Extracellular enzyme stoichiometry reflects the metabolic C-and P-limitations along a grassland succession on the Loess Plateau in China.

Soil extracellular enzyme stoichiometry (EES) reflects the biogeochemical balance between microbial metabolic requirements and environmental nutrient availability. Recent research suggests that EES well effect on soil microbial metabolic limitations (SMMLs), however, few field studies have explicitly tested this based on a herbaceous successional chronosequence. We used the EES models to identify the response of SMMLs, and investigated the potential implications of microbial nutritional limitations across the time series (herbaceous succession) and space (transformation interface soil [TIS] and underlying topsoil [UTS] layer) in the grassland restoration series. We show that soil microorganisms were generally limited by C, both in the TIS and UTS. Microbial C-limitation exhibited a unimodal direction, peaking in intermediate successional stages, however, P-limitation presented the opposite trend. During herbaceous succession, microbial P-limitation was more substantial than that in N-limitation. SMMLs gradually transferred from P- to N- and back to P-limitation at later successional stages in the TIS layer. Furthermore, we demonstrate that biotic factors, soil basic index, and soil nutrients explained 92.2 % of the variations in microbial C-limitation and 84.4 % of the variations in microbial P-limitation. Multi–interaction factors exhibited the most significant relative influences of 65.11 % (TIS) and 43 % (UTS) on the SMMLs. Microbial C-limitation was induced by the imbalance between C supply and microbial C demand, whereas the changes in microbial P-limitation were due to the changes in the competition for P between plants and microorganisms. Overall, our findings provide support for microbial C- and P-limitation in the process of herbaceous succession during the restoration. We also highlight the possibility of additive effects on soil SMMLs via interactions of vegetation composition, soil properties, and microbial nutritional demands, which might constrain soil microbial metabolism requirements despite greater living root and litter resource inputs.