The role of Eriophorum vaginatum in CH4 flux from an ombrotrophic peatland

Vegetation composition was found to be an important factor controlling CH₄ emission from an ombrotrophic peatland in the UK, with significantly greater (P < 0.01) CH₄ released from areas containing both Eriophorum vaginatumL. and Sphagnum, than from similar areas without E. vaginatum. Positive correlations were observed between the amount of E. vaginatum and CH₄ emission, with the best predictor of flux being the amount of below-ground biomass of this species (r ² = 0.93). A cutting experiment revealed that there was no significant difference (P > 0.05) in CH₄ flux between plots with E. vaginatum stems cut above the water table and plots with intact vegetation, yet there was a 56% mean reduction in CH₄ efflux where stems were cut below the water table (P < 0.05). The effect of E. vaginatum on CH₄ release was mimicked by the presence of inert glass tubes. These findings suggest that the main short-term role of E. vaginatum in the ecosystem is simply as a conduit for CH₄ release. The longer-term importance of E. vaginatum in controlling CH₄ fluxes through C substrate input was suggested by the positive correlation between the night-time CO₂ and CH₄ fluxes (r ² = 0.70), which only occurred when the vegetation was not senescent. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Rewetting Measures in Dutch Raised Bog Remnants on Assemblages of Aquatic Rotifera and Microcrustaceans

Species differ in their life cycle, habitat demands and dispersal capacity. Consequently different species or species groups may respond differently to restoration measures. To evaluate effects of restoration measures in raised bog remnants on aquatic microinvertebrates, species assemblages of Rotifera and microcrustaceans were sampled in 10 rewetted and 10 non-rewetted sites, situated in 7 Dutch raised bog remnants. A total of 129 species (Rotifera 108, Cladocera 15, Copepoda 6 species) were found. The species assemblages, total numbers of species and numbers of characteristic raised bog species did not differ between the 10 rewetted and 10 non-rewetted sites. The dominant pattern in the variation in microinvertebrate assemblages could be explained by the presence or absence of open water and variation in physico-chemical variables of surface water and organic matter. Furthermore, the species assemblages of water bodies situated in the same area were on average more similar to each other than to assemblages from other areas. These differences between areas may be due to differences in environmental conditions of water bodies, and possibly also to differences in the local species pool and the subsequent immigration sequence of species. We conclude that, in contrast to earlier findings on aquatic macroinvertebrates, populations of microinvertebrate species, including characteristic species, can either persist in the raised bog remnants during the process of rewetting or (re-)establish within a relatively short period of time (less than about 5 years).     

青藏高原泥炭地水位下降促进土壤碳积累的影响机制

酚类物质作为泥炭地重要的碳分解抑制剂,植被作为泥炭地关键的碳输入来源,它们在土壤碳(可溶性有机碳(DOC)等)周转过程中都发挥着重要作用。然而,目前关于植被群落结构、酚类物质以及DOC含量对水位波动的响应存在较大争议。因此,为明确泥炭地水位下降对植被群落结构、酚类物质以及DOC含量的影响并探明三者间的潜在联系,以若尔盖高原泥炭地作为研究对象,选取红原县日干乔地区3处不同地下水位泥炭地(水位由高到低依次为S1(-1.9 cm)、S2(-10 cm)、S3(-19 cm)样地),调查不同水位条件下植被群落结构特征,并探究酚类物质及土壤碳含量对水位波动的响应。结果表明:(1)从S1到S3样地水位下降促进土壤DOC显著增加(P<0.05),土壤总碳从S1到S2显著增加(P<0.05),而从S2到S3无显著差异;(2)泥炭地水位下降促使禾本科(发草Deschampsia cespitosa)、莎草科(木里薹草Carex muliensis、乌拉草Carex meyeriana)植物大量出现,植被群落高度显著增加(P<0.05)。植被群落地上生物量由153.67 g/m~2增加至...     

Carbon preservation in humic lakes; a hierarchical regulatory pathway

Peatland catchments store vast amounts of carbon. Humic lakes and pools are the primary receptacles for terrigenous carbon in these meta‐ecosystems, representing sequestration hotspots; boreal lakes alone store ca. 120 Pg C. But little is known about the mechanisms that preserve aquatic carbon stocks. Here, we determined the regulatory pathway of decomposition in relation to ‘traditional’ limitations, namely anoxia, decay inhibiting compounds, low nutrients and acidity, using in vitro manipulation, mesocosms and natural gradients. We show that anoxia represents a powerful hierarchical preservation mechanism affecting all major limitations on decomposition and recapturing carbon that would otherwise escape from peatlands. Oxygen constraints on microbial synthesis of oxidases and nutrient‐cycling enzymes, prevents the decay of organic matter to CO₂, CH₄ and N₂O by allowing inhibitor accumulation and lowering nutrients. However, this pathway is sensitive to direct nutrient inputs and therefore eutrophication could initiate catastrophic feedback to global warming via dramatically increased greenhouse gas emissions. Identifying these process‐specific limitations should inform better management and conservation of these vital systems.     

Hot spots for nitrous oxide emissions found in different types of permafrost peatlands

Recent findings on large nitrous oxide (N₂O) emissions from permafrost peatlands have shown that tundra soils can support high N₂O release, which is on the contrary to what was thought previously. However, field data on this topic have been very limited, and the spatial and temporal extent of the phenomenon has not been known. To address this question, we studied N₂O dynamics in two types of subarctic permafrost peatlands, a peat plateau in Russia and three palsa mires in Finland, including also adjacent upland soils. The peatlands studied have surfaces that are uplifted by frost (palsas and peat plateaus) and partly unvegetated as a result of wind erosion and frost action. Unvegetated peat surfaces with high N₂O emissions were found from all the studied peatlands. Very high N₂O emissions were measured from peat circles at the Russian site (1.40±0.15 g N₂O m^?2 yr^?1). Elevated, sparsely vegetated peat mounds at the same site had significantly lower N₂O release. The N₂O emissions from bare palsa surfaces in Northern Finland were highly variable but reached high rates, similar to those measured from the peat circles. All the vegetated soils studied had negligible N₂O release. At the bare peat surfaces, the large N₂O emissions were supported by the absence of plant N uptake, the low C : N ratio of the peat, the relatively high gross N mineralization rate and favourable moisture content, together increasing availability of mineral N for N₂O production. We hypothesize that frost heave is crucial for high N₂O emissions, since it lifts the peat above the water table, increasing oxygen availability and making it vulnerable to the the physical processes that may remove the vegetation cover. In the future, permafrost thawing may change the distribution of wet and dry surfaces in permafrost peatlands, which will affect N₂O emissions.     

Moss Regeneration for Fen Restoration: Field and Greenhouse Experiments

Fen bryophytes are an important component of natural fens and should be included in fen restoration projects. The goal of this study was to examine the regeneration capabilities of nine bryophytes common to moderate-rich and poor fens in North America. A greenhouse experiment was carried out to examine the limitations and optima for the regeneration of fen bryophytes under different light and water regimes. A field experiment tested these same bryophytes in the presence of three potential nurse-plants. In the greenhouse experiment, the presence of shade increased regeneration success for eight out of nine species. A high water level was ideal for the regeneration of the majority of species tested. In the field experiment, Sphagnum species had the highest regeneration, and all species had higher regeneration under a dense canopy of herbaceous plants. Fen bryophytes show good potential for use in restoration projects because the tested bryophytes regenerated well from fragments.     

The Effects of pH on a Periphyton Community in an Acidic Wetland, USA

Despite the importance of peatlands, the algal ecology of peatlands and the periphyton communities which are abundant in these habitats are relatively understudied. We performed an in situ manipulation of pH in an intermediate fen in northern lower Michigan in order to examine how hydrogen ion concentrations structure an epiphytic algal community. Levels of pH were manipulated in enclosures from the control level (pH = 5) to an acid treatment (pH = 4) by adding H₂SO₄ and a neutral treatment (pH = 7) by adding NaOH. Algal communities growing on sections of Chamaedaphne calyculata (L.) Moench stems were examined after 22 days of colonization. Chlorophyll a concentration was significantly greater only in the acid treatment (~5.5 mg m⁻²) relative to the control (~3.5 mg m⁻²). Taxa richness was lower in the acid treatment. The algal assemblages were dominated by filamentous green algae and a filamentous taxon, Mougeotia spp., was significantly greater in the acid treatment relative to the control. Increases in Zygnemataceae and Oedogonium spp. most likely account for the higher chlorophyll a in the acid treatment. Most treatment differences were detected in the neutral treatment, including increased abundances of Closterium polystichum Nygaard, Cosmarium sp., Peridinium inconspicuum Lemmermann, and Synedra acus Kütz. Unexpectedly, there was no strong response of the desmid community. These data can be informative in the development of algal monitoring programs in peatlands when assessment of acidification is desired.     

Two mire species respond differently to enhanced ultraviolet-B radiation: effects on biomass allocation and root exudation

Increased ultraviolet-B (UV-B) radiation arising from stratospheric ozone depletion may influence soil microbial communities via effects on plant carbon allocation and root exudation. Eriophorum angustifolium and Narthecium ossifragum plants, grown in peatland mesocosms consisting of Sphagnum peat, peat pore water and natural microbial communities, were exposed outdoors to enhanced UV-B radiation simulating 15% ozone depletion in southern Scandinavia for 8 wk. Enhanced UV-B increased rhizome biomass and tended to decrease the biomass of the largest root fraction of N. ossifragum and furthermore decreased dissolved organic carbon (DOC) and monocarboxylic acid concentration, which serves as an estimate of net root exudation, in the pore water of the N. ossifragum mesocosms. Monocarboxylic acid concentration was negatively related to the total carbon concentration of N. ossifragum leaves, which was increased by enhanced UV-B. By contrast, enhanced UV-B tended to increase monocarboxylic acid concentration in the rhizosphere of E. angustifolium and its root : shoot ratio. Microbial biomass carbon was increased by enhanced UV-B in the surface water of the E. angustifolium mesocosms. Increased UV-B radiation appears to alter below-ground biomass of the mire plants in species-specific patterns, which in turn leads to a change in the net efflux of root exudates.