Peatlands contain approximately one third of all soil organic carbon (SOC). Warming can alter above‐ and belowground linkages that regulate soil organic carbon dynamics and C‐balance in peatlands. ...Here we examine the multiyear impact of in situ experimental warming on the microbial food web, vegetation, and their feedbacks with soil chemistry. We provide evidence of both positive and negative impacts of warming on specific microbial functional groups, leading to destabilization of the microbial food web. We observed a strong reduction (70%) in the biomass of top‐predators (testate amoebae) in warmed plots. Such a loss caused a shortening of microbial food chains, which in turn stimulated microbial activity, leading to slight increases in levels of nutrients and labile C in water. We further show that warming altered the regulatory role of Sphagnum‐polyphenols on microbial community structure with a potential inhibition of top predators. In addition, warming caused a decrease in Sphagnum cover and an increase in vascular plant cover. Using structural equation modelling, we show that changes in the microbial food web affected the relationships between plants, soil water chemistry, and microbial communities. These results suggest that warming will destabilize C and nutrient recycling of peatlands via changes in above‐ and belowground linkages, and therefore, the microbial food web associated with mosses will feedback positively to global warming by destabilizing the carbon cycle. This study confirms that microbial food webs thus constitute a key element in the functioning of peatland ecosystems. Their study can help understand how mosses, as ecosystem engineers, tightly regulate biogeochemical cycling and climate feedback in peatlands
In northern peatlands, reduction of Sphagnum dominance in favour of vascular vegetation is likely to influence biogeochemical processes. Such vegetation changes occur as the water table lowers and ...temperatures rise. To test which of these factors has a significant influence on peatland vegetation, we conducted a 3‐year manipulative field experiment in Linje mire (northern Poland). We manipulated the peatland water table level (wet, intermediate and dry; on average the depth of the water table was 17.4, 21.2 and 25.3 cm respectively), and we used open‐top chambers (OTCs) to create warmer conditions (on average increase of 1.2°C in OTC plots compared to control plots). Peat drying through water table lowering at this local scale had a larger effect than OTC warming treatment per see on Sphagnum mosses and vascular plants. In particular, ericoid shrubs increased with a lower water table level, while Sphagnum decreased. Microclimatic measurements at the plot scale indicated that both water‐level and temperature, represented by heating degree days (HDDs), can have significant effects on the vegetation. In a large‐scale complementary vegetation gradient survey replicated in three peatlands positioned along a transitional oceanic–continental and temperate–boreal (subarctic) gradient (France–Poland–Western Siberia), an increase in ericoid shrubs was marked by an increase in phenols in peat pore water, resulting from higher phenol concentrations in vascular plant biomass. Our results suggest a shift in functioning from a mineral‐N‐driven to a fungi‐mediated organic‐N nutrient acquisition with shrub encroachment. Both ericoid shrub encroachment and higher mean annual temperature in the three sites triggered greater vascular plant biomass and consequently the dominance of decomposers (especially fungi), which led to a feeding community dominated by nematodes. This contributed to lower enzymatic multifunctionality. Our findings illustrate mechanisms by which plants influence ecosystem responses to climate change, through their effect on microbial trophic interactions.
Our findings illustrate mechanisms by which plants influence ecosystem responses to climate change, through their effect on microbial trophic interactions. The increase in ericaceous shrubs is marked by higher phenol concentration, DOC and TN in pore water. The ratio fungi to bacteria increases with the shift in vegetation, indicating a higher dependency on fungi‐mediated nutrient acquisition. Microbial community changes with a decrease in predator‐to‐prey mass ratio and a decrease in enzymatic multifunctionality.
Plant community modification may play an important role in peatlands’ carbon balance. We investigated how Molinia caerulea altered CO2 and CH4 fluxes and DOC concentration as well as their ...sensitivity to water table level, air and soil temperature in Sphagnum-dominated peat mesocosms. The presence of Molinia caerulea significantly increased CO2 and CH4 emissions compared to Sphagnum and decreased the DOC concentration. The rise in temperature exponentially increased DOC as well as CO2 and CH4 emissions. Molinia caerulea decreased the temperature sensitivity of CO2 emissions, suggesting the presence of a more labile substrate (root exudates), while it increased the temperature sensitivity of CH4 emissions, suggesting a possible change in methanogenic communities. Our study highlights a strong impact of vegetation change on C dynamics in peatlands.
•The occurrence of Molinia caerulea increases CO2 and CH4 emissions in Sphagnum-dominated peat mesocosms.•DOC concentration decreases with the presence of Molinia caerulea compared to Sphagnum with no Molinia caerulea.•CO2 and CH4 emissions and DOC concentration are strongly related to soil temperature.•Vegetation cover modifies the sensitivity of CO2 and CH4 emissions and DOC concentration to soil temperature.•Molinia caerulea could affect the composition of the methanogenic communities.
QUESTION: A better understanding of the response of Sphagnum mosses and associated vascular plants to climate warming is relevant for predicting the carbon balance of peatlands in a warmer world. ...Open‐top chambers (OTCs) have been used to investigate the effect on soil biogeochemical processes in peatlands, but little information is available on the effects of OTCs on microclimate conditions and the associated response of the plant community. We aimed to understand how simulated warming and differences in soil moisture affect plant species cover. LOCATION: A Sphagnum‐dominated peatlands in French Jura. METHODS: We used OTCs to measure the effect of a near‐ground temperature increase (+1.5 °C on average) on vegetation dynamics over five growing seasons (2008–2012) in a Sphagnum‐dominated peatland, in two adjacent microhabitats with different hydrological conditions – wet and dry. Microclimatic conditions and plant species abundance were monitored at peak biomass in years 1, 2, 3 and 5 and monthly during the plant growing season in year 5. RESULTS: The response to warming differed between vascular plants and bryophytes, as well as among species within these groups, and also varied in relation to soil moisture. Andromeda polifolia abundance responded positively to warming, while Vaccinium oxycoccus responded negatively, and Eriophorum vaginatum showed a high resistance. CONCLUSION: Depth of rooting of vascular plants appeared to control the response in plant abundance, while moss abundance depended on various other interacting factors, such as shading by the vascular plant community, precipitation and soil moisture.
The mechanisms behind the plant litter mixture effect on decomposition are still difficult to disentangle. To tackle this issue, we used a model that specifically addresses the role of the litter ...moisture content. Our model predicts that when two litters interact in terms of water flow, the difference of evaporation rate between two litters can trigger a nonadditive mixture effect on decomposition. Water flows from the wettest to the driest litter, changing the reaction rates without changing the overall litter water content. The reaction rate of the litter receiving the water increases relatively more than the decrease in the reaction rate of the litter supplying the water, leading to a synergistic effect. Such water flow can keep the microbial biomass of both litter in a water content domain suitable to maintain decomposition activity. When applied to experimental data (Sphagnum rubellum and Molinia caerulea litters), the model is able to assess whether any nonadditive effect originates from water content variation alone or whether other factors have to be taken into account.
The mechanisms behind the plant litter mixture effect on decomposition are still difficult to disentangle. The model proposed in this article predicts that when two litters interact in terms of water flow, the difference of evaporation rate between two litters can trigger a nonadditive mixture effect on decomposition. Water flows from the wettest to the driest litter, changing the reaction rates without changing the overall litter water content.
Mixotrophic protists are increasingly recognized for their significant contribution to carbon (C) cycling. As phototrophs they contribute to photosynthetic C fixation, whilst as predators of ...decomposers, they indirectly influence organic matter decomposition. Despite these direct and indirect effects on the C cycle, little is known about the responses of peatland mixotrophs to climate change and the potential consequences for the peatland C cycle. With a combination of field and microcosm experiments, we show that mixotrophs in the Sphagnum bryosphere play an important role in modulating peatland C cycle responses to experimental warming. We found that five years of consecutive summer warming with peaks of +2 to +8°C led to a 50% reduction in the biomass of the dominant mixotrophs, the mixotrophic testate amoebae (MTA). The biomass of other microbial groups (including decomposers) did not change, suggesting MTA to be particularly sensitive to temperature. In a microcosm experiment under controlled conditions, we then manipulated the abundance of MTA, and showed that the reported 50% reduction of MTA biomass in the field was linked to a significant reduction of net C uptake (-13%) of the entire Sphagnum bryosphere. Our findings suggest that reduced abundance of MTA with climate warming could lead to reduced peatland C fixation.
Nitrous oxide (N
O) is a powerful greenhouse gas and the main driver of stratospheric ozone depletion. Since soils are the largest source of N
O, predicting soil response to changes in climate or ...land use is central to understanding and managing N
O. Here we find that N
O flux can be predicted by models incorporating soil nitrate concentration (NO
), water content and temperature using a global field survey of N
O emissions and potential driving factors across a wide range of organic soils. N
O emissions increase with NO
and follow a bell-shaped distribution with water content. Combining the two functions explains 72% of N
O emission from all organic soils. Above 5 mg NO
-N kg
, either draining wet soils or irrigating well-drained soils increases N
O emission by orders of magnitude. As soil temperature together with NO
explains 69% of N
O emission, tropical wetlands should be a priority for N
O management.
Hydrological disturbances could increase dissolved organic carbon (DOC)
exports through changes in runoff and leaching, which reduces the potential
carbon sink function of peatlands. The objective of ...this study was to assess
the impact of hydrological restoration on hydrological processes and DOC
dynamics in a rehabilitated Sphagnum-dominated peatland. A
conceptual hydrological model calibrated on the water table and coupled with
a biogeochemical module was applied to La Guette peatland (France), which
experienced a rewetting initiative on February 2014. The model (eight
calibrated parameters) reproduced water-table (0.1<NS<0.61) and pore-water DOC concentrations (2<RMSE<11 mg L−1) in a time series (1 April 2014 to
15 December 2017) in two contrasting locations (rewetted and control) in the
peatland. Hydrological restoration was found to impact the water balance
through a decrease in slow deep drainage and an increase in fast superficial
runoff. Observed DOC concentrations were higher in summer in the rewetted
location compared to the control area and were linked to a difference in
dissolved organic matter composition analyzed by fluorescence. Hydrological conditions,
especially the severity of the water-table drawdown in summer, were
identified as the major factor controlling DOC-concentration dynamics. The
results of the simulation suggest that the hydrological restoration did not
affect DOC loads, at least in a short-term period (3 years). However, it
impacted the temporal dynamics of DOC exports, which were the most episodic
and were mainly transported through fast surface runoff in the area affected
by the restoration, while slow deep drainage dominated DOC exports in the
control area. In relation to dominant hydrological processes, exported DOC is
expected to be derived from more recent organic matter in the top peat layer
in the rewetted area, compared to the control area. Since it is calibrated on
water-table and DOC concentration, the model presented in this study proved
to be a relevant tool in identifying the main hydrological processes and
factors controlling DOC dynamics in different areas of the same peatland. It
is also a suitable alternative to a discharge-calibrated catchment model when
the outlet is not easy to identify or to monitor.
Soil microbial communities are vital for multiple ecosystem processes and services. In particular, soil microbial food webs are key determinants of soil biodiversity, functioning and stability. ...Unclear, however, is how structural features of food webs, such as species richness and turnover, biomass and energy transfer across trophic levels, influence the provisioning and stability of ecosystem functioning. Here, we explore the relationships between different facets of microbial food web structure (e.g. species richness, connectance, biomass and energy fluxes across trophic levels) and ecosystem functions (i.e. decomposition and microbial enzyme activity) across different habitats and depths in a peatland. We show that no aspect of taxonomic richness directly explained variation in ecosystem functions. Instead, we find that trophic interactions between basal species and primary consumers, and especially increasing connectance, biomass and energy flux transiting from decomposers and phototrophs to algivores, bacterivores and fungivores, enhance ecosystem functions in the peatland. These findings demonstrate that focusing on taxonomic diversity without explicit inclusion of food web structure and energy flows therein gives an incomplete and uninformative comprehension of relationships between biodiversity and ecosystem functioning, at least in peatlands. Our findings further suggest that the inclusion of soil microbial food webs in large-scale biogeochemical models is of fundamental importance to provide the necessary guidance for managing and mitigating the effects of environmental change.
•Soil microbial food webs determine soil biodiversity and ecosystem functioning.•What aspect of microbial food web underpin ecosystem functions is unclear.•Biomass and energy flux dynamics, but not taxonomic richness, influence peatland ecosystem functions.•The inclusion of microbial food web properties in biogeochemical models is fundamental.
The present study was aimed at examining the distribution and abundance of glycerol dialkyl glycerol tetraethers (GDGTs) of archaeal and bacterial origin in peat samples from surface and deep (ca. 50
...cm) horizons of a peat bog in the Jura Mountains (northeastern France). Two principal types of GDGTs are present: extractable GDGTs, recoverable using solvent extraction, and non-extractable GDGTs, linked to the soil matrix. Within the extractable pool, “free” (i.e. core lipids) and “bound” (i.e. intact polar and/or ester-bound lipids) GDGTs can be distinguished. Extractable “free” and “bound” GDGTs were extracted using both accelerated solvent extraction (ASE) and a modified Bligh and Dyer technique. Both methods were shown to allow adequate extraction of “free” archaeal and bacterial GDGTs from soil samples. Both extraction protocols afforded similar relative distributions of archaeal and bacterial GDGTs, although poorer extraction of “bound” GDGTs was observed for ASE relative to Bligh and Dyer. Even though only low amounts of bacterial GDGTs were released after acid hydrolysis of solvent-extracted samples, non-extractable and total extractable GDGTs showed different distribution patterns in some samples. Consequently, these two lipid pools potentially reflect different proxy records of mean annual air temperature (MAAT) and pH. Last, the distribution of bacterial GDGTs differed between the different samples. Samples from deep horizons gave lower GDGT-derived MAAT values than those from surficial horizons, in agreement with measured soil temperatures at 7
cm and 50
cm depths from April to September. MAAT estimates more closely resemble spring and summer temperatures than annual soil temperature. The variability in bacterial GDGT distribution and resulting MAAT estimates probably also reflects the heterogeneity of peat samples and the variation in several environmental factors such as peat moisture level and oxygen availability.
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