November 20, 2020

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Hysteretic Temperature Sensitivity of Wetland CH4 Fluxes Explained by Substrate Availability and Microbial Activity

The Science

Wetland methane (CH4) emissions are likely increasing and important in global climate change assessments; however, the temperature sensitivity of CH4 production and emission remains very uncertain. Here reseachers from NGEE-Arctic use a well-tested mechanistic ecosystem model to examine the observed apparent CH4 emission hysteresis to air and soil temperatures. Their simulations indicate that these hysteretic relationships are driven by substrate-mediated microbial and abiotic interactions: seasonal cycles in substrate availability favors CH4 production later in the season, leading to higher CH4 production and emission rates at the same temperature.

The Impact

The experimental simulations show substantial intra-seasonal variability in the temperature sensitivity of CH4 production and emission. These findings demonstrate the uncertainty of inferring CH4 production or emission rates from temperature alone and highlight the need to properly represent microbial and abiotic interactions in terrestrial biogeochemical models.

Summary

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, researchers from NGEE-Arctic 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. The model results indicate that this 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. These findings demonstrate the uncertainty of inferring CH4emission or production rates from temperature alone and highlight the need to represent microbial and abiotic interactions in wetland biogeochemical models.

Principal Investigator

William Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This study was funded by the Genomic Science Program of the United States Department of Energy Office of Biological and Environmental Research under the ISOGENIE (DE-SC0016440) and NGEE-Arctic projects under contract DE- AC02-05CH11231 to Lawrence Berkeley National Laboratory.

References

Chang, K.-Y., W. J. Riley, P. M. Crill, R. F. Grant, and S. R. Saleska. "Hysteretic temperature sensitivity of wetland CH4 fluxes explained by substrate availability and microbial activity". Biogeosciences 17 5849–860  (2020). https://doi.org/10.5194/bg-17-5849-2020.