Altered intra-annual precipitation patterns affect the N-limitation status of soil microorganisms in a semiarid alpine grassland

Abstract

The ongoing intensification of the hydrological cycle due to global climate change alters intra-annual precipitation variability. Changes in precipitation patterns lead to disparities in soil moisture; however, the responses of soil extracellular enzyme activities (EEAs) and microbial metabolism limitations to them is unclear. This study conducted an in situ field experiment in the alpine grasslands of the Kunlun Mountains to simulate the same amount of precipitation but change the distribution time of precipitation within the plant growing season. We examined the effects of variability in intra-annual precipitation patterns on the stoichiometry of topsoil (0–5 and 5–20 cm) properties, microbial biomass, and EEAs. Results showed that altered precipitation patterns significantly increased soil moisture’s disparity index (D) by 57 %–89 %. The activity of nitrogen-acquiring enzymes (L-leucine aminopeptidase) was increased by 20.82–32.08 % (P < 0.05) with increased variability of precipitation, while phosphorus-acquiring enzymes (Acid phosphatase) and carbon-acquiring enzymes (β-glucosidase) both decrease by 9.25–23.35 % and by 17.86–33.04 %, respectively (P < 0.05). We determined that soil microorganisms in the study region were metabolism-limited by nitrogen (vector angles < 45◦), and increased precipitation variability exacerbated nitrogen limitation (decrescent vector angles) and alleviated carbon limitation (shortened vector length). In addition, soil EEAs can be both interactively influenced by biotic and abiotic factors, with abiotic factors (i.e., D, soil organic carbon content, and soil total nitrogen content) having a stronger effect. Our study provides an effective strategy for regulating soil EEAs, microbial biomass, and microbial metabolism limitation and contributes to developing nutrient management and restoration strategies in semiarid alpine grassland ecosystems.