Effects of N addition and clipping on above and belowground plant biomass, soil microbial community structure, and function in an alpine meadow on the Qinghai-Tibetan Plateau

Nitrogen (N) enrichment and grazing are two factors that have profound effects on grassland ecosystem processes and functions. This study evaluated separate and combined effects of clipping and N addition on soil properties, soil microbial community structure, and soil extracellular enzyme activity within our experiment design which included three clipping intensities (i.e., unclipped, moderate, and heavy clipping) and two different N treatments (with and without N addition) in an alpine meadow ecosystem on the Qinghai-Tibetan Plateau, China. Results revealed that N addition alone did not significantly affect total soil organic carbon (TOC), total soil N (TN), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and N (MBN) after 3 years of treatments. The moderate clipping alone increased root exudation rates whereas the heavy clipping decreased root exudation rates, TOC, TN, DOC, MBC and MBN, fungi biomass, and the ratio of fungi to bacteria. The effects of N addition were generally neutral or negative in the heavy clipping treatment. In contrast, N addition significantly increased aboveground biomass, MBC, MBN, DOC, and soil water content but decreased inorganic N in the moderate clipping. RDA analysis showed that N addition could stimulate soil microbial community structure in the moderate clipping treatment by impacting the availability of labile soil C. Our results improve the understanding of the role of N addition in regulating soil C storage among different grazing intensities in alpine meadows