Above- and below-ground responses to grazing in alpine grasslands: insights from carbon allocation and dynamic in plant-soil-microbe system

Abstract

Aims Grazing is a widely utilization of natural grasslands globally, yet the impacts of grazing intensity on the short-term carbon (C) cycling dynamics between above- and below-ground remain inadequately understood. Methods we employed an experiment to identify how these changes under grazing intensities (non-grazing, NG; moderate grazing, MG; and heavy grazing, HG), which combined with an in-situ 13C tracing between plant tissues and soil microbes in alpine grassland. Results 13C was rapidly detected in shoots, roots, soils, and microbial PLFAs after first day of pulse labeling day. Comparison to NG, the root δ13C values were significantly higher under MG than under HG during the chase period (p < 0.01). PLS-PM revealed that MG significantly enhanced the 13C allocation from shoots to roots (p < 0.05), while leading to a significant decrease in the turnover of root 13C into microbial PLFA 13C amount and 13CCr (p < 0.05), and a significant reduction in soil 13C turnover into microbial 13CCr (p < 0.05). HG significantly enhanced the turnover of soil 13C into PLFA 13C amount (p < 0.05), resulting in a significant improvement in microbial PLFA 13C amount turnover into microbial 13CCr (p < 0.05), and leading a significant decrease in root 13C turnover into microbial 13CCr (p < 0.05). Conclusions Grassland under MG maintains high C retention between shoots and roots, forming a strong negative cascading relationship with microorganisms in the rhizosphere, but HG enhances the utilization of rhizodeposits by microbes, establishing a strong positive cascade relationship.