Effects of Simulated Nitrogen Deposition and Precipitation Manipulation on Soil Microorganisms in the Desert Steppe of Northern China

ABSTRACT: Soil microorganisms are influenced by climate change. However, the effect of climate change on soil cultivable bacteria are unclear. In this study, the composition and diversity of the soil cultivable bacterial community were explored by a dilution–plate method, PCR, and 16S rRNA sequencing in a desert steppe of northern China after repeated NH4NO3 amendments and precipitation manipulation for seven years. The experimental treatments were as follows: control (CK), N addition (+N), N addition plus water addition (+N+W), and N addition plus water reduction (+N-W). Among the treatment groups, 11 genera and 17 bacterial species were isolated. Nitrogen addition and precipitation manipulation significantly increased the number of cultivable bacteria in the 0.00-0.30 m layer compared to CK. Compared to +N treatment, the +N+W and +N–W treatments had no significant impact on the number of cultivable bacteria. Compared to the CK community, bacterial communities exposed to the other three treatments did not show shifts in the relative abundance of dominant genera and other cultivable bacteria, except for Pontibacter and Staphylococcus. The treatments +N+W and +N-W significantly modified the relative abundance of Pontibacter and Staphylococcus compared to the +N treatment. Available potassium and phosphorus, and moisture content contributed to the change in the composition of the cultivable bacterial community (p>0.05). Nitrogen addition and precipitation manipulation significantly decreased species richness in the 0.00-0.02 m layer, but they did not affect evenness and the Shannon-Wiener Index in the 0.00-0.30 m layer. This study provides insights into how the composition and diversity of the bacterial community is affected by climate change scenarios.

摘要：土壤微生物受气候变化影响，但气候变化对土壤可培养细菌的影响尚不明确。本研究以中国北方荒漠草原为研究对象，在历经7年反复施加硝酸铵（NH₄NO₃）并调控降水的野外试验基础上，采用稀释平板法、聚合酶链式反应（PCR）以及16S rRNA测序技术，对土壤可培养细菌群落的组成与多样性展开探究。试验设置如下处理组：对照组（CK）、单施氮处理（+N）、施氮增水处理（+N+W）以及施氮减水处理（+N-W）。本次试验共分离得到11个菌属、17个细菌物种。与对照组相比，施氮及降水调控处理显著提升了0.00~0.30 m土层中的可培养细菌数量。相较于单施氮处理，施氮增水与施氮减水处理对可培养细菌数量无显著影响。与对照组群落相比，其余三种处理组的细菌群落中，除桥杆菌属（Pontibacter）与葡萄球菌属（Staphylococcus）外，优势菌属及其他可培养细菌的相对丰度均未发生显著改变。相较于单施氮处理，施氮增水与施氮减水处理显著改变了桥杆菌属与葡萄球菌属的相对丰度。速效钾、速效磷与土壤含水量是影响可培养细菌群落组成变化的驱动因子（p>0.05）。施氮及降水调控处理显著降低了0.00~0.02 m土层的物种丰富度，但对0.00~0.30 m土层的物种均匀度及香农-威纳指数（Shannon-Wiener Index）无显著影响。本研究为理解气候变化情景下细菌群落组成与多样性的响应机制提供了理论参考。