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Glob Chang Biol. 2018 Mar;24(3):972-986. doi: 10.1111/gcb.13928. Epub 2017 Nov 6.

Tipping point in plant-fungal interactions under severe drought causes abrupt rise in peatland ecosystem respiration.

Author information

1
Functional Ecology and Environment laboratory, University of Toulouse, CNRS, INP, UPS, Toulouse Cedex, France.
2
Ecological Systems Laboratory (ECOS), School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
3
WSL-Swiss Federal Institute for Forest, Snow and Landscape Research, Site Lausanne, Lausanne, Switzerland.
4
Laboratory of Wetland Ecology and Monitoring & Department of Biogeography and Palaeoecology, Adam Mickiewicz University, Poznań, Poland.
5
Department of Geoecology and Climatology, Institute of Geography and Spatial Organization, Polish Academy of Sciences, Warsaw, Poland.
6
Biological Sciences, University of Southampton, Southampton, UK.
7
Laboratory of Soil Biodiversity, University of Neuchâtel, Neuchâtel, Switzerland.
8
Arctic and Marine Biology Department, University of Tromsø, Tromsø, Norway.
9
Real Jardín Botánico, CSIC, Madrid, Spain.
10
Department of Environmental Resources and Geohazards, Institute of Geography and Spatial Organization, Polish Academy of Sciences, Warszawa, Poland.
11
Department of Life Science and Biotechnologies, University of Ferrara, Ferrara, Italy.
12
Meteorology Department, Poznan University of Life Sciences, Poznań, Poland.
13
Botanical Garden of Neuchâtel, Neuchâtel, Switzerland.

Abstract

Ecosystems are increasingly prone to climate extremes, such as drought, with long-lasting effects on both plant and soil communities and, subsequently, on carbon (C) cycling. However, recent studies underlined the strong variability in ecosystem's response to droughts, raising the issue of nonlinear responses in plant and soil communities. The conundrum is what causes ecosystems to shift in response to drought. Here, we investigated the response of plant and soil fungi to drought of different intensities using a water table gradient in peatlands-a major C sink ecosystem. Using moving window structural equation models, we show that substantial changes in ecosystem respiration, plant and soil fungal communities occurred when the water level fell below a tipping point of -24 cm. As a corollary, ecosystem respiration was the greatest when graminoids and saprotrophic fungi became prevalent as a response to the extreme drought. Graminoids indirectly influenced fungal functional composition and soil enzyme activities through their direct effect on dissolved organic matter quality, while saprotrophic fungi directly influenced soil enzyme activities. In turn, increasing enzyme activities promoted ecosystem respiration. We show that functional transitions in ecosystem respiration critically depend on the degree of response of graminoids and saprotrophic fungi to drought. Our results represent a major advance in understanding the nonlinear nature of ecosystem properties to drought and pave the way towards a truly mechanistic understanding of the effects of drought on ecosystem processes.

KEYWORDS:

biodiversity-ecosystem functioning; ecosystem shifts; fungal diversity; hydrolases; moving window structural equation model; oxidases; plant-soil feedbacks; threshold

PMID:
28991408
DOI:
10.1111/gcb.13928

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