Abstract:

In this study, we aimed to explore the response mechanism of soil bacterial community composition and diversity under the background of increasing nitrogen deposition and conducted a short-term field simulation experiment with four nitrogen-level treatments: control (0 g·m⁻²·a⁻¹), low (5 g·m⁻²·a⁻¹), medium (10 g·m⁻²·a⁻¹), and high nitrogen (15 g·m⁻²·a⁻¹), in the Carex nubigena community in an alpine degraded Napahi meadow. High-throughput sequencing was used to systematically analyze the effects of plant and soil physicochemical properties on bacteria under nitrogen addition. The results showed the following: 1) Nitrogen addition significantly affected the soil bacterial community composition at the phylum level. With an increase in nitrogen concentration, the relative abundances of Acidobacteriota, Actinomycetota, Methylomonas, Gemmatimonadota, and Nitrospira first increased and then decreased, with an increase of 1.05% to 38.24% compared with the control. The relative abundance of Proteobacteria and Firmicutes increased by 6.02%-90.24% compared to the control, while those of Chloromycota, Myxococcus, Bacteroidetes, and Verrucomicrobiota showed a decreasing trend of 14.25%-36.18%. At the genus level, Acidobacterium, Gemmatimonas, Vicinamibacter, and RB41 showed a trend of first increasing and then decreasing, Micrococcus and Xanthobacter showed a trend of first decreasing and then increasing, and Candidatus Solibacter showed an increase. 2) Nitrogen addition significantly increased the aboveground plant biomass and decreased the plant diversity. The aboveground plant biomass increased by 65.4%, whereas the Shannon, Simpson, Margalef, and Pielou indices decreased by 13.9%-24.6%. Nitrogen addition significantly affected soil physicochemical properties. With the increase in nitrogen concentration, in contrast with the control, available potassium, organic matter, and available nitrogen increased by 7.04%-59.48%; total potassium and pH value decreased by 4.7%-18.18%; total and available phosphorus decreased by 1.67%-34.52% under the low nitrogen treatment and then increased. 3) Changes in plant and soil environments significantly affected the bacterial community under nitrogen deposition. Structural equation analysis showed that changes in plant diversity indirectly regulated the composition and diversity of the bacterial community by affecting soil nutrients, whereas changes in the soil environment directly affected the bacterial community. Total soil nutrients, available nutrients, and pH were the main factors controlling bacterial community changes. Short-term nitrogen addition directly or indirectly regulates soil bacterial diversity and phylum composition by mediating changes in plant diversity and pH and affecting soil nutrient content.

Key words: nitrogen addition, alpine meadow, soil bacteria, diversity, community structure, Napahai

摘要：

为探明土壤细菌群落对氮沉降增加的响应机制，以纳帕海高寒退化草甸云雾薹草（Carex nubigena）群落土壤为研究对象，野外设置对照（0 g·m⁻²·a⁻¹）、低氮（5 g·m⁻²·a⁻¹）、中氮（10 g·m⁻²·a⁻¹）和高氮（15 g·m⁻²·a⁻¹）等4种氮添加量的模拟试验，采用高通量测序测定土壤细菌群落组成及多样性，分析氮添加下植物和土壤环境变化对细菌群落的影响特征。结果表明，1）氮添加显著影响土壤细菌门属水平群落组成。随氮量增加，酸杆菌门、放线菌门、甲烷氧化菌门、芽单胞菌门、硝化螺旋菌门相对丰度先增后减;变形菌门、厚壁菌门相对丰度增加;绿弯菌门、粘菌门、拟杆菌门、疣微菌门相对丰度降低;在属水平上，酸杆菌属、芽单胞杆菌属、Vicinamibacter、RB41先增后减，微球菌属、黄杆菌属先减后增，Candidatus Solibacter增加。2）氮添加显著影响植物与土壤环境。随氮添加量增加，地上生物量增加而植物多样性降低;土壤速效钾、全氮、有机质、速效氮含量增加，全钾、pH降低;全磷、速效磷呈先减后增趋势。3）氮添加下植物变化通过影响土壤养分而间接调控土壤细菌，土壤环境变化则直接影响细菌群落。结论：氮添加主要通过改变植物多样性、土壤pH和土壤养分含量，直接或间接对土壤细菌产生影响。

关键词: 氮添加, 高寒退化草甸, 土壤细菌, 多样性, 群落结构, 纳帕海