Extracellular polymeric substances are closely related to land cover, microbial communities, and enzyme activity in tropical soils

Extracellular polymeric substances (EPS) form the main matrix of microbial biofilms and play a crucial role in maintaining microbial life. However, factors influencing EPS concentration and production in soil are poorly understood. Here we show that EPS are closely related to microbial communities and nutrient acquisition in tropical forest and cropland soils with varying iron-aluminum-manganese concentrations and total reserve in base cations. We found under homogenized moisture and temperature conditions that EPS concentration and production efficiency (i.e., EPS per unit of microbial biomass) depend more on land cover than on geochemical soil properties. EPS concentration and production efficiency were higher in cropland than in forest soil and were related to the higher relative abundance of microbial sequences identified as Paenibacillaceae, Ramlibacter, Chaetosphaeria, Burkholderiaceae, and Xanthobacteraceae, pointing to potential EPS producers. In contrast, lower EPS concentration in forest soil was related to the higher relative abundance of microbial sequences associated with e.g., Gemmatimonas and Massilia, suggesting potential EPS degradation. We also found that EPS production efficiency was positively related to microbial investment in nutrient acquisition, implying that EPS production likely follows the same principles as extracellular enzyme activity. That is, EPS production may increase when resources are scarce to facilitate nutrient acquisition, and decrease when resources are abundant. Overall, microbial community composition and resource demand seem to control EPS degradation and accumulation in tropical soils, which could influence microbially-driven carbon and nutrient cycling.