Nitrogen Significantly Affected N Cycling Functional Gene Abundances Compared with Phosphorus and Drought in an Alpine Meadow

Abstract

Human activities and global climate change have greatly increased nitrogen (N) and phosphorus (P) inputs and altered precipitation patterns in alpine meadows. Functional genes are important indicators of microorganisms that drive the nitrogen cycling process; however, the functional gene responses of soil nitrogen cycling to soil N and P availability and drought remain unclear. Separate or combined treatments of nitrogen and phosphorus fertilization and drought were conducted on the Zoige Wetland in the Qinghai-Tibet Plateau, and the abundances of nitrification functional genes AOA amoA and AOB amoA and denitrification functional genes nirS, nirK, and nosZ were measured to explore the response of functional genes to these treatments. Seven treatments, including control (CK), N addition (N), P addition (P), 50% reduction in precipitation (D), N and P addition (NP), N addition with drought (ND), and NP addition with drought (NPD), were investigated. The results indicated that N application significantly increased AOB amoA abundance, while P application and drought had no significant effects on the abundance of functional genes. The combined treatment of N and P addition and drought increased AOB amoA abundance but did not significantly affect AOA amoA abundance, suggesting that AOB amoA was more responsive to soil N and P availability and moisture change than AOA amoA. However, the abundance of denitrification functional genes was not affected by these treatments. Denitrification functional genes were less sensitive to soil N and P availability and moisture change than nitrification functional genes. The integrated effects of N addition, P addition, and drought did not affect the abundance of the above N cycling functional genes. These results indicate that AOB amoA may play a more critical role in the process of ammonia oxidation than AOA amoA in alpine meadows, and the denitrification genes (nirK, nirS, and nosZ) were better than ammoxidation genes (AOA and AOB) at adapting to the soil environmental changes caused by increasing N and P deposition and drought in alpine meadows.