Contrasting potential impact patterns of unique and shared microbial species on nitrous oxide emissions in grassland soil on the Tibetan Plateau

Microbial nitrogen transformation processes in grasslands are important nitrous oxide (N2O) sources on the Tibetan Plateau. Different microorganisms carrying various functional nitrogen (N) cycling genes colonize different soil types and have varying impacts on N2O emissions. However, the role of specific microbial com-ponents such as unique and shared microbial species, in N2O flux in alpine grassland soils remains understudied. Thus, we combined gas chromatography-based static opaque chamber methods with metagenomic sequencing to investigate the role of unique and shared microbial species carrying N-cycling genes in N2O emissions from two alpine grassland types on the Tibetan Plateau. Our results showed that the N2O flux in the alpine meadows (9.48 x 10-9 g m- 2 h-1) was higher than that in the alpine steppes (4.21 x 10-9 g m- 2 h-1). Furthermore, our study revealed a significant negative correlation between the abundance of unique microbial species and the N2O flux in alpine steppes. In contrast, the abundance of shared microbial species was significantly and positively correlated with N2O flux. The unique microbial species in the phyla Chloroflexi and Actinobacteria carried the ureC, nasA and nirB genes, which could consume nitrogen substrates in forms other than producing N2O, which could explain the N2O reduction seen in the alpine steppes. In addition, the higher abundance of shared microbial species in the phyla Proteobacteria, Actinobacteria, Thaumarchaeota and Acidobacteria carried genes encoding denitrification pathways (nirK, narG, and norB) could interpret the higher N2O emissions in the alpine meadows. In addition, our study revealed that the soil substrate contents (e.g., soil organic carbon and total nitrogen) and soil environment factors (e.g., soil pH and soil moisture) were potentially important drivers of N2O emissions in soil via their regulation of the composition of unique and shared microbial communities carrying N-cycling genes. Collectively, our results suggested that identifying the unique and shared microbial species carrying different N-cycling genes could provide potential biological strategies for mitigating N2O emissions in alpine grasslands, such as blocking the growth of shared microbial species. Future management practices for mitigating N2O emissions in alpine grassland should also focus on adopting appropriate nutrient management strategies, such as balanced fertilization, to prevent excessive nutrient. Our findings provide insights for further elucidating the different potential regulatory effects of unique and shared microbial species on emissions under the control of the soil environment in different types of grasslands on the Tibetan Plateau.