Above- and belowground linkages in Sphagnum peatland: climate warming affects plant-microbial interactions

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

Assessing the responses of Sphagnum micro-eukaryotes to climate changes using high throughput sequencing

Alexandre Buttler, Vincent Eric Jules Jassey, Mariusz Lamentowicz, Enrique Lara, Edward Mitchell

Current projections suggest that climate warming will be accompanied by more frequent and severe drought events. Peatlands store ca. one third of the world's soil organic carbon. Warming and drought may cause peatlands to become carbon sources through stimulation of microbial activity increasing ecosystem respiration, with positive feedback effect on global warming. Micro-eukaryotes play a key role in the carbon cycle through food web interactions and therefore, alterations in their community structure and diversity may affect ecosystem functioning and could reflect these changes. We assessed the diversity and community composition of Sphagnum-associated eukaryotic microorganisms inhabiting peatlands and their response to experimental drought and warming using high throughput sequencing of environmental DNA. Under drier conditions, micro-eukaryotic diversity decreased, the relative abundance of autotrophs increased and that of osmotrophs (including Fungi and Peronosporomycetes) decreased. Furthermore, we identified climate change indicators that could be used as early indicators of change in peatland microbial communities and ecosystem functioning. The changes we observed indicate a shift towards a more "terrestrial'' community in response to drought, in line with observed changes in the functioning of the ecosystem.

PEERJ INC2020

Seasonal patterns of testate amoeba diversity, community structure and species-environment relationships in four Sphagnum-dominated peatlands along a 1300 m altitudinal gradient in Switzerland

Luca Bragazza, Alexandre Buttler, Vincent Eric Jules Jassey, Mariusz Lamentowicz, Edward Mitchell

Altitudinal gradients are useful to study the potential effects of climate change on ecosystems. Historically, studies on elevation gradients have primarily focused on macro-organisms and ecosystem processes, while microorganisms have been mostly ignored despite their ubiquity and functional importance. We studied the temporal (about every two months from June 2008 until May 2009) variation of testate amoeba communities in four Sphagnum-dominated peatlands along a 1300 to elevation gradient in the Swiss Mountains (580-1880 m) in relation to water table depth and hydrochemistry with special focus on dissolved organic carbon (DOC), a useful proxy for changes in C-cycling in peatlands. The lowest site had significantly (P < 0.01) lowest testate amoeba density, species richness. The highest site had highest testate amoeba density (38 ind mg(-1) dry mass of Sphagnum). Seasonal fluctuations in testate amoeba species richness and diversity were not consistent among sites but density tended to peak in spring at all sites, autumn in the three highest sites and mid-winter in the upper two sites. In a redundancy analysis (RDA) community structure was more strongly correlated to altitude (33.8% of variance explained in living community) than to soil hydrological and hydro-chemical variables (together explaining 16.2% of variance). In a partial RDA with altitude used as covariable, the four sites were separated by DOP, DOC, DON, pH and average depth to water table. The abundance of high trophic level testate amoeba species (shell-aperture over their body size >0.20; i.e. primarily predators of protists and micro-metazoa) as well as the community size structure increased from lowest to highest elevation (respectively by 3.7x and 6x) and followed the seasonal patterns of total density, while DOC, DON, and DOC/DON decreased with elevation. These results agree with previously reported alteration of peatland microbial food chains in response to experimental warming, suggesting that climate-induced changes in microbial community structure (here a shortening of microbial food chains) represent a mechanism controlling the carbon balance of peatlands. (C) 2013 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2013

Alternative Scenarios for the Development of Oil Palm in the Tropics: Carbon and Nutrients Dynamics

Juan Carlos Quezada Rivera

Expansion of agriculture in forested areas poses significant threats and pressure to ecosystems and potentially the global climate. More specifically, expansion of oil palm (OP) plantations has been found to exert great impact on key ecosystem functions like C storage, water cycling and support biodiversity. Alternative pathways for a more sustainable development of agriculture have been proposed. However, lack of evidence through comprehensive studies constrains the potential of deforestation free options to be accounted as a fundamental part or as priority scenarios of future sustainable OP development. This thesis work looks to provide insights into the effects of two alternatives land use change options into OP: planted pastures and savanna conversion on soil biogeochemical aspects and ecosystem C storage. Pastures conversion into OP was C neutral at the ecosystem level (Manuscript 1), however soil C storage decreased by 39% during the first OP cycle, ca. 30 years, and then remained stable along the second OP cycle. This ecosystem C neutrality contrasts remarkably with the deforestation scenario for OP development, where about 173 Mg C ha-1 are lost due to the establishment of OP plantations. Another positive implication of establishing OP in pasture areas was the increased chemical fertility. However, this trade-off between soil C storage and chemical fertility demands close attention so that soil fertility could be enhanced mainly by means of soil natural processes rather than by adding chemical inputs. Such reliability on SOC to enhance soil fertility in OP plantations is possible in the long-term as indicated by the found recovery of labile C fractions and bulk soil C content in the topsoil (Manuscript 4). In the conversion of savannas into OP plantations, a rather positive ecosystem C balance was found (Manuscript 2). Such C gain at the ecosystem level was mainly explained by the no change in soil C stocks over an entire OP rotation cycle, which in turn was due to the slow decomposition of savanna-derived C and effective OP-derived C accumulation that offset the small savanna C losses. Importantly, soil biological activity and SOC stocks were found to be maintained or even enhanced, when organic amendments (i.e. crop residues from frond piles) were used. This contrasted, with the practice that relied heavily on mineral fertilizers application to increase chemical fertility. It was also demonstrated that changes in SOC stocks within plantations are mainly driven by C inputs that are controlled by OP fine roots (Manuscript 3). The fine OP roots were directly affected by nutrients addition and drive changes in soil microbial properties. This work demonstrates that alternatives LUC to OP can reduce significantly the C losses associated with deforestation. Future OP development should be directed toward degraded pastures areas so that the initial SOC losses are not as high as found in the well-managed pastures of this work. Notably, the management decisions will play a key role on the direction and strength of SOC stock changes and can further increase the positive ecosystem C outcomes and soil C storage capacity of OP plantations in former savanna or pasture areas. Therefore, OP cultivation should shift toward a more ecologically oriented intensification with a better balance between environmental and productivity goals.