Background and aims Changes in nitrogen (N) and precipitation levels can substantially alter soil properties and plant growth, thereby altering soil microbial diversity and functionality. Method We used manipulated precipitation treatments (50% reduction, control, and plus 50%) and tested two N fertilization levels (control and plus 35 kg N ha −1 yr −1 ) from a 4-year field experiment to evaluate the effects on soil bacterial diversity, community composition, and N-cycle gene abundance. Results N additions significantly increased ammonia-oxidizing bacterial abundance (via AOB- amoA ) but decreased denitrification genes (i.e., nirS and nosZ ). Decreased precipitation significantly decreased the abundance of N-cycle genes (AOB- amoA , nirS , and nosZ ), while increased precipitation conversely increased the abundance of these same genes. Decreased precipitation led to differences in the microbial community composition that favored drought resistance, indicating that plant-associated microbiomes may be able to modulate plant growth fitness in the context of extreme environmental conditions. N additions substantially altered soil bacterial communities, increasing the relative abundance of certain bacteria and of nitrification-related genes in a manner that depended on precipitation fluctuations. Conclusions Differences in the bacterial community composition and N-cycle genes determined the functional response of a grassland ecosystem to decreased precipitation conditions, and therefore could affect the influence of N deposition on plant growth as well as the physical and chemical properties of the soil.

中文翻译：

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沙漠草原细菌群落和植物介导的土壤过程对氮沉降和降水的响应

背景和目标 氮 (N) 和降水水平的变化可以显着改变土壤特性和植物生长，从而改变土壤微生物多样性和功能。方法 我们使用人工降水处理（减少 50%、控制和加 50%）并测试了来自 4 年田间试验的两种施氮水平（控制和加 35 kg N ha -1 yr -1 ），以评估对土壤细菌多样性、群落组成和 N 循环基因丰度。结果 N 添加显着增加了氨氧化细菌的丰度（通过 AOB-amoA），但减少了反硝化基因（即 nirS 和 nosZ）。降水减少显着降低了 N 循环基因（AOB-amoA、nirS 和 nosZ）的丰度，而降水增加反而增加了这些基因的丰度。降水减少导致微生物群落组成的差异，有利于抗旱，表明植物相关微生物组可能能够在极端环境条件下调节植物生长适应性。氮的添加显着改变了土壤细菌群落，以依赖于降水波动的方式增加了某些细菌和硝化相关基因的相对丰度。结论 细菌群落组成和氮循环基因的差异决定了草地生态系统对降水减少条件的功能响应，因此可能影响氮沉降对植物生长的影响以及土壤的理化性质。