Alpine Fen Research Articles

The CSR strategies of alpine plants and community functional diversity in the Eastern Qinghai-Tibetan mountains

Many alpine communities of the Tibetan plateau experience both harsh climates and heavy grazing, and the adaptations to such environment are realized in plant functional traits and strategies. We tested, which leaf traits allow to dominate in the two wide-spread alpine communities of the Eastern Qinghai-Tibetan mountains, Kobresia alpine meadows and alpine fens, and do meadows and fens differ by community-weighted dominance-linked traits, strategy affinities, and functional diversity. Lower leaf dry matter content (LDMC) and higher specific leaf area (SLA) provides the species dominance in Kobresia alpine meadows, while size traits do not influence the dominance. Both LDMC and SLA have low functional evenness and divergence in the two communities. The prevail of stress-tolerators reflects the abiotic environment of alpine plants, but high affinities to ruderal strategy are possibly related to grazing.

Methane emissions during different freezing-thawing periods from a fen on the Qinghai-Tibetan Plateau: Four years of measurements

How methane (CH4) fluxes from alpine peatlands, especially during freeze-thaw cycles, affect the global CH4 budget is poorly understood. The present research combined the eddy covariance method, incubation experiments and high-throughput sequencing to observe CH4 flux from an alpine fen during thawing-freezing periods over a period of four years. The response of CH4 production potential and methanogenic archaea to climate change was analyzed. We found a relatively high mean annual cumulative CH4 emission of 37.7 g CH4-C m−2. The dominant contributor to CH4 emission was the thawing period: warmer, longer thawing periods contributed 69.1-88.6% to the annual CH4 budget. Non-thawing periods also contributed, with shorter frozen-thawing periods accounting for up to 18.5% and shorter thawing-freezing periods accounting for up to 8.8%. Over the course of a year, emission peaked in the peak growing season and at onset of thawing and freezing. In contrast, emission did not vary substantially during the frozen period. Daily mean emission was highest during the thawing period and lowest during the frozen period. Diurnal patterns of CH4 emission were similar among the four periods, with peaks ranging from 12:00 to 18:00 and the lowest emission around 00:00. Water table and temperature were the dominant factors controlling CH4 emissions during different thawing-freezing periods. Our results suggest that CH4 emission from peatland will change substantially as CH4 production, microbial composition, and patterns of thawing-freezing cycles change with global warming. Therefore, frequent monitoring of CH4 fluxes in more peatlands and in situ monitoring of methanogenesis and related microbes are needed to provide a clear picture of CH4 fluxes and the thawing-freezing processes that affect them.

Clonal diversity and genetic variation of the sedge Carex nigra in an alpine fen depend on soil nutrients.

In this study we analysed the impact of water regime and soil nutrients on the clonal diversity and genetic variation of the sedge Carex nigra in a central alpine fen. For our analysis, we established 16 study plots randomly distributed over the fen. We determined the exact elevation of each plot as an indicator for the water regime and measured the content of phosphorous and potassium in the soil of each plot. Clonal diversity and genetic variation of C. nigra were assessed with nuclear microsatellites using leaf material collected in 20 subplots along a diagonal cross within each study plot. The influence of water regime and soil mineral nutrients on clonal diversity and genetic variation was estimated by Bayesian multiple regression. Our study revealed a clear impact of soil nutrient conditions on clonal diversity and genetic variation of C. nigra, which increased with the concentration of phosphorous and decreased with the concentration of potassium. Key background to these findings seems to be the relative offspring success from generative as compared to clonal propagation. Phosphorous acquisition is essential during seedling establishment. Clonal diversity and genetic variation increase, therefore, at sites with higher phosphorous contents due to more successful recruitment. High levels of clonal diversity and genetic variation at sites of low potassium availability may in contrast be mainly caused by increased plant susceptibility to abiotic stress under conditions of potassium deficiency, which brings about more gaps in C. nigra stands and favors the ingrowth from other clones or recruitment from seeds.

Annual methane emissions from degraded alpine wetlands in the eastern Tibetan Plateau

Grazing-oriented drainage of alpine/boreal wetlands has been broadly implemented to meet the increasing demand for animal products. However, the annual methane (CH4) emissions from alpine fens degraded due to drainage for grazing have not been well characterized due to a lack of year-round observations. In this study, the year-round CH4 fluxes from a degraded alpine fen that is typical in the Tibetan Plateau (TP) were measured. The temperature sensitivity of the CH4 emissions during the nongrowing season (NGS) was different between the microsites with and without CH4 uptake during the growing season (GS), showing apparent activation energy of 59–61 vs. 22–43 kJ mol−1 (or variation folds induced by the 10-degree change (i.e., Q10): 2.61–2.74 vs. 1.38–1.91). The CH4 emissions amounted to 0.2–63.3 kg C ha−1 yr−1 (with −0.8 to 41.4 kg C ha−1 and 0.9 to 21.9 kg C ha−1 in the GS and NGS, respectively), which were significantly (P < 0.05) related to the distances to the drainage ditch or water tables across the six microsites. As a key factor, the water table determined the role of the CH4 emissions during freezing/thawing. For cool/cold/alpine wetlands with no CH4 uptake in the GS, a mean factor of 1.52 (within a range of 1.00–2.44 at the 95% confidence interval), corresponding to an NGS contribution of 34% (ranging from 0 to 59%), was recommended to upscale the GS emissions to annual totals. Degradation of the native peat marshes in the Zoige region (originally the largest area of alpine wetlands) due to intentional drainage has greatly reduced the quantities of CH4 emissions. Additional studies are still needed to minimize the large uncertainties in CH4 emissions estimates for the changes in alpine wetlands in this region and for the entire TP.

Environmental drivers of subalpine and alpine fen vegetation in the Southern Rocky Mountains, Colorado, USA

Fens are widely distributed wetlands worldwide and provide vital habitat for plant and animal species in mountainous regions. Alpine fens are rare in the Rocky Mountains and concentrated in the San Juan Mountains where broad regions at high elevation have relatively level topography and suitable climate to favor peat accumulation. Studies of montane and boreal peatlands have identified water chemistry as a main driver of vegetation composition. This study investigated whether similar drivers of vegetation composition are important for alpine and subalpine fens in the San Juan Mountains of Colorado, USA. Water chemistry variables were most important in structuring subalpine and alpine fen vegetation. However, these variables explained considerably less variation in alpine than subalpine fen vegetation. In addition, lower variance of water chemistry in alpine fens did not lead to lower beta diversity of vegetation in alpine than in subalpine fens. Although alpine and subalpine fen vegetation supports similar beta diversity, key differences occur in the environmental drivers of their vegetation composition.

Diurnal Patterns of Greenhouse Gas Fluxes in a Swiss Alpine Fen

Diurnal patterns of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) net fluxes were studied in a permanently submerged, Carex rostrata dominated Swiss alpine fen. Fluxes were measured in August and September using static chambers. Methane was emitted at all six time points analysed during each diurnal cycle with little variation between day, night or twilight (8.3 ± 0.8 mg m−2h−1 in August). The fen was a nighttime CO2 source (138 ± 46 mg m−2h−1) and generally a daytime CO2 sink. Uptake of CO2 varied with light intensity (98 ± 57 to 391 ± 43 mg m−2h−1 in August), but light saturation of photosynthesis was apparent at low irradiation levels. Emission or uptake of N2O was not discerned. In September, CH4 and CO2 fluxes were generally lower compared with August, compliant with less green C. rostrata biomass. Diurnal changes in subsurface properties were minor with little influence on the diurnal patterns. Temperature dependency of CH4 and CO2 emissions was apparent under controlled conditions using C. rostrata monoliths. In August, the fen showed highest photosynthetic rates and was a net carbon sink (50 mmol m−2day−1), but high CH4 emissions resulted in the fen being a net source of 250 mmol CO2 equivalents m−2day−1.

Maintain Spatial Heterogeneity, Maintain Biodiversity—A Seed Bank Study in a Grazed Alpine Fen Meadow

AbstractWetland degradation is a source of anxiety and is more severe in cold regions than other areas. The soil seed bank acts as a propagule source for revegetation to affiliate the restoration of degraded wetlands. However, the effects of this approach are controversial and depend on the traits of the seed bank and its interactions with the environment. The seed bank in an alpine fen meadow was studied to determine its exact role in revegetation. The surveyed shore of a Tibetan lake, Gahai Lake, was divided into three sites under different levels of grazing pressure. Each site was separated into six transects along a water‐depth gradient to collect soil cores to determine the pattern of biodiversity through a germination experiment in a greenhouse. After an analysis of heterogeneity‐related diversity, partitioning of 58 discovered species indicated that 39.5 could be contributed to beta‐diversity, which was mainly contributed to water depth. Overgrazing (0.607 sheep unit/acre, November—March) decreased seed bank diversity in many respects, especially through decreasing spatial heterogeneity and homogenizing biota. A lightly grazed, well‐protected site had not only the highest beta‐diversity and species abundance but also the highest inter‐site species turnover rate compared with other sites under moderate grazing intensity. Despite the lack of target species, the seed bank serves as (i) a species‐rich pool; (ii) an extant legacy seed source for sustaining heterogeneity and floristic diversity; and (iii) an ecological indicator, and its effect can be reinforced by appropriate grazing practices (multiple intensity) and hydrological modifications. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Methane and Carbon Dioxide Fluxes from a European Alpine Fen Over the Snow-Free Period

Wetlands play an important role in the global carbon cycle and are sources and sinks for the greenhouse gases methane (CH4) and carbon dioxide (CO2). We provide an in situ study on variability of daytime CH4 emissions and net ecosystem CO2 exchange (NEE) from a permanently submerged, Carex rostrata dominated Swiss alpine fen over the snow-free period (June–October). Flux chamber measurements were combined with analyses of above-ground biomass and physico-chemical pore water properties. The fen was a net daytime CH4 source throughout the snow-free period, and emissions varied significantly between the sampling dates, ranging from 3.1 ± 0.9 mg CH4 m−2 h−1 in October to 8.0 ± 2.9 mg CH4 m−2 h−1 in August. The fen was generally a daytime sink for CO2, and net CO2 emission was only observed in late October. Variations in NEE were more pronounced than variations in CH4 emissions, but both fluxes correlated with changes in green C. rostrata biomass and subsurface temperatures. Methane and CO2 pore water concentrations also varied significantly over the snow-free period, decreasing and increasing, respectively. These variations were linked to the development of biomass, but CH4 emissions and NEE were not correlated with the respective pore water concentrations.

Methanotrophic and Methanogenic Communities in Swiss Alpine Fens Dominated by Carex rostrata and Eriophorum angustifolium.

Vascular plants play a key role in controlling CH4 emissions from natural wetlands, because they influence CH4 production, oxidation, and transport to the atmosphere. Here we investigated differences in the abundance and composition of methanotrophic and methanogenic communities in three Swiss alpine fens dominated by different vascular plant species under natural conditions. The sampling locations either were situated at geographically distinct sites with different physicochemical properties but the same dominant plant species (Carex rostrata) or were located within the same site, showing comparable physicochemical pore water properties, but had different plant species (C. rostrata or Eriophorum angustifolium). All three locations were permanently submerged and showed high levels of CH4 emissions (80.3 to 184.4 mg CH4 m(-2) day(-1)). Soil samples were collected from three different depths with different pore water CH4 and O2 concentrations and were analyzed for pmoA and mcrA gene and transcript abundance and community composition, as well as soil structure. The dominant plant species appeared to have a significant influence on the composition of the active methanotrophic communities (transcript level), while the methanogenic communities differed significantly only at the gene level. Yet no plant species-specific microbial taxa were discerned. Moreover, for all communities, differences in composition were more pronounced with the site (i.e., with different physicochemical properties) than with the plant species. Moreover, depth significantly influenced the composition of the active methanotrophic communities. Differences in abundance were generally low, and active methanotrophs and methanogens coexisted at all three locations and depths independently of CH4 and O2 concentrations or plant species.

Alpine plant communities of Tibet and Caucasus: in quest of functional convergence

ABSTRACT We compared aboveground phytomass structure and community weighed mean leaf traits (leaf area and specific leaf area) in alpine plant communities of Tibet (alpine shrub meadows and alpine bogs, grazed and fenced) and the Caucasus (al­pine lichen heaths, Festuca varia grasslands, Geranium ­ Hedysarum meadows, alpine snowbeds and alpine fens). We tested, if (1) the communities at least partly show functional convergence, (2) the mean community biomass weighed traits vary in accordance with position along a catena, and (3) grazing influences community functional structure. To reveal the pattern of functional structure we run Detren­ded Correspondence Analysis with the biomass of functional groups as variables and plots as cases. Position along a catena was the main driver, and the alpine fens of both Tibet and the Caucasus were the most similar in functional structure. Community biomass weighed specific leaf area increased with water availability and from grass­dominated to frequently disturbed forb­dominated communities.

Methane dynamics in an alpine fen: a field-based study on methanogenic and methanotrophic microbial communities.

Wetlands are important sources of the greenhouse gas methane (CH4). We provide an in situ study of CH4 dynamics in the permanently submerged soil of a Swiss alpine fen. Physico-chemical pore water analyses were combined with structural and microbiological analyses of soil cores at high vertical resolution down to 50 cm depth. Methanotrophs and methanogens were active throughout the depth profile, and highest abundance of active methanotrophs and methanogens [6.1 × 10(5) and 1.1 × 10(7) pmoA and mcrA transcripts (g soil)(-1), respectively] was detected in the uppermost 2 cm of the soil. Active methanotrophic communities in the near-surface zone, dominated by viable mosses, varied from the communities in the deeper zones, but further changes with depth were not pronounced. Apart from a distinct active methanogenic community in the uppermost sample, a decrease of acetoclastic Methanosaetaceae with depth was observed in concomitance with decreasing root surface area. Overall, root surface area correlated with mcrA transcript abundance and CH4 pore water concentrations, which peaked (137.1 μM) at 10 to 15 cm depth. Our results suggest that stimulation of methanogenesis by root exudates of vascular plants had a stronger influence on CH4 dynamics than stimulation of CH4 oxidation by O2 input.

Plant community responses to five years of simulated climate warming in an alpine fen of the Qinghai–Tibetan Plateau

Background: Alpine and arctic ecosystems at high latitudes have been shown to be particularly vulnerable to climate change, but little has been reported about plant community responses from lower latitudes, such as the vast Qinghai–Tibetan Plateau.Aim: To examine how alpine fen plant community species richness, diversity, cover, above- and below-ground biomass, and how the abundance of two sedges, the dominant Kobresia tibetica and the subordinate Carex moorcroftii, respond to experimental warming.Methods: We used open-top chambers of two heights, with identical open-top area, to simulate two levels of experimental warming at 4700 m on the Qinghai–Tibetan Plateau.Results: Five years of experimental warming reduced species richness and diversity, primarily due to a decrease in the diversity of graminoids. Above-ground biomass, vegetation height and cover increased at both levels of warming. Below-ground biomass increased at a depth of 5–20 cm, but not at 0–5 cm, indicating an allocation of resource to plant roots in deeper soils.Conclusion: The different responses to warming between the two graminoids in the study suggest that further studies on species-specific responses are needed to understand the regional differences observed in response to long-term warming. Our study also documented a decline in species richness and diversity in the control plots during the five-year experimental period which, together with results from other studies in this region, suggests that the alpine fens are already changing in response to the on-going climate warming in this area.

Spatial variability of methane emissions from Swiss alpine fens

Wetland ecosystems are a major natural source of the important greenhouse gas methane (CH4). Among these ecosystems, fens have been shown to release high quantities of CH4. Data on CH4 emissions from alpine fens are scarce and mainly limited to the United States and China. Therefore, static chambers were used to quantify CH4 emissions from 14 fens located in the Swiss Alps. The aims of this study were to determine the spatial variability of the emissions and to identify potential key factors which influence CH4 turnover. The fens were located at altitudes between 1,800 and 2,600 m a.s.l., the pore water varied from acidic to slightly acidic (pH 4.5–6.4) and the vegetation was dominated by plants of the genus Carex. In addition, the underlying bedrock was either siliceous or calcareous. Methane emissions ranged from 74 ± 43 to 711 ± 212 mg CH4 m−2 day−1. The type of bedrock, the plant biomass above the water table and the CH4 pore water concentrations at depths from 0 to 20 cm were the main factors influencing CH4 emissions. Detailed measurements in three selected fens suggested that more than 98 % of the total CH4 emissions are due to plant-mediated transport.

Life-form composition of alpine plant communities at the Eastern Qinghai-Tibetan plateau

Alpine plants of the eastern Qinghai-Tibetan plateau (Sichuan, China) are developed under long-lasting grazing by wild and domestic yaks. Among morphological features of plants, life forms may reflect their adaptation to grazing. We studied life-form composition of four typical communities within the alpine belt (3930–3960 m a.s.l.) subjected to grazing of various intensity: alpine fen (heavily grazed), alpine shrub meadow (heavily grazed), Spiraea alpina thicket (grazed), and Rhododendron thicket (practically not grazed). The following morphological traits were studied: (1) life form according to Raunkiaer, (2) life form according to Serebryakov, (3) canopy structure, and (4) rate of lateral spreading. We derived life-form spectra based on (1) the number of species per life form and (2) the cumulative abundance of species which have the same life form. One-way ANOVA and nonparametric ANOVA were run to test for significance of differences between spectra. The studied communities differed significantly by the proportion of different life forms. The main life forms are caudex and short rhizome hemicryptophytes, nonclonal species, or species with a low rate of lateral spreading. Therophytes made up 10–11% of the communities except in Rhododendron thickets, where such were absent. These life forms can indicate grazing in the study area.

Vegetation–environment relationships in alpine mires of the West Carpathians and the Alps

AbstractQuestionsHow do two distant mountain ranges differ in their vegetation–environment relationships, overall species composition and its variability and species richness of vascular plants and bryophytes in alpine fens and bogs? Is the floristic difference consistent along the acidity–alkalinity gradient?LocationWest Carpathians (Poland, Slovakia) and Swiss Alps.MethodsVascular plant and bryophyte species compositions and environmental characteristics were sampled along the large acidity–alkalinity gradient within the alpine belts. PERMANOVA was used for testing floristic differences between the regions, DCA for the patterns description, CCA for testing the vegetation–environment relationships and linear models for testing the local species richness determinants. Compositional β‐diversity (rate of compositional turnover) and regional species pool were compared using PERMDISP and sample‐based rarefaction curves.ResultsMost floristic variation was explained by water pH in both regions. Macroclimate was the second most important gradient in the Alps, correlating with the second DCA axis delimiting the moderately poor brown‐moss fens from the Sphagnum bogs. The species composition differed significantly between the regions in all three pH classes, expect for bryophytes in the middle pH class. Bryophytes exhibited higher similarities between the regions, except in acidic mires. Vascular plant composition differed most in the middle pH class. The local species richness was predominantly determined by pH, except for bryophytes in the Alps. As compared to bryophytes, vascular plant local species richness was affected by more factors and showed a clear linear response to pH. Within the particular pH classes, there were few differences in local species richness, compositional β‐diversity and regional species pool between the two mountain ranges.ConclusionsThe pattern in inter‐regional floristic dissimilarities differs between bryophytes and vascular plants, probably because of better dispersal ability of bryophytes, and different causes of these dissimilarities: lower mass effect at extreme ends of the acidity–alkalinity gradient in the case of vascular plants and higher compositional β‐diversity of acidic mires in the case of bryophytes. Contrary to previously explored alpine springs of the same regions, local species richness and composition were determined rather by pH than mineral richness, and all patterns were more consistent between the regions and the taxonomic groups.

Spatial Genetic Structure of the Sedge Carex Nigra Reflects Hydrological Conditions in an Alpine Fen

Fine-scale genetic structure of plant populations depends on several ecological processes. In this study, we analyzed the impact of hydrological heterogeneity on the spatial genetic structure of the wind-pollinated black sedge Carex nigra in an alpine fen. We performed amplified fragment length polymorphisms (AFLPs) with 111 samples collected along a grid covering the whole area of the fen and studied fine-scale genetic structure using spatial autocorrelation and Bayesian cluster analyses. We observed a significant spatial genetic structure indicating isolation-by-distance, which can be ascribed to restricted seed dispersal. Bayesian cluster analysis revealed four groups of genetically related and patchy distributed samples within the fen. Two of these groups were distributed in the deeper and moister regions of the fen, while the two other groups were spatially restricted to the higher and drier regions of the fen. We think that the observed pattern of spatial genetic variation reflects hydrological heterogeneity within the fen and conclude that the four groups represent cohorts of individuals originating from different recruitment events in different parts of the fen. Genetic variation was much lower in the groups from the drier regions of the fen. Since Carex species require moist conditions for germination and establishment, the low level of genetic variation can most likely be ascribed to restricted seedling recruitment in the drier regions of the fen. Habitat heterogeneity affects, therefore, both spatial genetic structure and levels of genetic variation. This study clearly demonstrates that integrating fine-scale genetic analyses with complementary biological data can markedly improve the identification of processes that shape fine-scale genetic structure within plant populations.

Methane emissions from an alpine fen in central Switzerland

Methane emissions and below ground methane pore water concentrations were determined in an alpine fen at 1,915 m a.s.l. in central Switzerland. The fen represented an acidic (pH 4.5–4.9), nutrient-poor to mesotrophic habitat dominated by Carex limosa, Carex rostrata, Trichophorum caespitosum and Sphagnum species. From late fall to late spring the fen was snow-covered. Throughout winter the temperatures never dropped below 0°C at 5 cm below the vegetation surface. Methane emissions in June, July, August and September were in the range of 125 (±26)–313 (±71) mg CH4 m−2 day−1 with a tendency to decrease along the summer season. Mean methane pore water concentrations at a depth of 20–40 cm below the vegetation surface were 526 (±32) μM in June and in the range of 144 (±10)–233 (±7) μM in July, August and September. At a depth of 0–20 cm the mean methane pore water concentrations dropped back to <20 μM with an almost linear decrease between 0 and 15 cm. Oxygen pore water concentrations were close to air saturation in the first few centimeters and dropped back below detection limit at a depth of 20 cm. In July and August the pore water concentrations of dissolved organic carbon (DOC) were in the range of 7.2–10.1 mg C l−1 at all depths. The pore water concentrations of acetate, formate and oxalate were in the range of 2.0–8.2 μM at all depths. Methanotrophic and methanogenic communities were quantified using pmoA and mcrA, respectively, as marker genes. The abundances of both communities showed a distinct peak at a depth of 10–15 cm below the vegetation surface.

Effects of short-term drying and irrigation on CO2 and CH4 production and emission from mesocosms of a northern bog and an alpine fen

Atmospheric CO2 and CH4 exchange in peatlands is controlled by water table levels and soil moisture, but impacts of short periods of dryness and rainfall are poorly known. We conducted drying-rewetting experiments with mesocosms from an ombrotrophic northern bog and an alpine, minerotrophic fen. Efflux of CO2 and CH4 was measured using static chambers and turnover and diffusion rates were calculated from depth profiles of gas concentrations. Due to a much lower macroporosity in the fen compared to the bog peat, water table fluctuated more strongly when irrigation was stopped and resumed, about 11 cm in the fen and 5 cm in the bog peat. Small changes in air filled porosity caused CO2 and CH4 concentrations in the fen peat to be insensitive to changes in water table position. CO2 emission was by a factor of 5 higher in the fen than in the bog mesocosms and changed little with water table position in both peats. This was probably caused by the importance of the uppermost, permanently unsaturated zone for auto- and heterotrophic CO2 production, and a decoupling of air filled porosity from water table position. CH4 emission was 12.6 mmol m−2 day−1 in the fen peat, where it was lowered by water table fluctuations. CH4 production was limited to the saturated zone in the bog peat but proceeded in the capillary fringe of the fen peat. Water table drawdown partly led to inhibition of methanogenesis in the newly unsaturated zone, but CH4 production appeared to continue after irrigation without time-lag. The identified effects of irrigation on soil moisture and respiration highlight the importance of peat physical properties for respiratory dynamics; but the atmospheric carbon exchange was fairly insensitive to the small-scale fluctuations induced.

Effects of Short-Term Drying and Irrigation on Electron Flow in Mesocosms of a Northern Bog and an Alpine Fen

Methane emissions and element mobility in wetlands are controlled by soil moisture and redox conditions. We manipulated soil moisture by weekly drying and irrigation of mesocosms of peat from a bog and iron and sulfur rich fen. Water table changed more strongly in the decomposed fen peat ( approximately 11 cm) than in the fibric bog peat ( approximately 5 cm), where impacts on redox processes were larger due to larger change in air filled porosity. Methanogenesis was partly decoupled from acetogenesis and acetate accumulated up to 5.6 mmol L(-1) in the fen peat after sulfate was depleted. Irrigation and drying led to rapid redox-cycles with sulfate, hydrogen sulfide, nitrate, and methane being produced and consumed on the scale of days, contributing substantially to the total electron flow and suggesting short-term resilience of the microbial community to intermittent aeration. Anaerobic CO2 production was partly balanced by methanogenesis (0-34%), acetate fermentation (0-86%), and sulfate reduction (1-30%) in the bog peat. In the fen peat unknown electron acceptors and aerenchymatic oxygen influx apparently drove respiration. The results suggest that regular rainfall and subsequent drying may lead to local oxidation-reduction cycles that substantially influence electron flow in electron acceptor poor wetlands.

Interannual Ecosystem CO2 Dynamics in The Alpine Zone of The Eastern Alps, Austria

ABSTRACTInformation about the annual carbon fluxes of fen and meadow ecosystems in alpine environments is rare. We studied the influence of photosynthetic active radiation (PAR), plant green area index (GAI), soil temperature, and water-filled pore space (wfps) on the net CO2 emission at four alpine sites (one meadow and three fen sites) differing in water balance and plant community. Measurements over two years were made in the Eastern Alps, Austria, including two snow-free periods and two snow periods. During snow-free periods, net CO2 gain during daylight periods (NEElight , PAR > 0) depended on PAR and GAI. The net CO2 emission rate at night (Rtot , PAR = 0) was positively related to soil temperature, while low wfps reduced the carbon loss via Rtot of the meadow and driest fen study site but reinforced carbon loss of the wetter fen sites. Daily average ecosystem net CO2 gain (NEEday ) during snow-free periods (averaged over both years) at the meadow was 3.5 g CO2 m−2 d−1 and ranged from 1.5 to 3.4 g CO2 m−2 d−1 at the fen sites. Mean average daily wintertime CO2 emission was low, being only −0.9 g CO2 m−2 d−1 for meadow and between −0.2 and −0.7 g CO2 m−2 d−1 for all fen sites. All sites function as significant annual net carbon sinks, with a net carbon gain from 50 to 121 g C m−2 a−1 (averaged over both years) irrespective of water balance. Our results indicate that these alpine fen sites that have built up a large carbon stock in the past do not gain a further carbon surplus compared with the meadow under the current climate.