Identifying environmental drivers of greenhouse gas emissions under warming and reduced rainfall in boreal-temperate forests

Authors: MARTINS, CATARINA SC - Western Sydney University; NAZARIES, LOIC - Western Sydney University; DELGADO-BAQUERIZO, MANUEL - Western Sydney University; MACDONALD, CATRIONA - Western Sydney University; ANDERSON, IAN - Western Sydney University; HOBBIE, SARAH - University Of Minnesota; Venterea, Rodney - Rod; REICH, PETER - University Of Minnesota; SINGH, BRAJESH - Western Sydney University

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2017
Publication Date: 6/22/2017
Citation: Martins, C., Nazaries, L., Delgado-Baquerizo, M., Macdonald, C.A., Anderson, I.C., Hobbie, S.E., Venterea, R.T., Reich, P.B., Singh, B.K. 2017. Identifying environmental drivers of greenhouse gas emissions under warming and reduced rainfall in boreal-temperate forests. Functional Ecology. 31:2356-2368. doi:10.1111/1365-2435.12928.
DOI: https://doi.org/10.1111/1365-2435.12928

Interpretive Summary: Atmospheric concentrations of the important greenhouse gases (GHG) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are predicted to increase as a consequence of fossil fuel emissions. Forest ecosystems in general and forest soils in particular can be sinks or sources for CO2, CH4, and N2O. Environmental studies traditionally target soil temperature and moisture as the main predictors of soil GHG flux from different ecosystems; however, these emissions are primarily biologically driven. Thus, little is known about the degree of regulation of biotic vs. abiotic factors on GHG emissions, particularly under future climate predictions of increasing global temperatures and changes in intensity and frequency of precipitation events. Here we measured CO2, CH4 and N2O fluxes after 5 years of experimental warming (+3.4°C), and 2 years of ˜45% summer rainfall reduction, in two forest sites in a boreal-temperate ecotone, under different habitat conditions (canopy present and absent), in Minnesota, USA; and evaluated the importance of such climo-edaphic drivers (soil texture, canopy, seasonality, climate and soil physicochemical properties) and microbial abundances on GHG emissions. We found that changes in CO2 fluxes were mainly abiotically driven by soil temperature and moisture. Methane fluxes were both abiotic and microbially influenced, by gas diffusivity (via soil texture) and methanotroph pmoA gene abundance, respectively. Similarly, N2O emissions showed a strong biotic regulation (via ammonia-oxidizing bacteria amoA gene abundance). Warming did not significantly alter CO2 and CH4 fluxes after 5 years of manipulation, whereas N2O emissions were higher under warmed conditions under open canopy conditions. Our findings provide evidence of direct and indirect effects of both biotic and abiotic soil characteristics on soil GHG emissions. Overall, this study highlights the need to include both microbial and climo-edaphic properties in predictive models in order to provide a better mechanistic understanding for the development of future mitigation strategies. Improved models will assist scientists and policy makers in their ability to predict and manage impacts of climate change on soil biochemical responses including GHG emissions.

Technical Abstract: Atmospheric concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are predicted to increase as a consequence of fossil fuel emissions and biosphere-atmosphere interactions. Forest ecosystems in general and forest soils in particular can be sinks or sources for CO2, CH4, and N2O. Environmental studies traditionally target soil temperature and moisture as the main predictors of soil greenhouse gas (GHG) flux from different ecosystems; however, these emissions are primarily biologically driven. Thus, little is known about the degree of regulation of biotic vs. abiotic factors on GHG emissions, particularly under future climate predictions of increasing global temperatures and changes in intensity and frequency of precipitation events. Here we measured CO2, CH4 and N2O fluxes after 5 years of experimental warming (+3.4°C), and 2 years of ˜45% summer rainfall reduction, in two forest sites in a boreal-temperate ecotone, under different habitat conditions (canopy present and absent), in Minnesota, USA; and evaluated the importance of such climo-edaphic drivers (soil texture, canopy, seasonality, climate and soil physicochemical properties) and microbial abundances on GHG emissions. We found that changes in CO2 fluxes were mainly abiotically driven by soil temperature and moisture. Methane fluxes were both abiotic and microbially influenced, by gas diffusivity (via soil texture) and methanotroph pmoA gene abundance, respectively. Similarly, N2O emissions showed a strong biotic regulation (via ammonia-oxidizing bacteria amoA gene abundance). Warming did not significantly alter CO2 and CH4 fluxes after 5 years of manipulation, whereas N2O emissions were higher under warmed conditions under open canopy conditions. Our findings provide evidence of direct and indirect effects of both biotic and abiotic soil characteristics on soil GHG emissions. Overall, this study highlights the need to include both microbial and climo-edaphic properties in predictive models in order to provide a better mechanistic understanding for the development of future mitigation strategies.