[Denitrification Rates and nirS-type Denitrifying Bacteria Community Structure Characteristics of Bulk and Rhizosphere Soil in Spring and Summer in the Alpine Wetlands of the Qinghai-Tibet Plateau].

Abstract

Denitrification is a key process in the nitrogen cycle of ecosystems. Most existing studies of nitrogen emissions and denitrifying bacterial communities are carried out in ecosystems with significant human interference, yet few focus in natural ecosystems with low human disturbance. Here, the denitrification rates and characteristics of nirS-type denitrifying bacterial communities in rhizosphere and bulk soils from alpine wetland plants at different altitudes(Tangke, Jiuzhi, Maduo, and Dari) and seasons(spring and summer) in the Yellow River source region of the Qinghai-Tibet Plateau were investigated. The 15N isotope tracer technique was used to estimate the denitrification rates, and high-throughput sequencing technology was used to determine the composition and relative abundance of nirS-type denitrifying bacterial communities. We also investigated the environmental factors(temperature and altitude) and soil physical and chemical properties(pH, soil organic carbon, ammonia, nitrate, and nitrite) controlling the denitrification and related microorganisms. The results show that the denitrification rates of alpine wetland soils ranged from 0.80 to 14.98 nmol·(g·h)-1, and the contribution to the total N2 production ranged from 11.23% to 71.16%. The soil samples from Tangke, Jiuzhi, and Dari showed higher denitrification rates in rhizosphere soils than the corresponding bulk soils(P<0.05). Proteobacteria was the most dominate denitrifying bacteria phylum. At the genus level, unclassified Proteobacteria(2.86%-29.41%) showed the highest relative abundance, indicating that unique unidentified bacteria may dominate denitrification in these wetland soils. The genera with the next highest relative abundances were Pseudomonas(2.45%-26.52%) and Cupriavidus(0%-34.14%). Distance-based redundancy analysis showed that the community structure of the nirS-type denitrifying bacteria was mainly affected by altitude, pH, and nitrite concentrations; Pearson correlation analysis showed that denitrification rates and the Shannon index are significantly negatively correlated with soil pH(P<0.05), and the relative abundance of the main denitrifying bacterial genera were influenced by temperature and soil pH(P<0.05). This study provides valuable insights for understanding the nitrogen cycle in the unique alpine wetlands of the Qinghai-Tibet Plateau.