jo u r n al homep ag e: www.elsev ier .com/ locate /apsoi l
orthern peatland Collembola communities unaffected by threeummers of simulated extreme precipitation
veline J. Kraba,∗, Rien Aertsa, Matty P. Bergb, Jurgen van Hala, Frida Keuperc
Institute of Ecological Science, Department of Systems Ecology, Faculty of Earth and Life Sciences, VU University Amsterdam, De Boelelaan 1087,081 HV Amsterdam, The NetherlandsInstitute of Ecological Science, Department of Animal Ecology, Faculty of Earth and Life Sciences, VU University Amsterdam, De Boelelaan 1085,081 HV Amsterdam, The NetherlandsClimate Impacts Research Centre, Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden
r t i c l e i n f o
rticle history:eceived 3 December 2013eceived in revised form 6 March 2014ccepted 8 March 2014vailable online 5 April 2014
eywords:xtreme eventsrecipitationoil faunaeat bogunctional traitsommunity weighted mean
a b s t r a c t
Extreme climate events are observed and predicted to increase in frequency and duration in high-latitudeecosystems as a result of global climate change. This includes extreme precipitation events, which maydirectly impact on belowground food webs and ecosystem functioning by their physical impacts and byaltering local soil moisture conditions.
We assessed responses of the Collembola community in a northern Sphagnum fuscum-dominatedombrotrophic peatland to three years of experimentally increased occurrence of extreme precipitationevents. Annual summer precipitation was doubled (an increase of 200 mm) by 16 simulated extremerain events within the three months growing season, where on each occasion 12.5 mm of rain was addedwithin a few minutes. Despite this high frequency and intensity of the rain events, no shifts in Collemboladensity, relative species abundances and community weighted means of three relevant traits (moisturepreference, vertical distribution and body size) were observed. This strongly suggests that the peatlandCollembola community is unaffected by the physical impacts of extreme precipitation and the short-termvariability in moisture conditions. The lack of response is most likely reinforced by the fact that extremeprecipitation events do not seem to alter longer-term soil moisture conditions in the peat layers inhabited
by soil fauna.
This study adds evidence to the observation that the biotic components of northern ombrotrophicpeatlands are hardly responsive to an increase in extreme summer precipitation events. Given the impor-tance of these ecosystems for the global C balance, these findings significantly contribute to the currentknowledge of the ecological impact of future climate scenarios.
One-third of the world’s terrestrial carbon (C) is stored in high-atitude peatland soils (Gorham, 1991). As climate changes, theurnover of this C through decomposition and thereby the releasef C through soil respiration to the atmosphere, are expected toncrease significantly with potential feedbacks to climate (Gorham,991; Limpens et al., 2008; Dorrepaal et al., 2009). Not onlyhanges in average annual temperature and precipitation will affect
hese northern ecosystems, the increase in frequency and dura-ion of extreme climate events will have a potentially even largermpact (Alexander et al., 2006; Callaghan et al., 2010; Hansen
et al., 2012). Relatively short periods of heat spells, drought orhigh precipitation events can lead to changes in species’ physio-logical performance, relative abundances or even local-to-regionalextinctions and altered distribution patterns (Easterling et al.,2000; Smith, 2011; Bokhorst et al., 2012). Extreme precipitationevents are generally recognized as important drivers of ecosystemresponses to climate change in (sub)arctic ecosystems (Callaghanet al., 2010). Not only changes in the duration and amount of snowcover in winter (Dorrepaal et al., 2004; Bombonato and Gerdol,2012) but also alterations of summer rainfall patterns might havea significant impact on these ecosystems. Alterations in summerprecipitation regimes include long-term changes in precipitation
amounts, increased intensification of its variability and/or strongermagnitude of precipitation events. Such changes can alter local soilmoisture conditions but also impact on ecosystems by exertingphysical disturbance and introducing larger temporal variation in
oil moisture conditions (Beier et al., 2012). The extent of its impactsill for a large part depend on the ability of the soil to buffer precip-
tation effects and the ability of the plant and soil biota to acclimater adapt to the new conditions (Parmesan et al., 2000).
A relatively small number of studies investigated effects ofxperimentally increased summer precipitation on (sub)arcticcosystems (Karlsson, 1985; McGraw, 1985; Henry et al., 1986;arsons et al., 1994; Shevtsova et al., 1997; Press et al., 1998;obinson et al., 1998; Phoenix et al., 2001) and even fewertudies investigate specifically the effects on peatland vegetationSonesson et al., 2002; Keuper et al., 2012) and on its belowgroundood web (Krab et al., 2013; Tsyganov et al., 2013). Moreover, the
echanisms that cause potential effects on peatland biotic compo-ents of soils remain largely unclear. On the one hand, precipitation
nduced alterations in local soil moisture conditions can have a sig-ificant effect as soil moisture is an important driver of above-nd belowground processes and their linkages (Fisk et al., 1998).urthermore, a large part of the soils’ biota is dependent on localoisture conditions, since it inhabits the water filled pore space
Wallwork, 1970; Anderson, 2011). On the other hand, below-round responses to extreme rainfall events will not only be causedy potential alterations in substrate moisture conditions but alsoy other extreme rainfall-related factors, such as water perco-
ation, variation in short-term soil moisture conditions and thehysical impact of rain showers, which by its force can alter soiltructure, or directly disturb the soil biota living in shallower soilayers (Schönborn, 1977; Hodkinson et al., 1999; Shein et al., 2002;syganov et al., 2013).
Collembola are a keystone group of decomposers in the below-round food web of arctic ecosystems (Woodin and Marquis, 1997)nd are known to be particularly sensitive to fluctuations in soiloisture conditions (Huhta and Hanninen, 2001; Lindberg et al.,
002; Kærsgaard et al., 2004). Although they only modestly con-ribute directly to C turnover, their control over the biomass andctivity of microbial decomposers (Lavelle, 1997; Hättenschwilernd Gasser, 2005) can have a large impact on nitrogen (N) and Cynamics (Berg et al., 2001; Osler and Sommerkorn, 2007). Changes
n Collembola density, their spatial patterning or shifts in species orommunity trait composition might affect the activity of the micro-ial community (Crowther and A’Bear, 2012) and thereby impactignificantly on decomposition rates, and thus C turnover (Filser,002).
Assessing a community’s response to environmental drivers byeans of functional traits instead of the traditional taxonomic
pproach is currently considered to be an essential step in findingatterns in community responses and the mechanisms underlyinghem (McGill et al., 2006; Violle et al., 2007). This trait approachas developed initially to assess the response of different vegeta-
ion types to several environmental factors, but has recently alsoeen successfully used to explain species-specific responses of sub-rctic Collembola communities to climate change (Makkonen et al.,011; Bokhorst et al., 2012; Krab et al., 2013). For example, surface-welling peatland Collembola species were found more vulnerableo a single short-term extreme climate-warming event than deeperoil-dwelling species (Krab et al., 2013). In the same study Krabt al. (2013) have shown that a single short-term (17 days) extremencreased precipitation event did not have a significant short-termmpact on a Collembola peatland community. However, this short-erm experiment did not necessarily allow for conclusions aboutmpacts on reproduction or other longer-term effects. Longer-termncreases in extreme precipitation events could affect survival andeproduction success and thus Collembola density and community
tructure. Hence, a next critical step in researching the effects oflimate extreme events on Collembola communities in northerneatlands is to study its resilience to longer-term multiple sequen-ial extreme precipitation events.
ology 79 (2014) 70–76 71
Thereto, we subjected a dry subarctic Sphagnum fuscum-dominated bog to experimental doubling of the total ambientsummer precipitation. We increased the magnitude, the frequency(16 additional extreme rain events) and the intensity of precipi-tation events for three consecutive years. We assessed the impactof these regimes on Collembola density and relative species abun-dance, and calculated Community Weighted Means (CWMs) (Lepset al., 2006) of three relevant traits (moisture preference, verticaldistribution and body size), to reveal potential directional shiftsand to extrapolate consequences of species shifts for the func-tioning of the community. We hypothesized that an increase inthe magnitude, the intensity and the frequency of precipitationevents will have a significant negative effect on Collembola den-sities. Apart from a direct negative impact of the physical aspectsof extreme rainfall (‘flushing’, cf. Tsyganov et al., 2013) on Collem-bola densities, we also expect the increased frequency of theseevents to limit the recovery of the community. Further, we expectCollembola species to respond differently to the extreme events,resulting in shifts in relative species abundances. Specifically, theincreased magnitude of precipitation will potentially favour morehygrophilous species over xeric species. In addition, we expect therelative abundance of surface-dwelling species to decline, sincethese species will be more exposed to the physical impact of pre-cipitation events than deeper soil-dwelling species. In line withthis, average body sizes in the community will potentially changetowards smaller species, as deeper living soil-dwelling species aregenerally smaller and more hygrophilous than surface-dwellingspecies.
2. Methods
2.1. Site description
The experiment was conducted in the Stordalen nature reservein northern Sweden (68◦21′ N, 19◦03′ E, 351 m.a.s.l). This reservehas been described extensively by Sonesson (1980) and morerecently by Malmer et al. (2005). Annual precipitation in the areais around 300 mm year−1 (1913–2006) (Johansson et al., 2006).Summer precipitation at the site in the years of the experi-ment (2007–2009) was 287, 228 and 190 mm, respectively; witha mean of 235 ± 49 SD (Olefeldt and Roulet, 2012). Mean sum-mer temperature is 7 ◦C and mean winter temperature −6 ◦C. Theexperiment was set up on a dry elevated ombrotrophic Sphagnumfuscum (Schimp.)-dominated peatland (Rydén, 1976; Sonesson,1980) with an active layer thickness of about 50 cm. The vas-cular plant community consists of the evergreen dwarf shrubsEmpetrum hermaphroditum L. (56% of total aboveground biomass)and Andromeda polifolia L. (9%), the deciduous dwarf shrubs Betulanana L. subsp. nana (6%) and Vaccinium uliginosum (7%), the forbRubus chamaemorus L. (15%), and the graminoid Eriophorum vagi-natum L. (8%).
2.2. Experimental design
In the beginning of the summer of 2007, 16 visually simi-lar plots of 1 m2 were established in a random organization andfollowing a completely randomized design subjected to either pre-cipitation increase or an ambient treatment (n = 8). The plots wereseparated at least 2 m apart. The plots which received the precipita-tion treatment were evenly watered 16 times during the growingseason (June–August) and received 12.5 mm extra water (12.5 l)
at each watering occasion, using a watering can, with an inten-sity of approximately 3 mm min−1. This resulted in 200 mm extraprecipitation per growing season. Water for additional precipita-tion was taken from the stream adjacent to the experimental site
7 Soil Ecology 79 (2014) 70–76
aoosocttii(tudmSpuac
2
1d(Tlna7g72
2
tMCttaapvBt
esCTpsdwtapwd
Fig. 1. Soil moisture conditions of 8 control plots (light grey markers) and 8 precipi-tation increase plots (dark grey markers) at time of harvest. Markers are averages of
2 E.J. Krab et al. / Applied
nd had a conductivity of 50 ± 12 �S cm−1, pH 6.7 ± 0.2, dissolvedrganic carbon content of (DOC) 11 ± 3 mg l−1, and total nitrogenf (TN) 0.3 ± 0.2 mg l−1 (data based on measurements from twoeparate spots in the stream from the end of April until the endf September 2008) (Olefeldt and Roulet, 2012). Given the low Noncentration in the stream water and the low N deposition inhis subarctic region (Bergstrom et al., 2005) nutrient addition dueo using stream water does not seem to have been a confound-ng factor in our set-up. As a similar water addition experimentn a nearby S. fuscum peat bog did not affect soil temperaturesKrab et al., 2013) we assumed effects of water addition on soilemperatures to be minimal. The experiment lasted three consec-tive growing seasons (2007–2009). Soil moisture was measureduring the last summer of treatment both gravimetrically and byeans of moisture sensors (EC-5 Soil Moisture Smart Sensor e S-
MC-M005) inserted vertically in the top 5 cm of the S. fuscumeat and measuring every hour. Soil moisture is expressed in vol-metric soil moisture (cm3 H2O per cm3 core). S. fuscum corest carrying capacity contain approximately 0.7 cm3 H2O per cm3
ore.
.3. Harvest
In August 2009, from each plot, three soil cores (diameter2 cm, depth 8 cm) were taken with a soil corer from Sphagnum-ominated patches. This resulted in eight treatment replicateswater addition and ambient) and three within plot replicates.hese cores were packed water- and airtight, transported to theaboratory, weighted (to the nearest g) and placed in a Tullgren Fun-el fauna extractor (Van Straalen and Rijninks, 1982) within 24 hfter harvest. After soil fauna extraction cores were dried for 48 h at0 ◦C and dry weights of the S. fuscum cores were determined, forravimetric soil moisture measurements. Soil fauna were stored in0% ethanol, identified using Fjellberg’s identification keys (1998,007) and counted.
.4. Calculation and statistics
To assess the effect of increased precipitation on soil moisture atime of harvest, on Collembola density and Community Weighted
eans (CWMs) trait values we used one-way ANOVAs. To test ifollembola community composition was affected by water addi-ion (and thus for dissimilarities between communities found inhe control cores versus the water addition cores) we performed
permutation test for multifactorial multivariate analysis of vari-nce (One-way PERMANOVA, distance matrix: Bray–Curtis, no. ofermutations: 999) (Anderson, 2001). The test statistic is a multi-ariate analogue to Fishers F-ratio and is calculated directly from aray–Curtis similarity matrix (Bray and Curtis, 1957) P values arehen obtained using permutations.
To assess the impact of experimental extreme precipitationvents on Collembola density while taking into account localoil moisture conditions we conducted a One-way Analysis ofovariance (ANCOVA) (factor: treatment, covariate: soil moisture).his analysis was carried out on all replicates (including within-lot replicates) since within-plot soil moisture conditions differedubstantially and Collembola abundance and soil moisture wereetermined for each individual core (data not shown). In additione tested if Collembola density could be explained from soil mois-
ure conditions by a quadratic model by carrying out a regression
nalysis on soil moisture versus Collembola density (averaged perlot). All statistical analyses (except the regression analysis, whichas carried out using SPSS 19.0) were performed on untransformedata using R (version 2.15.3).
3 within-plot replicates. Volumetric soil moisture (cm3 H2O cm−3) was determinedgravimetrically from the cores that were taken for microarthropod extraction. Errorbars are standard deviations (n = 3).
We followed Garnier et al. (2004) and Leps et al. (2006) to cal-culate the CWMs for a whole community as:
CWM =n∑
k=1
Ak × FTk
where n is the number of species sampled in the community, Akis the relative abundance of species k in the community, and FTkis the functional trait of interest of species k in the community.The selected traits were: moisture preference, vertical stratificationpreference and maximum body size. For each trait we calculatedCWMs for each of the communities undergoing the precipitationtreatment and the control. The trait values of each species wereobtained from literature (maximum body size: Fjellberg, 1998,2007; moisture preference and vertical stratification: Kuznetsova,2003). Collembola species’ moisture preference and vertical strat-ification were assessed by subdividing them into six and threeclasses, respectively (Table 1). When moisture preference or verti-cal stratification class for species were not available from literaturewe estimated the class from Krab et al. (2013) or used data for aclosely related species of the same genus (Table 1).
3. Results
3.1. Soil moisture
Our extreme precipitation treatments did not alter averagelonger-term soil moisture conditions in the top 8 cm peat layer. Attime of harvest there was no significant effect of the water additiontreatment on soil moisture conditions when measured gravimet-rically (Fig. 1, Table 2). Within plot variation in soil moistureconditions was relatively high (Fig. 1). Experimental water additioncaused temporarily increased soil moisture conditions that gener-ally returned to pre-addition conditions within a day. However,these short-term higher soil moisture conditions fell within thevariation in local soil moisture conditions between different plots(Fig. 1, S1).
3.2. Collembola density community composition
A three-summer long increase in extreme precipitation eventsdid not affect total Collembola density (Fig. 2, Table 2), and varia-tion in local soil moisture conditions was not significantly related toCollembola density either (Table 2). A regression analysis showed
Table 1Collembola species list and their assigned species trait values/classes. Moisture preference classes according to Kuznetsova (2003): 1 = xero-resistant, 2 = xero-mesophilous,3 = proper mesophilous/no preference, 4 = meso-hygrophilous, 5 = hygro-mesophilous, 6 = proper hygrophilous. Vertical distribution classes according to Kuznetsova (2003)1 = euedaphic, 2 = hemi-edaphic, 3 = epigeic. Maximum body size (mm length) according to Fjellberg (1998, 2007).
Species Moisture preference (class) Vertical dist. (class) Body size (mm)
a Estimated vertical distribution/moisture preference from Krab et al. (2013) or by clos
Fig. 2. Stacked bar plot for Collembola densities of the 8 most dominant speciesie
tt
ttt
that an increase in precipitation magnitude would not necessarily
TS
n the control (C) and the precipitation increase (W) plots. Error bars are standardrrors for the total community density (n = 8).
hat neither a linear, nor a quadratic model could explain the dis-ribution of the data (Table 2).
Although there seemed to be a slight increase in the rela-
ive abundance of Friesea truncata, species distributions for bothhe control and the water addition plots were very similar atime of harvest (Fig. 2). The PERMANOVA analysis showed that
able 2ummary of results of the conducted statistical analyses.
Tested effect of treatment Test
Water volume at harvest One-way ANOVA
Collembola density One-way ANOVA
Collembola density and soil moisture One-way ANCOVATreatment
Soil moisture
Linear regression
Quadratic regression
Community composition Collembola One-way PERMANOVA
CWM vertical distribution One-way ANOVA
CWM moisture preference One-way ANOVA
CWM max body size One-way ANOVA
2a 1.6
ely related species from the same genus.
community composition did not significantly change due to anincrease in extreme precipitation events (Table 2).
3.3. Community weighted means
In line with the lack of Collembola community response, theexperimentally increased magnitude, intensity and frequency ofprecipitation events did not alter CWMs for the traits moisturepreference, vertical distribution and maximum body size (Fig. 3,Table 2).
4. Discussion
4.1. Precipitation manipulation did not alter soil moistureconditions
Despite the fact that our treatment doubled the amount of sum-mer precipitation, it did not significantly affect average bulk soilmoisture conditions in Collembola-inhabited layers of a S. fuscumpeatland. Although precipitation studies are known to have theirlimitations because of for example edge effects (Beier et al., 2012)we consider the lack in soil moisture increase in these layers aproper reflection of the hydrological properties of ombrotrophicpeatlands rather than an artefact of our precipitation treatment. Inombrotrophic peatlands lateral water runoff in the top 20–30 cm isvery limited due to the large pore size and the vertical orientation ofthe pores. In addition, water percolation is known to be fast throughthe 0–20 cm layer of these peat soils (Sonesson, 1980). This suggests
lead to longer-term changes in soil moisture conditions in the lay-ers in which soil fauna are active. In accordance with this, earlierresearch in a nearby S. fuscum dominated ombrotrophic peatland
Fig. 3. Community weighted mean trait values (CWM) for Collembola communitiesin the control (C) and precipitation increase (W) plots. The traits for which CWMs arecalculated are: (a) moisture preference, (b) vertical distribution and (c) maximumbody size. For moisture preference a higher value indicates a more hygrophilouscsE
spt8twof
4
dtccc
ommunity, and for vertical distribution preference a higher value represents a moreurface-dwelling species in the community. Maximum body size is expressed in mm.rror bars are standard errors (n = 8).
howed that a short-term (one summer) very extreme increase inrecipitation (382.5 mm spread over 51 rain events in 17 consecu-ive days) did only slightly change moisture conditions in the top
cm of the peat profile (Krab et al., 2013). This again emphasizeshat these peatlands are characterized by very rapid percolation ofater upon large and very intensive rainfall events. Which in its
wn term might have a considerable impact on the belowgroundood web.
.2. No effects on Collembola community structure
The Collembola community did not show a response in terms ofensity or species composition to the imposed extreme precipita-
ion treatment. This strongly suggests that the peatland Collembolaommunity is unaffected by the physical impacts of extreme pre-ipitation and the short-term variability in moisture conditions. Inontrast to our results, Tsyganov et al. (2013) showed that our water
ology 79 (2014) 70–76
addition treatment induced ‘flushing’ of Protozoan testate amoebaefrom the top peat layers. Likewise, Judd and Kling (2002) showedthat increased storm events reduced dissolved organic C concen-trations in tussock tundra by flushing. Extreme precipitation eventscould thus have had similar effects, or indirectly affect Collembolacommunities by flushing away nutrients or food sources, such asfor example Protozoa (Crotty et al., 2012), even without chang-ing longer term soil moisture conditions. However, we did notobserve a ‘flushing effect’ on the Collembola community. This canbe explained by the fact that Collembola might already endure sim-ilar ‘flushing’ yearly in spring, when snowmelt rapidly releases aconsiderable amount of water into the peat soils. Local heterogene-ity of soil moisture conditions due to the local topography may havemore impact on soil fauna community structure. We tested thispossibility, but we did not detect a straightforward link betweenthe soil moisture conditions of the cores measured at harvest andCollembola densities or community structure within those cores(Table 2).
We suspect that generally dryer systems or systems with otherhydrological properties tend to show a more positive effect of pre-cipitation increases on the soil fauna community by its effects onlong-term soil moisture conditions, since these ecosystems mightbe water limited, whereas in wetter systems that are already water-saturated these positive results would be absent. Indeed, in dryerecosystems Collembola generally seem to benefit from increasedprecipitation, however, a simultaneous increase in drought exhib-ited a significantly larger impact on the soil fauna community thanincreased precipitation (Frampton et al., 2000; Lindberg et al., 2002;Tsiafouli et al., 2005; Lensing and Wise, 2007).
In nearly water-saturated systems such as wet Sphagnum miresan increase in extreme precipitation events could potentially causeoxygen deficiency and a physical disturbance of the surface layers.These factors are more likely to negatively than positively affectthe Collembola community, as Collembola would be on the right(declining) side of their optimum curve in terms of their com-munity response to increasing soil moisture conditions. However,in this relatively dry S. fuscum-dominated peatland (Rydén, 1976;Sonesson, 1980) we did not observe a decline in density (Fig. 1).In accordance with this observation, a simulated short-term (17days) extreme rain event in a comparable subarctic S. fuscum peat-land showed no response of the Collembola community in terms ofabundance and diversity (Krab et al., 2013).
4.3. Collembola responses to microclimate related to speciesfunctional traits
Collembola are known to be sensitive to fluctuations in soilmoisture conditions (Huhta and Hanninen, 2001). Moreover, thesensitivity to (changes) in microclimatic conditions seems to bespecies specific and to largely depend on morphological traits(Krab et al., 2010). In this study, however, different species didnot respond differently to the extreme rain events and no shiftsin relative species abundances were observed. Specifically, we didnot observe our expected decrease in surface-dwelling species.Our results therefore do not support the hypothesis that surfaceliving species would be more exposed to the physical impact ofthe precipitation events than deeper soil-dwelling species. Fur-ther, the increased magnitude of precipitation did not favour morehygrophilous species over xeric species. Xeric species that gener-ally occupy the more shallow soil layers (Kuznetsova, 2003), wererather insensitive to the fluctuations in soil moisture conditions
than the extreme events have caused, and soil moisture conditionsin the deeper layers did not change to profit hygrophilous species.In line with this, average body size in the community did not changetowards generally smaller species, although soil-dwelling species
Soil Ec
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E.J. Krab et al. / Applied
re generally smaller and more hygrophilous than surface-dwellingpecies.
Certainly, other traits than the traits we selected could be moreesponsive to increased extreme precipitation events. Furthermore,
potential shift in trait distribution over the community rather thanhifts in CWMs (Mason et al., 2005) could have occurred. However,s the changes in relative species abundances were very minor,t would most likely not result in a CWM shift in non-accountedrait values or in unaccounted shifts in functional trait distributionver the community. If our Collembola community responded tohe increased precipitation events, it would most likely to be by traitlasticity (Berg and Ellers, 2010) which in particular in the contextf acclimation and adaptation to climatic changes might be highlyelevant. Unfortunately, our CWM analyses would not have pickedp such changes since the values for vertical distribution, moisturereference and maximum body, size were taken from literature andxed.
Although we did not observe a directional shift in the Collem-ola community in the sense of trait CWMs, testate amoebae thatere sampled from the irrigated plots in this study did show airectional ‘trait’ shift. Species that were wedge-shaped seemedo be more vulnerable to the physical impacts of the opposedxtreme precipitation events than other shaped species, poten-ially due to an increased vulnerability to flushing (Tsyganov et al.,013). This difference between the effect of flushing on testatemoebae and Collembola might be explained by the difference inaximum body size of these two groups (approximate maximum
ody size: (a) testate amoebae: 10–300 �m (Bobrov and Mazei,004); (b) Collembola: 0.1–4 mm (Table 1) and the approximateore size of the S. fuscum peat: 10–500 �m (McCarter and Price,012)). Whereas testate amoebae might indeed have been ‘flushed’hrough the pores during the extreme rain events, this physicalmpact did not affect Collembola, which also by leg force mightesist sudden flushes of water.
.4. Conclusions and ecological implications
Although recent studies reveal that altered precipitationegimes in the arctic can have significant impacts on ecosys-ems (Callaghan et al., 2010) this study shows that a subarcticmbrotrophic peatland Collembola community seems to be veryobust to these extreme events. The lack of response in this ecosys-em is most likely related to the fact that longer-term soil moistureonditions in the layer inhabited by Collembola did not change as
result of an increase in extreme summer rain events, due to theydrological properties of the Sphagnum mosses. What does this
mply for the effects of an increase in extreme precipitation eventsn C cycling in these systems? Although Collembola are not thenly soil fauna group involved in C and N cycling in northern peat-ands, they are central players in these soils (Woodin and Marquis,997) and their activities connect them with all trophic levels in theelowground food web (Berg et al., 2001; Filser, 2002). Changes inollembola community structure therefore might reflect a change
n ecosystem functioning. In this system no changes in Collem-ola density, species composition or CWMs were observed as aesult of extreme precipitation changes. This is in line with theack of response of the induced increase in extreme precipita-ion on Sphagnum and vascular plant productivity (Keuper et al.,012) and vegetation composition at the studied site (Keuper et al.npublished data). The lack of response of the key-player in thiselowground foodweb as well as the plant community to sim-lated extreme precipitation events indicate that these climatic
hanges will most likely not have big impacts on ecosystem func-ioning of subarctic ombrotrophic peatlands. Given the importancef these ecosystems for the global C balance and the current lack ofata on ecosystem responses to altered precipitation regimes, our
ology 79 (2014) 70–76 75
findings are an important contribution to the current knowledge ofthe ecological impact of future climate scenarios.
Acknowledgements
We would like to thank the Abisko Scientific Research Stationand The Climate Impact Research Centre of Umeå University (CIRC),for providing research facilities and hospitality. This study wasmade possible by funding of NWO (Netherlands Organization forScientific Research), specifically by its International Polar Yearprogram (ENVISNAR project) through grant 851.40.060 and bythe European Science Foundation (ESF) through the CLIMMANIResearch Networking Programme (http://www.esf.org/climmani)(E. Krab). Financial support was offered to F. Keuper by the DarwinCentre for Biogeosciences (Grant 142.161.042) and ANS Scholar-ship 2008, and to R. Aerts by the Dutch Polar Program (ALW-NPPGrant 851.30.023) and the EU-ATANS (Grant FP6 506004).
Appendix A. Supplementary data
Supplementary data associated with this article can befound, in the online version, at http://dx.doi.org/10.1016/j.apsoil.2014.03.007.
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