PNNL

Abstract

Soil microbes ultimately drive the mineralization of soil organic carbon, and thus the heterotrophic respiration. We compiled a dataset of the seasonality of microbial biomass carbon (MBC) across the northern hemisphere (no measurements were available from the southern hemisphere) and developed a semi-mechanistic model to map the monthly MBC across the globe. MBC exhibits an equatorially symmetric seasonality between the northern and southern hemispheres. In the northern hemisphere, MBC peaks in fall and is minimal in spring at low latitudes (0-25° N); peaks in spring and is minimal in autumn at mid-latitudes (25°-50° N); and peaks in summer and is lowest in winter at high latitudes (>50° N). This MBC seasonality along latitude can be attributed to an interactive impacts of soil temperature, soil moisture and substrate. The MBC seasonality is inconsistent with that of heterotrophic respiration, indicating the MBC as a proxy for microbial activity is inappropriate at this timescale. This study highlights the need to explicitly represent microbial physiology into microbial models and the necessity for more spatially- and temporally-representative sampling campaigns measuring MBC globally.