Abstract
Abstract
Soil extracellular enzymes are produced and excreted by soil microbial organisms. They catalyze many of the biochemical reactions that support crucial ecosystem functions like decomposition, organic matter mineralization, nutrient cycling, and C sequestration. Microbial communities that produce these enzymes are shaped in part by plant diversity and composition, but the relationships between plant communities and enzyme activities are not well resolved. Diverse plant communities may provide a diversity of soil organic matter inputs that support high microbial diversity and function. This would predict positive relationships between enzyme activities and plant diversity, particularly plant functional trait diversity that more closely reflects the diversity of soil inputs. Alternatively, dominant plant functional groups may shape microbial communities and activities, such as legumes that add N‐rich resources to soil. These impacts might be seen in microbes by the relative acquisition of different resources, such as the activity ratio of C‐acquiring β‐glucosidase and N‐acquiring N‐acetyl‐β‐D‐glucosaminidase. We use soil enzyme and plant community data from four separate grassland studies—two experiments and two observational community studies—to ask how plant diversity and functional composition affect enzyme activities. There were relationships between enzyme activities and plants for the observational community studies, but not the experimental studies, so plant–soil enzyme relationships may take time to emerge. At one community site, activities for four hydrolytic enzymes declined with plant Shannon diversity, and β‐glucosidase activity increased with greater functional trait diversity. The ratio of C‐acquiring β‐glucosidase and N‐acquiring N‐acetyl‐β‐D‐glucosaminidase activities increased with plant diversity and cover of nitrogen‐fixers, or declined with graminoid cover, suggesting that microbes reduced their relative allocation of resources to N acquisition when plant inputs made N more accessible. If lower activities of enzymes targeting C‐rich compounds are indicators of higher potential for C sequestration, then grassland plant communities with high taxonomic diversity may promote C storage. This could provide strong justification for management and restoration strategies that sustain high plant biodiversity. However, the inconsistent results, with enzyme activity unrelated to plants in both experimental studies, imply that other environmental factors correlated with plant composition may be stronger determinants of soil enzymes in some grassland settings.