greenhouse omprtments from Novemer 24 till April 25 for totl of 154 dys. Eh omprtment ws ssigned one of four temperture tretments. Tretments nd ontiners were swithed etween omprtments every 2 weeks to minimize ny effet of the different omprtments. The position of the loks nd the position of ontiners within the loks were lso swithed every 2 weeks. The verge dy tempertures in the four temperture tretments were 11.2, 14.7, 18. nd 21.4 C, respetively (Tle 1). During the drk period of 8 h, the dy temperture ws lowered y pproximtely 3 9.3, 11.6, 15.5 nd 18.9 C, resulting in men tempertures of 1.6, 13.7, 17.2 nd 2.6 C in temperture tretments 1, 2, 3 nd 4, respetively. In the region of the northern site, the men temperture in July is 14.7 C (Alexndersson et l. 1991) nd in the southern site the men temperture in July is 17. C (Mlmer et l. 23). A light period of 16 h ws pplied. If light intensity ws low during this period, SON- T AGRO 4 (Philips Powertone 4) lmps were used. Reltive humidity during the dy ws set t 75%. In the greenhouse it ws not possile to keep the reltive humidity extly the sme with ll tempertures. The rise in temperture etween tretments orresponded with derese in reltive humidity, whih used n dditionl inrese in vpour pressure defiit (VPD) with temperture (Tle 1). The differene in reltive humidity only explined 33% of the inrese in VPD with the highest temperture. If reltive humidity would hve een equl in ll omprtments, VPD would still hve een twie s high t temperture 4 s t temperture 1. Our highest VPD of.7 kp with temperture of 21.4 C is tully still quite low ompred to field onditions. Although not mny dt on VPD re pulished for similr eosystems, Hoie nd Chpin (1998) did find the following vlues for VPD in Toolik Lke, Alsk, in June nd July: in open field sites, kp with tempertures rnging from 5.9 to 22.5 C; nd under smll plsti greenhouses, kp with tempertures rnging from 6.4 to 31.1 C. Dorrepl et l. (23) mesured VPD of 1.54 under norml onditions nd 1.41 in open-top hmers with n verge temperture of 15 C in June nd July in Aisko, Sweden. The wter level ws set to 1 m elow pitul t the strt of the experiment. All speies were sujeted to the sme wter level, so tht temperture ws the only hnging environmentl vrile. This reltively high Tle 1 Dy nd night men vlues of temperture ( C), reltive humidity (%) nd vpour pressure defiit (VPD) (kp) of the four tretments, ±SE, n = 154 Tretment Temperture Reltive humidity VPD Dy Night Dy Night Dy Night T ±.4 93 ± ± ±.4.24 ±.1.16 ±.1 T ± ± ± ±.5.39 ±.1.25 ±.1 T3 18. ± ± ± ±.4.51 ±.1.42 ±.1 T ± ± ± ±.5.7 ±.1.59 ±.1

4 158 Oeologi (28) 156: wter level ws used for ll speies euse hollow speies nnot grow t low wter levels; while hummok speies n survive the environmentl onditions of hollows quite well; nonetheless, they re sent from these res euse of ioti ftors (Rydin nd MDonld 1985). Grosvernier et l. (1997) found tht growth in height nd dry weight is equl for S. fusum grown t wter levels of 1 m nd 4 m elow moss surfe while, for S. mgellnium nd espeilly for Sphgnum fllx, growth in height nd dry weight is muh greter with the high wter level. During the experiment n rtifiil rinwter solution, n 8,-fold dilution of se wter solution (Grrels nd Christ 1965), ws dded twie week to ring the wter level k to 1 m elow pitul. The mount of wter dded ws used s mesure of evportion. The drop in the wter tle ws highest in the highest temperture tretment, ut wter level never dropped more thn 6 m elow moss surfe etween two wter dditions. In numer of ontiners, Sphgnum grew higher thn 1 m ove the ontiner. To keep the wter level t 1 m elow the moss surfe, plsti ridge ws glued onto the ontiners nd the rk ws filled with silione kit. Wter ontent ws mesured using thet proe (Delt-T Devies, Cmridge, UK) efore the finl hrvest of the experiment. This ws done 3 4 dys fter wtering the ontiners for the lst time, so the wter ontent would reflet possile differenes etween tretments. Mesurements Height inrement of the Sphgnum rpet ws mesured non-destrutively every month using vrition of the rnked wire method (Clymo 197). We used plsti rods tht were inserted to depth of pproximtely 8 m nd nhored y plsti room ristles, this method kept the rnked wires firm t the sme ple so they did not move with Sphgnum growth. Two plsti rods were inserted in the monoultures nd one plsti rod ws inserted in eh qurter of the mixtures. The rods hd dimeter of 1.5 mm nd did not seem to interfere with the growth of the surrounding Sphgn. At the end of the experiment, olumns with dimeter of 5 m were ut round eh rnked wire nd ut off t 5 m length. Eh olumn ws put in plsti Ziplok g nd fresh weight ws determined. All gs were stored t 1 C till further mesurements ould e tken. Cpitul were defined s the top 1 m of eh individul plnt nd stem s the 1 4 m prt. Cpitul nd stems were seprted per olumn nd oven dried t 7 C for t lest 48 h nd then weighed. The weight of the totl smple ws used to lulte ulk density nd the iomss prodution per squred entimetre to ount for hnges in pitulum density. For nutrient nlyses, smples of pitul were pooled per speies for eh ontiner. Totl N, P nd K onentrtions were determined y digesting 3 mg of homogeneous, milled mteril with H 2 SO 4, sliyli id, Se nd H 2 O 2. All smples were nlysed for totl N nd P spetrophotometrilly using n uto-nlyzer (Sklr). K onentrtions were mesured with n tomi sorption spetrophotometer (Vrin AAS). To ompre pitulum ulk density nd nutrient onentrtions with field vlues, we olleted five smples (d = 5 m) from monoultures of the four Sphgnum speies in the two Swedish sites in August 26. Mesurements on pitulum ulk density nd nutrient onentrtions were exeuted s desried ove. To mesure the hnge in over of the speies in the mixtures, digitl pitures were mde t the strt nd t the end of the experiment. In these pitures we mesured the totl surfe over per speies in eh pot with Imge J (Armoff et l. 24). The iomss prodution per unit re (g m -2 ) ws lulted s follows: height inrement ðmþ finl ulk density totl smple ðg m 3 Þ ð%over end =%over strt Þ: Dt nlysis Dt were tested for normlity nd equlity of vrine. When neessry, dt were squre-root trnsformed to hieve homogeneous vrines. Blok effet ws tested s rndom ftor. When no lok effet ws deteted, whih ws usully the se, lok ws omitted from the nlysis to gin extr df. All nlyses were onduted using the SPSS sttistil pkge for Windows (12.). One ontiner with monoulture of S. ltium under temperture 4 ws hevily ffeted y fungl infetion, proly Lyophyllum plustre. After 4 months, 9% of the plnt mteril hd died. This ontiner ws further omitted from the nlyses. Height inrement in monoultures ws tested per speies with one-wy ANOVA with temperture s independent ftor. Height inrement, iomss prodution, over hnge, ulk density, wter ontent nd nutrient onentrtions were tested per speies. Two-wy ANOVAs were performed with temperture nd speies omintion s independent ftors. The effet of temperture, speies nd ompetition on the onentrtions of N, P nd K ws tested using three-wy ANOVA. Differenes etween the tretments were nlysed using Tukey post ho test. To test how the environmentl vriles temperture, N onentrtion nd wter ontent influened iomss prodution we performed stepwise regression nlysis per speies.

5 Oeologi (28) 156: Results Height inrement In the monoultures, the height inrement inresed with temperture in eh speies (Fig. 1, Tle 2). For S. uspidtum this effet ws lest distint with the lowest height growth t temperture 2 nd no differene in growth etween tempertures 1, 3 nd 4. Only S. fusum showed no differene in height inrement etween monoulture nd mixture. All other speies showed growth redution in mixtures (Tle 2). There were no signifint intertions etween the effet of temperture nd ompetition on height inrement, exept for S. ltium in omintion with S. mgellnium (Tle 2). Temperture inresed height inrement of S. ltium in monoulture, while there ws no effet of temperture in mixture with S. mgellnium (Figs. 1, 2 ). When we ompred height inrement etween the two speies in eh mixture, the wet speies S. ltium nd S. uspidtum hd higher vlues thn the dry speies S. fusum nd S. mgellnium t temperture tretments 1 nd 2 (Fig. 2). When temperture inresed, the differenes in height inrement etween the two speies disppered. Cover The hollow speies S. ltium nd S. uspidtum inresed in re in 53 out of 6 ontiners when growing in the mixtures. In the other seven ontiners (three with S. mgellnium + S. ltium, two with S. fusum + S. ltium, two with S. mgellnium + S. uspidtum), over hnged less thn 5%. For S. ltium there were signifint effets of temperture (F = 3.67, P =.23) nd neighouring speies (F = 4.95, P =.33) on expnsion (Fig. 3, ). Mximum hnge in over ws for S. ltium in omintion with S. fusum with temperture 2 nd 3. There ws no effet of temperture on expnsion of S. uspidtum (Fig. 3, F =.88, P =.47). Biomss prodution The response of iomss prodution to the temperture tretments ws similr to the response of height inrement (Tle 2). In ll speies iomss prodution inresed with inresed temperture. S. fusum showed the strongest response; this speies inresed its iomss prodution 13-fold from the lowest to the highest temperture tretment in monoultures (Fig. 4). Only for S. ltium in omintion with S. mgellnium ws there signifint intertion etween temperture nd speies omintion in iomss prodution (Tle 2). Temperture inresed iomss prodution of S. ltium in monoulture nd in mixture with S. fusum, while there ws no effet of temperture in mixture with S. mgellnium. When differenes in iomss prodution etween monoultures nd mixtures re ompred per temperture tretment, it shows tht S. fusum suffered from ompetition with S. ltium t temperture 3 euse prodution ws lower in mixture thn in monoulture, ut it no longer suffered t temperture 4 (Fig. 4). At temperture 4 S. ltium does suffer from ompetition with S. fusum, ut not t lower tempertures. In the mixtures of S. mgellnium nd S. ltium, S. mgellnium suffers from ompetition t temperture 1 nd 2, wheres S. ltium suffers from ompetition t temperture 3 nd 4 (Fig. 4). Biomss prodution of S. uspidtum did not show ny effet of ompetition with S. mgellnium, while iomss prodution of S. mgellnium did suffer from ompetition t tempertures 1, 2 nd 3 (Fig. 4). Fig. 1 Height inrement of speies in monoultures (m). Dt re men vlues ± SE, n = 5 exept for Sphgnum ltium t T4, n = 4. Different letters indite signifint differenes (P \.5) etween temperture tretments within eh speies. For temperture tretments, see Tle 1 Height inrement (m) ) S. fusum ) S. ltium ) S. mgellnium d) S. uspidtum Temperture tretment

6 16 Oeologi (28) 156: Tle 2 F-vlues nd P-vlues nd diretion of min effets influening height inrement nd iomss prodution per speies, orreted for over, using two-wy ANOVA Temperture Comintion T 9 omintion F P Effet F P Effet F P Height inrement Sphgnum fusum (+Sphgnum ltium) \ S. ltium (+S. fusum) \ S. ltium (+Sphgnum mgellnium) \ S. mgellnium (+S. ltium) \ S. mgellnium (+Sphgnum uspidtum) \ S. uspidtum (+ S. mgellnium) 1.8 \ \ Biomss prodution S. fusum (+S. ltium) 2.99 \ \ S. ltium (+S. fusum) \ S. ltium (+S. mgellnium) 9.68 \ S. mgellnium (+S. ltium) 17.5 \ \ S. mgellnium (+S. uspidtum) \ \ S. uspidtum (+ S. mgellnium) Numer of oservtions n = 4, exept for S. ltium n = 39 In the stepwise regression for iomss prodution of S. ltium, wter ontent ws seleted s the most explntory vrile (R 2 =.36, P \.1). For iomss prodution of S. fusum (R 2 =.52, P \.1), S. mgellnium (R 2 =.36, P \.1) nd S. uspidtum (R 2 =.12, P =.31), temperture ws seleted s the most explntory vrile. Bulk density Bulk densities were lower t higher tempertures for ll speies, exept for ulk density of the pitul nd stems of S. uspidtum (Tle 3). Compred to field vlues, pitulum ulk density of S. fusum nd S. ltium deresed with temperture, while pitulum ulk density of S. mgellnium nd S. uspidtum seemed to inrese t low tempertures. Bulk densities of oth pitul nd stems were lower in mixtures thn in monoultures of S. fusum nd S. ltium. Similrly, in S. uspidtum the ulk density of the pitul ws lower in mixtures thn in monoultures. There were no signifint intertions etween temperture nd speies omintion. Nutrient onentrtions The onentrtions of ll nutrients (N, P nd K) differed etween speies nd rose with inresing temperture. N onentrtion ws lso ffeted y the intertions of temperture y speies (F = 2.66, P =.7) nd speies y omintion (F = 3.73, P =.6). At tempertures 1 nd 2, N onentrtions were lower for S. fusum nd S. ltium thn for S. mgellnium nd S. uspidtum, s ws lso the se in field vlues. At temperture 3, only the N onentrtion of S. ltium ws lower thn tht of S. mgellnium. At temperture 4, N onentrtions of S. ltium were lower thn those of S. mgellnium nd S. fusum (Tle 4). Compred to field vlues, ll speies showed n inresed N onentrtion with temperture. P nd K onentrtions were ffeted y temperture (P onentrtion, F = 9.32, P \.1; K onentrtion, F = 82.77, P \.1) nd speies (P onentrtion, F = 3.5, P =.31; K onentrtion, F = 3.86, P =.11). P nd K onentrtions were higher t high temperture for ll speies (Tle 4). P-vlues deresed, ompred to field vlues, while K onentrtion inresed ompred to field vlues. Evportion nd wter ontent Wter ontent deresed with temperture tretment (Tle 5). Wter ontent ws lowest in S. ltium in mixture with S. fusum. Evportion inresed with temperture nd therefore with VPD for ll speies (Tle 5). Evportion in S. fusum in oth monoulture nd mixture ws lower thn in other speies.

7 Oeologi (28) 156: ) 6 S. fusum S. ltium 5 d d d d Fig. 2 Height inrement of the individul speies t eh temperture tretment (see Tle 1) within the three mixtures of speies: Sphgnum fusum + S. ltium, Sphgnum mgellnium + S. ltium nd S. mgellnium + Sphgnum uspidtum. Dt re men vlues ± SE, n = 5. Different letters indite signifint differenes etween tretments (P \.5) Height inrement (m) Height inrement (m) Height inrement (m) 4 d ) 6 S. mgellnium S. ltium ) 6 S. mgellnium S. uspidtum Temperture tretment Disussion Effet of temperture on growth As expeted, ll speies in monoulture inresed height inrement with temperture (Fig. 1). All speies lso showed looser growth form with higher tempertures, whih resulted in lower densities (Tle 3). Despite the lower ulk density t higher tempertures, iomss prodution still inresed with temperture for ll speies (Tle 2, Fig. 4). The response of height inrement to temperture ws out ftor 2 lrger thn the response of iomss prodution. Growth of Sphgnum ws proly inresed y higher rte of photosynthesis nd higher N vilility. Photosynthesis in Sphgnum hs een shown to inrese with temperture up to n optimum round 2 25 C (Skre nd Oehel 1981; Hrley et l. 1989). When temperture inresed, the nutrient onentrtions in Sphgnum were higher (Tle 4). Moreover, N nd K onentrtion inresed ompred to field vlues (Tle 4). As iomss prodution lso inresed, N nd K uptke must hve inresed onsiderly with inresing temperture. No nutrients were dded with the rinwter solution, so the higher vilility of nutrients must hve ome from Sphgnum itself nd the pet elow. Proly the lower Sphgnum prts in the ontiners deomposed fster when the temperture ws higher, mking more N nd K ville for growth. This temperture-indued stimultion of nutrient minerliztion is proly lrger thn it would e in field onditions s the pet soil in the ontiners is surrounded y wrm ir on every side, resulting in reltively high soil tempertures in our experiment. However, it n e expeted tht inresed temperture s result of limte hnge will lso enhne deomposition rtes in field situtions (Hoie 1996), therey inresing nutrient vilility for oth Sphgnum nd vsulr plnts. The lower N onentrtions of S. fusum nd S. ltium ompred with S. mgellnium nd S. uspidtum t tempertures 1 nd 2 re proly used y the different sites of origin. In the northern site, the N deposition is muh lower (pproximtely.2 g N m -2 yer -1 ) thn in the southern site (pproximtely.7 g N m -2 yer -1 ) where S. mgellnium nd S. uspidtum were olleted. In this experiment we provided ner optiml growing onditions for Sphgnum with high wter level nd high humidity, whih explins why the Sphgnum plnts ould grow with lower ulk density nd still keep their pitul

8 162 Oeologi (28) 156: Fig. 3 Cover hnge for hollow speies: S. ltium in omintion with S. fusum, S. ltium in omintion with S. mgellnium nd S. uspidtum in omintion with S. mgellnium. Dt re men vlues ± SE, n = 5. There were no signifint differenes etween tretments (P \.5). For temperture tretments, see Tle ) S. ltium with S. fusum moist. However, Sphgnum wter ontent still deresed with n inrese in temperture. In field onditions it would proly not hve een possile for the Sphgnum plnts to hnge their density so muh sine it would hve led to prolems in mintining the wter ontent of the pitul. The effet of temperture on height inrement might therefore lso hve een less. In few field studies, no positive or even negtive effets of temperture on prodution were found. However, in these experiments there were other ftors esides temperture tht ould hve hd negtive effet on iomss prodution, like drought stress (Hoie et l. 1999; Weltzin et l. 21; Gunnrsson et l. 24) nd higher vsulr plnt over, whih ould hve resulted in etioltion of the Sphgnum plnts nd redued iomss prodution euse of inresed shding (Gunnrsson et l. 24). In other studies lso positive effets of temperture on height growth nd prodution were found for different speies, in oth greenhouse (Roroek et l. 27) nd field experiments (Moore 1989; Gerdol 1995; Sonesson et l. 22; Dorrepl et l. 23). In ordne with our hypothesis, Asd et l. (23) suggested tht Sphgnum speies respond positively to inresed temperture nd tht hollow nd lwn speies re more sensitive to temperture thn hummok speies. This, however, does not orrespond with the low response of S. uspidtum to temperture in our experiment. Dorrepl et l. (23) lso found derese in ulk density with inresed temperture. Sine the response of height inrement nd ulk density to temperture were in opposite diretions, the dry mtter prodution of S. fusum did not show signifint inrese with temperture. Our reltively high height inrement nd low density of S. fusum ompred to the vlues of Dorrepl et l. (23) n proly e explined y the muh higher wter levels in our experiment. Dorrepl et l. (23) used wter levels of -2 to -4 m elow moss surfe during their mesurements. However, the Sphgnum densities we mesured (Tle 3) greed quite well with densities from other studies (Lindholm nd Vsnder 199; Moore et l. 1998; Asd et l. 23). From our results, we onlude tht the height inrement nd iomss prodution of ll Sphgnum speies in ogs n inrese with n inrese in temperture. However, the literture shows us tht, prtiulrly under field onditions, this potentil response my not e relized in instnes of Cover hnge (%) Cover hnge (%) Cover hnge (%) ) S. ltium with S. mgellnium ) S. uspidtum with S. mgellnium Temperture tretment

9 Oeologi (28) 156: Fig. 4 Biomss prodution orreted for hnge in over for speies in monoultures (mono) nd in mixtures (mix) for eh temperture tretment (see Tle 1) nd speies omintion: S. fusum (fus) + S. ltium (l), S. mgellnium (mg) + S. ltium nd S. mgellnium + S. uspidtum (us). Dt re men vlues ± SE, n = 4 5. Different letters indite signifint differenes etween tretments (P \.5) Biomss prodution (g m-2) Biomss prodution (g m-2) ) S. fusum + S. ltium 8 Temperture Temperture ) S. mgellnium + S. ltium Temperture 1 Temperture 2 ) S. mgellnium + S. uspidtum Temperture 1 Temperture 2 Biomss prodution (g m-2) Temperture 3 Temperture 3 Temperture 3 Biomss prodution (g m-2) Temperture 4 Temperture 4 Temperture 4 fus mono fus mix l mix l mono mg mono mg mix l mix l mono mg mono mg mix us mix us mono ompetition from vsulr plnts, drought stress or extreme temperture inreses. Effet of temperture on ompetition We hypothesized tht inresed temperture will hve positive effet on ompetitive ilities of S. fusum nd S. mgellnium. This hypothesis ws onfirmed in the ompetition with S. ltium, sine the height inrement nd iomss prodution of S. ltium t the highest temperture tretment were no longer lrger thn those of S. fusum nd S. mgellnium (Figs. 2, 4). However, S. ltium still inresed its over t the expense of S. fusum nd S. mgellnium in ll mixtures (Fig. 3, ). This ould e expeted s the wter level we used ws reltively high nd in the rnge of the nturl hitt of these speies. These results orrespond to the findings from field experiment of Rydin (1986), who found n expnsion of S. ltium t the expense of S. fusum t wter level of -1 m. At wter levels of -5 nd -1 m, he found smll expnsion of S. ltium, ut t wter level of -15 m S. fusum showed lrge expnsion. In greement with the hypothesis, the differene in height inrement nd iomss prodution etween S. fusum nd S. ltium disppered s temperture inresed (Figs. 2, 4). S. fusum kept inresing height inrement with temperture, ut S. ltium lredy rehed mximum height growth t temperture 2, whih is omprle to the summer temperture in the site of origin of these speies. Also, the expnsion in over eme lower for S. ltium t temperture 4 (Fig. 3). As result, the differene in iomss prodution etween S. fusum nd S. ltium slowly deresed with n inrese in

10 164 Oeologi (28) 156: Tle 3 Bulk density of pitul setion, stem setion nd totl smple. Dt re men vlues ± SE, pooled within temperture tretment (see Tle 1) nd within ompetition tretment. Different letters indite signifint differenes etween tretments within speies (P \.5). There were no signifint intertions etween temperture nd ompetition tretments. fus S. fusum, l S. ltium, mg S. mgellnium, us S. uspidtum Field vlue Temperture Comintion T1 T2 T3 T4 Mono fus l mg l mg us Bulk density pitul (mg m -3 ) S. fusum 38 ± 2 35 ± 2 37 ± 2 21 ± 1 17 ± 1 3 ± 2 25 ± 2 S. ltium 32 ± 1 26 ± 1 16 ± 1 14 ± 1 14 ± 1 2 ± 1 18 ± 2 15 ± 1 S. mgellnium 19 ± 1 21 ± 1 18 ± 1 13 ± 1 13 ± 1 17 ± 1 15 ± 1 17 ± 1 S. uspidtum 19 ± 1 23 ± 1 22 ± 2 19 ± 1 19 ± 1 23 ± 1 19 ± 1 Bulk density stems (mg m -3 ) S. fusum 18 ± 1 16 ± 1 15 ± 2 11 ± 2 17 ± 1 14 ± 1 S. ltium 15 ± 1 11 ± 1 8 ± 1 9 ± 1 13 ± 1 9 ± 1 11 ± 1 S. mgellnium 11 ± 1 9 ± 8 ± 1 7 ± 9 ± 1 9 ± 1 8 ± S. uspidtum 1 ± 1 1 ± 1 7 ± 1 7 ± 1 8 ± 1 9 ± 1 Bulk density totl smple (mg m -3 ) S. fusum 22 ± 1 21 ± 1 17 ± 1 13 ± 1 2 ± 1 16 ± 1 S. ltium 17 ± 1 12 ± 1 1 ± 1 1 ± 1 14 ± 1 11 ± 1 12 ± 1 S. mgellnium 13 ± 1 11 ± 9 ± 1 8 ± 11 ± 1 1 ± 1 1 ± S. uspidtum 12 ± 1 12 ± 1 ± 1 9 ± 11 ± 1 11 ± Vlues for mteril from the sites of origin (Field vlues, n = 5) re given for omprison. Numer of oservtions for eh speies for eh temperture tretment: S. fusum nd S. uspidtum, n = 1; S. ltium, n = 14 15; S. mgellnium, n = 15. Numer of oservtions for eh speies for eh omintion, n = 19 2 temperture until there ws no signifint differene t the highest temperture. Apprently, the hummok speies S. fusum is etter le to profit from high inrese in temperture thn S. ltium, even t reltively high wter levels. This is onfirmed y the stepwise regression nlysis whih shows tht iomss prodution of S. fusum is orrelted most to temperture, nd iomss prodution of S. ltium to wter ontent. As ould e expeted, S. fusum s hummok speies hs higher wter ontent thn S. ltium, lso t higher tempertures (Tle 5), nd therefore n profit more from inresed temperture, euse wter does not eome limiting for growth. S. fusum lso seems to e the etter ompetitor for nutrients. The N nd P onentrtions in S. fusum tended to e higher in the mixtures thn in the monoultures, wheres in S. ltium the opposite ws the se (Tle 4). Indeed, S. fusum is known for its high N uptke rte (Juhiinen et l. 1998). Our results show tht S. ltium loses ompetitive strength with inresing temperture. With slight inrese in temperture in northern ogs, S. ltium my remin the stronger ompetitor t high wter levels, ut t higher temperture inreses, S. fusum will gin ompetitive dvntge over S. ltium, lso euse inresed temperture my led to lower wter tles in ogs. Reent limte hnge simultion models predit n inrese of 2.5 C in summer temperture in northern Europe, with inresing preipittion in northern Sndinvi (Christensen et l. 27). This limited rise in temperture, lmost similr to the inrese from temperture 2 to 3, would not ffet ompetition etween S. ltium nd S. fusum very strongly. However, the effet of predited inrese in winter temperture of 5. C (Christensen et l. 27) ould shift the ompetitive lne etween S. ltium nd S. fusum further, euse inresed snow over nd spring temperture hve een shown to inrese S. fusum prodution (Dorrepl et l. 23). For S. mgellnium nd S. uspidtum, temperture 3 is omprle to the summer temperture in their site of origin. There ws no effet of temperture inrese from temperture 3 to 4 on iomss prodution nd reltive performne of the speies. This implies tht with the predited inrese in temperture of 2.5 C (Christensen et l. 27), the ompetitive lne etween S. mgellnium nd S. uspidtum will remin unhnged. The mixtures of S. ltium nd S. mgellnium show the lrgest differene in height inrement nd iomss prodution t temperture 2, whih is omprle to the summer temperture in the site of origin of S. ltium. Also the expnsion in over of S. ltium ws highest t this temperture. When temperture inreses, the differene in height growth nd iomss prodution eme smller nd then disppered in mixtures, wheres in monoultures the differene in iomss prodution etween speies remined. This implies tht S. ltium s

11 Oeologi (28) 156: Tle 4 N, P nd K onentrtion (mg g -1 ) of the pitul. Dt re men vlues ± SE, pooled within temperture tretment (see Tle 1) nd within ompetition tretment. Different letters indite signifint differenes etween tretments within speies (P \.5). There were no signifint intertions etween temperture nd ompetition tretments. For revitions, see Tle 3 Field vlue Temperture Comintion T1 T2 T3 T4 Mono fus l mg l mg us N (mg g -1 ) S. fusum 6.5 ± ± ± ± ± ± ±.5 S. ltium 5.3 ± ± ± ± ± ± ±.4 9. ±.3 S. mgellnium 11.1 ± ± ± ± ± ± ± ±.3 S. uspidtum 1. ± ± ± ± ± ± ±.4 P (mg g -1 ) S. fusum.39 ±.3.19 ±.7.3 ±.2.4 ±.3.41 ±.4.31 ±.4.34 ±.4 S. ltium.36 ±.3.13 ±.9.26 ±.4.29 ±.3.29 ±.2.32 ±.4.22 ±.5.19 ±.5 S. mgellnium.29 ±.1.1 ±.6.18 ±.4.27 ±.4.37 ±.8.26 ±.7.21 ±.5.21 ±.3 S. uspidtum.31 ±.3.1 ±.8.18 ±.4.23 ±.2.26 ±.4.24 ±.4.15 ±.4 K (mg g -1 ) S. fusum 54 ± ± ± ± ± ± ±.3 S. ltium 4.7 ± ± ± ± ± ± ± ±.3 S. mgellnium 2.2 ± ± ± ± ± ± ± ±.3 S. uspidtum 2.2 ± ±.3 5. ± ± ± ± ±.3 Field vlues (n = 5) re given for omprison. Numer of oservtions for eh speies for eh temperture tretment: S. fusum nd S. uspidtum, n = 1; S. ltium: n = 14 15; S. mgellnium, n = 15. Numer of oservtions for eh speies for eh omintion, n = 19 2

12 166 Oeologi (28) 156: Tle 5 Wter ontent (% volume) t 5 m depth nd evportion (mm dy -1 ) per temperture tretment (see Tle 1) nd per speies omintion. Dt re men vlues ± SE. Different letters indite signifint differenes etween tretments (P \.5). There were no signifint intertions etween temperture nd ompetition tretments Numer of oservtions for eh temperture tretment: for wter ontent, n = 5; for evportion, n = 35. Numer of oservtions for eh ompetition tretment: for wter ontent nd for evportion, n =2 Wter ontent Evportion Temperture 1 88 ± ± ± ± ± ± ± ±.5 d Monoultures S. fusum 83 ± 5 S. fusum 1.3 ±.5 S. ltium 66 ± 6 S. ltium 1.7 ±.8 S. mgellnium 74 ± 4 S. mgellnium 1.8 ±.8 S. uspidtum 78 ± 4 S. uspidtum 1.8 ±.8 Mixtures S. fusum 74 ± 5 S. fusum + S. ltium 1.5 ±.7 S. ltium 49 ± 5 S. mgellnium 69 ± 5 S. mgellnium + S. ltium 1.6 ±.7 S. ltium 68 ± 5 S. mgellnium 82 ± 5 S. mgellnium + S. uspidtum 1.7 ±.8 S. uspidtum 73 ± 5 northern speies n enhne its prodution with n inrese in temperture s long s it grows in monoultures. If S. mgellnium expnded its distriution further to the north s result of glol wrming, it would e strong ompetitor for S. ltium, therey reduing S. ltium prodution. Gunnrsson et l. (24) lso showed tht S. ltium performs less well under ompetition with inresed tempertures. They performed ompetition experiment in poor fen, lose to the site of origin of the S. ltium mteril. They found tht when Sphgnum ppillosum ws trnsplnted to n re with S. ltium, S. ppillosum deresed in re y 3%. However, when temperture ws inresed y 3.6 C, S. ppillosum inresed y 42%. This tretment is omprle to the inrese from temperture 2 to temperture 3 in our experiment ut with lower wter tles, rnging from 5 to 17 m under the moss surfe. Generlly, we onlude from our experiment tht n inrese in temperture n fvour hummok nd lwn speies ompred to hollow speies. This orresponds to the findings of Muquoy et l. (22), who showed from pet ore nlyses tht in periods with lower temperture, due to deresed solr tivity, there ws shift in representtion from lwn nd hummok speies to hollow speies in omrotrophi mires in Denmrk nd the UK. In onlusion, our findings suggest tht prodution rtes n inrese nd tht Sphgnum speies undnes n shift in response to glol wrming, prtiulrly t northern sites. There, hollow speies suh s S. ltium will lose ompetitive strength reltive to hummok speies suh s S. fusum nd southern speies suh s S. mgellnium. Wht the onsequenes for the C lne of og eosystems will e depends not only on the prodution rtes, ut lso on deomposition. In generl, deomposition rtes lso inrese with temperture nd inresed N vilility (Hoie 1996; Limpens nd Berendse 23) nd hummok speies deompose slower thn hollow speies (Rohefort et l. 199; Johnson nd Dmmn 1993; Limpens nd Berendse 23), ut virtully nothing is known out the temperture sensitivity of deomposition of og plnt speies. Aknowledgments We thnk Murits Gleihmn nd Frns Möller for their prtil ssistne in the greenhouse nd with seprting nd weighing ll the smples, nd we thnk Jn vn Wlsem for the hemil nlysis. We lso thnk Urn Gunnrsson nd two nonymous reviewers for their onstrutive omments on this mnusript. This study ws finned y the Netherlnds Orgniztion for Sientifi Reserh (NWO-projet ). The experiments presented in this pper omply with the urrent lws of the Netherlnds. Open Aess This rtile is distriuted under the terms of the Cretive Commons Attriution Nonommeril Liense whih permits ny nonommeril use, distriution, nd reprodution in ny medium, provided the originl uthor(s) nd soure re redited. Referenes Armoff MD, Mgelhes PJ, Rm SJ (24) Imge proessing with imgej. Biophotonis Int 11:36 42 Alexndersson H, Krlström C, Lrsson-MCnn S (1991) Temperture nd preipittion in Sweden Referene normls. Swedish Meterologil nd Hydrologil Institute (SMHI), Meterologi, Norrköping Andrus RE (1986) Some spets of Sphgnum eology. Cn J Bot 64:

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