Predator-prey mass ratio drives microbial activity under dry conditions in Sphagnum peatlands

Monika K Reczuga (1, 2, 3) , Mariusz Lamentowicz (1, 2) , Matthieu Mulot (4) , Edward a D Mitchell (4, 5) , Alexandre Buttler (1, 6, 7, 8, 9) , Bogdan Chojnicki (10) , Michał Słowiński (11) , Philippe Binet (8, 9) , Geneviève Chiapusio (12, 8, 9) , Daniel Gilbert (8, 9) , Sandra Słowińska (11) , Vincent E J Jassey (6, 13, 14, 9)

1 Laboratory of Wetland Ecology and Monitoring, Faculty of Geographical and Geological Sciences
2 Department of Biogeography and Palaeontology, Faculty of Geographical and Geological Sciences
3 Faculty of Biology
4 Laboratory of Soil Biodiversity
5 Jardin Botanique de Neuchâtel
6 Swiss Federal Research Institute
7 Laboratory of System Ecology, School of Architecture, Civil and Environmental Engineering
8 LCE - Laboratoire Chrono-environnement (UMR 6249)
9 CNRS - Centre National de la Recherche Scientifique
10 Faculty of Environment Engineering and Spatial Management, Department of Meteorology
11 Department of Geoecology and Climatology, Institute of Geography and Spatial Organization
12 CARRTEL - Centre Alpin de Recherche sur les Réseaux Trophiques et Ecosystèmes Limniques
13 Laboratory of System Ecology School Architecture Civil and Environment Engineering
14 LEFE - Laboratoire Ecologie Fonctionnelle et Environnement

Mid- to high-latitude peatlands are a major terrestrial carbon stock but become carbon sources during droughts, which are increasingly frequent as a result of climate warming. A critical question within this context is the sensitivity to drought of peatland microbial food webs. Microbiota drive key ecological and biogeochemical processes, but their response to drought is likely to impact these processes. Peatland food webs have, however, been little studied, especially the response of microbial predators. We studied the response of microbial predators (testate amoebae, ciliates, rotifers, and nematodes) living in Sphagnum moss carpet to droughts, and their influence on lower trophic levels and on related microbial enzyme activity. We assessed the impact of reduced water availability on microbial predators in two peatlands using experimental (Linje mire, Poland) and natural (Forbonnet mire, France) water level gradients, reflecting a sudden change in moisture regime (Linje), and a typically drier environment (Forbonnet). The sensitivity of different microbial groups to drought was size dependent; large sized microbiota such as testate amoebae declined most under dry conditions (-41% in Forbonnet and -80% in Linje). These shifts caused a decrease in the predator-prey mass ratio (PPMR). We related microbial enzymatic activity to PPMR; we found that a decrease in PPMR can have divergent effects on microbial enzymatic activity. In a community adapted to drier conditions, decreasing PPMR stimulated microbial enzyme activity, while in extreme drought experiment, it reduced microbial activity. These results suggest that microbial enzymatic activity resulting from food web structure is optimal only within a certain range of PPMR, and that different trophic mechanisms are involved in the response of peatlands to droughts. Our findings confirm the importance of large microbial consumers living at the surface of peatlands on the functioning of peatlands, and illustrate their value as early warning indicators of change.

Mots clés: poor fen; protists; soil moisture; Wetlands; body size; drought; food web; phenoloxidase; water table manipulation; microbial activity; peatlands

Mots clés: phénoloxydase; protiste; activité microbienne; sécheresse; tourbière

Domaines: Biodiversité et Ecologie

Monika K Reczuga, Mariusz Lamentowicz, Matthieu Mulot, Edward a D Mitchell, Alexandre Buttler, et al.. Predator-prey mass ratio drives microbial activity under dry conditions in Sphagnum peatlands. Ecology and Evolution, 2018, 8 (11), pp.5752-5764. ⟨10.1002/ece3.4114⟩. ⟨hal-01833617⟩