青藏高原高寒湿地春夏两季根际与非根际土壤反硝化速率及nirS型反硝化细菌群落特征分析

反硝化是生态系统氮循环的关键过程.目前对于生态系统氮排放及反硝化细菌群落的研究大多基于人为影响显著的环境，对于人为干扰较低的自然生态系统的研究较少.本研究选取青藏高原黄河源区不同海拔（唐克、久治、玛多和达日）不同季节（春季和夏季）的高寒湿地植物根际与非根际土壤作为研究对象，采用¹⁵N同位素标记法测定反硝化速率，高通量测序技术测定nirS反硝化细菌群落组成及相对丰度，并探究环境因子（气温、海拔）和土壤理化性质（pH、土壤有机碳、铵态氮、硝态氮和亚硝态氮）对nirS型反硝化细菌群落的影响.结果表明，高寒湿地土壤反硝化速率范围为0.80~14.98 nmol·（g·h）^-1，对总N₂释放的贡献率为11.23%~71.16%.唐克、久治和达日的土壤样品，均呈现出根际土壤反硝化速率高于非根际的趋势（P<0.05）.Proteobacteria是青藏高原高寒湿地植物根际和非根际土壤中主要的反硝化细菌门；在属水平上，各土壤样本中相对丰度最高的是一种未分类的变形杆菌（unclassified Proteobacteria，2.86%~29.41%），这表明主导青藏高原高寒湿地反硝化作用的可能有一些独特的未被鉴定的反硝化菌属，相对丰度其次为假单胞菌属（Pseudomonas，2.45%~26.52%）和贪铜菌属（Cupriavidus，0%~34.14%）.基于距离的冗余分析结果表明，高寒湿地的反硝化细菌群落结构主要受到海拔、pH、NO₂^-含量影响（P<0.05）；相关分析表明反硝化速率和Shannon指数与pH呈显著负相关（P<0.05），且主要反硝化菌群相对丰度受到温度和pH的影响.本研究结果可为进一步了解青藏高原高寒湿地这一特殊生境中的氮循环提供参考依据.

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

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.