The 5th International Conference of Geobiology

Anthropogenic climate change will affect a wide range of environmental conditions, including precipitation and soil moisture content. However, its impact on key biogeochemical processes and associated feedback mechanisms as well as the potential existence of critical thresholds is poorly constrained. Here we use flux, lipid and genomic data along several natural grassland transects in NW China to assess the impact of changes in soil moisture content on methane cycling in grassland soils, an ecosystem that plays a crucial role in regulating the concentration of this potent greenhouse gas. We show that these soils abruptly switch from being a methane source to sink caused by a minor change in soil moisture content around a threshold, which is driven by a sudden replacement of the archaeal methanogen community by methanotrophic bacteria. Combined with our climate simulations that indicate widespread grasslands drying during the 21^st century under anthropogenic climate change scenarios, our results highlight the existence of an abrupt feedback mechanism that has the potential to alter the methane cycle during this century by significantly reducing the emissions of methane from grasslands to the atmosphere. Our results hold implications for carbon emissions targets and should be incorporated into projections of future emissions.

climate change,methane cycle,soil moisture,microbial ecology,biogeochemistry