Soil extracellular enzyme stoichiometry reflects the shift from P- to N-limitation of microorganisms with grassland restoration

Abstract Soil extracellular enzyme stoichiometry (EES), the ratio of extracellular enzyme activities (EEAs) related to the acquisition of nutrients such as carbon (C), nitrogen (N) and phosphorus (P), reflects the demand for resources by microorganisms. However, how grassland restoration shifts microbial nutrient limitation as indicated by soil EES remains unclear. Here, we evaluated microbial nutrient limitation by studying soil EES across a chronosequence of grassland restoration sites. The ratio of the natural logarithm of C-, N-, and P-acquiring enzymes in our studied system ranged from 1:1.47:1.05 to 1:0.82:1.38, and the average was 1:1.08:1.28, deviating from the global ratio of 1:1:1 and indicating that microorganisms were co-limited by N and P. Enzyme N:P ratio increased and vector angles decreased with time since restoration, suggesting that the restored grassland shifted from P-limitation (angles>45°) to N-limitation (angles