Abstract: Clarifying the effects of wetland degradation on nitrogen-transforming gene abundance of soil microorganisms provides an important basis for understanding wetland degradation mechanism and scientific management of degraded alpine wetlands. We detected the gene abundance of nitrogen-fixing bacteria (nifH), ammonia oxidizing archaea (AOA amoA), ammonia oxidizing bacteria (AOB amoA) and denitrifying bacteria (nirK) in Gahai wetland soils under four different degrees of degradation (non-degraded, lightly degraded, moderately degraded and severely degraded), by real-time fluorescent quantitative PCR technology. We further analyzed the characteristics of functional gene abundances under different degradation stages. The results showed that the abundances of the four functional genes were significantly higher in the 0-10 cm soil layer than that in the 10-20 cm soil layer. The gene abundance of nifH, AOA, AOB and nirK ranged 10⁶-10⁸, 10⁷-10⁸, 10⁵-10⁶ and 10⁷-10⁸ copies·g^-1 soil, respectively, while the abundance of AOA was significantly higher than that of AOB. The abundances of the four genes peaked in the lightly degraded stage, and significantly decreased in the moderately and severely degraded stages. The interpretation rates of soil physical and chemical properties for the variations of soil microbial functional genes were 87.9% and 91.2%, respectively, with the key drivers differing in different months. Soil water content was the key factor affecting gene abundance in June, while nitrogen content was the key factor driving the variations of gene abundance in August.

Key words: wetland degradation, soil microbe, functional gene, nitrogen, gene abundance.