Abstract: We examined the impacts of degradation and artificial restoration of alpine grasslands on microbial communities and the related carbon cycling functions, with experiments being conducted on degraded alpine meadows and artificially restored grasslands in the Qinghai-Tibet Plateau. With metagenomic techniques, we analyzed the change of microbial structures and carbon cycling functions, and further explored the environmental factors driving the changes of carbon cycling functional genes. The results showed that degradation and artificial restoration of grasslands significantly altered soil and vegetation characteristics. The increase of soil microbial richness and diversity and the decrease of the relative abundance of dominant species indicated that microbial community tended to be homogeneous during degradation and artificial restoration of grasslands. The diversity of soil carbon cycling functional genes showed a trend of increasing, stabilizing, and increasing. The top 15 dominant species contributed more than 40% to carbon cycle functional genes, and such contribution decreased significantly under degradation and restoration of grasslands. The effect of individual soil or vegetation on microbial community structure was greater than that on microbial carbon cycling functional genes, while soil and vegetation interaction had stronger effect on the latter than the former. Specifically, carbon cycling functional gene diversity and abundance were significantly related to soil available nitrogen (ammonium nitrogen and nitrate nitrogen) and vegetation factors (coverage, biomass, and diversity). Our results contribute to a better understanding of microbial mechanisms of carbon cycling during meadow degradation and artificial restoration.

Key words: Qinghai-Tibet Plateau, Three-River Headwaters region, metagenomics, degraded alpine meadow, artificial restoration, carbon cycling functional genes