Divergent regulating modes of greenhouse gas emissions at different soil layers under altered precipitation regime

Abstract

How soil microbial communities regulate greenhouse gas (GHG) emissions as precipitation events are “repackaged” from many small events to a few larger events has received significant attention. Previous studies have quantified the net fluxes of GHG across the soil/atmosphere interface; however, they have not investigated GHG fluxes in soil profiles under altered precipitation regimes. This study investigated the joint regulation of topsoil and subsoil microorganisms on GHG emissions under changes in precipitation regime in an alpine meadow. Severely altered precipitation regimes have led to changes in NO3–, DOC, and soil moisture among different soil layers, which can be attributed to a combination of substrate migration and changes in carbon and nitrogen mineralization rates. Topsoil microorganisms exhibit high sensitivity to severe changes in the precipitation regime, which can affect their biomass, microbial composition, and metabolic activities. In contrast, the activity of subsoil microorganisms remains relatively stable. This was likely due to the heterogeneity of dominant regulators across soil layers. Under the severely altered precipitation regime, carbon dioxide (CO2) emissions significantly decreased by approximately 11.08%. This decrease was primarily due to a reduction in microbial respiration in the topsoil. The decrease in both topsoil and subsoil methane (CH4) uptake likely caused the inhibition of the CH4 sink from the surface (by approximately 11.60%). While a 1.75-fold increase in nitrous oxide (N2O) emissions under the severe changes in the precipitation regime might be primarily related to the increase in subsoil N2O emissions caused by the increasing abundance of subsoil denitrifiers, as well as the addition of subsoil nitrate content and soil moisture. This study revealed the divergent modes of microbial communities at different soil layers regulating GHG fluxes, which could guide the improvement of ecological models predicting GHG emissions in response to altered precipitation regimes.