Ecoenzymatic stoichiometry and microbial nutrient limitation during secondary succession of natural grassland on the Loess Plateau, China

Soil microbial metabolism is vital for nutrient cycling and ecosystem stability. To quantify microbial metabolism and nutrient limitation during plant secondary succession, we measured soil physicochemical properties, microbial biomass, and four enzyme activities (beta-1,4-glucosidase (BG), beta-1,4-N-acetylglucosaminidase (NAG), L-leucine aminopeptidase (LAP), and alkaline phosphatase (AP)) and identified the changes of soil ecoenzymatic stoichiometry and microbial nutrient limitation along a secondary succession series in typical arid and semi-arid ecosystems on the Loess Plateau, China. Soil enzyme activities increased in the first 17a succession and then decreased with plant secondary succession. The ln(BG):ln(NAG+ LAP) ratio and ln(BG):ln(AP) ratio showed a decreasing trend in the first 22a succession and then increased. Most soil nutrient contents and nutrient stoichiometry were significantly correlated with enzyme activities and enzymatic stoichiometry. Moreover, vector analysis of soil enzymes indicated that microbial community were co-limited by C and P during secondary succession. Linear regression of C:N and C:P between the soil nutrient and microbial community showed that soil microbial community maintained stoichiometry homeostasis during plant secondary succession. The threshold elemental ratio revealed that the microbial nutrient metabolisms were co-limited by N and P, particularly P during plant secondary succession. Therefore, microbial communities were co-limited by C, N, and P, particularly C and P during plant secondary succession, and the limitation was mainly associated with soil nutrient status.