Effects of nitrogen enrichment on soil enzyme activities in grassland ecosystems in China: A multilevel meta-analysis
Jibo SHI, M. Motior Rahman, Ruonan Ma, Qiang Li, Yingxin HUANG, Guangdi Li
Abstract
Nitrogen (N) enrichment has resulted in widespread alteration of grassland ecosystem processes and functions mainly through disturbance in soil enzyme activities. However, we lack a comprehensive understanding of how N deposition affects specific key soil enzymes that mediate plant-soil feedback of grassland. Here, with a meta-analysis on 1 446 cases from field observations in China, we show that N deposition differently affects soil enzymes associated with soil biochemical processes. Specifically, N-promoted C, N, and P-acquiring hydrolase activities significantly increased by 8.73%, 7.67%, and 8.69%, respectively, related to an increase in microbial-specific enzyme secretion. The increased relative N availability and soil acidification were two potential mechanisms accounting for the changes in soil enzyme activities with N enrichment. The mixed N addition in combination of NH 4 NO 3 and urea showed greater stimulation effect on soil enzyme activities. However, the high rate and long-term N addition tended to weaken the positive responses of soil C-, N- and P-acquiring hydrolase activities to N enrichment. Spatially increased mean annual precipitation and temperature primarily promoted the positive effects of N enrichment on N- and P-acquiring hydrolase activities, and the stimulation of C- and N-acquiring hydrolase activities by N enrichment was intensified with the increase in soil depth. Finally, multimodal inference showed that grassland type was the most important regulator of responses of microbial C, N, and P-acquiring hydrolase activities to N enrichment. This meta-analysis provides a comprehensive insight into understanding the key role of N enrichment in shaping soil enzyme activities of grassland ecosystems.