Continental-scale drivers of soil microbial extracellular polymeric substances

Extracellular polymeric substances (EPS) are key microbial residues that contribute to soil organic carbon (SOC) and promote soil aggregation. Yet, their abundance and large-scale controls have only begun to be investigated. We conduct extensive soil sampling across a European transect spanning diverse climates, bedrocks, and land uses. Average soil EPS content is 956 ± 55 µg g^-1 soil (n= 92 sites), with EPS-carbon (EPS-C) contributing 1.6 ± 0.1% to SOC. Bedrock influences EPS content, EPS-C contribution to SOC, and the EPS-C/microbial biomass carbon (MBC) ratio, whereas land use mainly affects the latter two. The EPS-C/MBC ratio is negatively correlated with microbial growth and carbon use efficiency, and increases under water deficit, while EPS increases with MBC, clay content, and exchangeable calcium. Our results demonstrate that EPS represents a functionally important microbial residue, regulated by climatic, edaphic, microbial, and land-use factors, with significant implications for soil carbon cycling and sequestration.