Hysteretic temperature sensitivity of wetland CH4 fluxes explained by substrate availability and microbial activity

Kuang-Yu Chang1, William J. Riley1, Patrick M. Crill2, Robert F. Grant3, and Scott R. Saleska4

1Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
2Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
3Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada
4Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, USA

https://doi.org/10.5194/bg-17-5849-2020

Abstract
Methane (CH4) emissions from wetlands are likely increasing and important in global climate change assessments. However, contemporary terrestrial biogeochemical model predictions of CH4 emissions are very uncertain, at least in part due to prescribed temperature sensitivity of CH4 production and emission. While statistically consistent apparent CH4 emission temperature dependencies have been inferred from meta-analyses across microbial to ecosystem scales, year-round ecosystem-scale observations have contradicted that finding. Here, we show that apparent CH4 emission temperature dependencies inferred from year-round chamber measurements exhibit substantial intra-seasonal variability, suggesting that using static temperature relations to predict CH4 emissions is mechanistically flawed. Our model results indicate that such intra-seasonal variability is driven by substrate-mediated microbial and abiotic interactions: seasonal cycles in substrate availability favors CH4 production later in the season, leading to hysteretic temperature sensitivity of CH4 production and emission. Our findings demonstrate the uncertainty of inferring CH4 emission or production rates from temperature alone and highlight the need to represent microbial and abiotic interactions in wetland biogeochemical models.