模拟氮沉降和降雨变化对贝加尔针茅草原土壤细菌群落结构的影响

Effects of simulated nitrogen deposition and precipitation change on soil bacterial community structure in a Stipa baicalensis steppe

研究氮沉降和降雨变化对土壤细菌群落结构的影响,对未来预测多个气候变化因子对草地生态系统影响的交互作用具有重要意义。以施氮和灌溉分别模拟氮沉降和降雨增加,采用高通量测序技术,研究8个氮添加水平(0、15、30、50、100、150、200、300kg N hm-2a-1)和2个水分添加水平(不灌溉、模拟夏季增雨100 mm灌溉)对土壤细菌群落结构的影响。结果表明,氮素和水分输入增加后,土壤细菌群落组成、丰度均显著变化(P<0.05)。在群落中占主导的细菌门类有疣微菌门Verrucomicrobia(30.61%—48.51%)、变形菌门Proteobacteria(21.37%—29.97%)、酸杆菌门Acidobacteria(9.54%—20.67%)和拟杆菌门Bacteroidetes(4.96%—9.74%)。在常规降雨和水分添加两种条件下,随着氮添加水平的增加,占主导的细菌门类(相对丰度>1%)表现出不同的变化趋势。疣微菌门相对丰度在常规降雨N100—N300条件下显著降低,但在氮素和水分同时添加条件下随氮添加水平升高而逐渐升高,在N200—N300时显著升高。变形菌门和拟杆菌门相对丰度在常规降雨高氮添加条件下呈升高趋势,但在水分添加时却无明显变化。酸杆菌门相对丰度在常规降雨高氮添加条件下升高,但在水分添加后呈明显下降趋势。放线菌门Actinobacteria相对丰度在常规降雨N100—N300条件下显著升高,但在水分添加后高氮添加时显著降低。厚壁菌门Firmicutes相对丰度在常规降雨条件下无显著变化,但在水分和高氮添加条件下降低。浮霉菌门Planctomycetes相对丰度在两种不同的水分添加条件下均呈先升高后降低的趋势。氮素和水分添加对土壤细菌群落结构的变化存在明显的互作效应(P<0.0001)。在不同氮素和水分输入条件下共有19个土壤细菌门类相对丰度有显著差异。土壤细菌群落结构的变化主要来自于疣微菌门和酸杆菌门的相对丰度变化,两者可作为土壤细菌群落结构变化的指示种。综上,氮素和水分添加显著改变了土壤细菌群落结构,氮素和水分对土壤细菌不同门类相对丰度变化存在明显的互作效应。

Nitrogen （N） deposition and precipitation change are important phenomena in global climate change and they can strongly influence grassland ecology. There have been many studies on the response of plant and soil microbial communities to N addition. However, the interactive effects of N addition and irrigation on soil microbial communities are still largely unknown. Studying the effects of nitrogen （N） deposition and precipitation change on soil microbial community structure is of great significance for predicting the interactive effects of multiple climate factors on grassland ecosystems in the future. Here, we simulated N deposition and precipitation change by N addition （0, 15, 30, 50, 100, 150, 200, 300 kg N hm^-2a^-1） and irrigation （no irrigation and irrigation equivalent to 100 mm extra summer rainfall） at a test area on the Stipa baicalensis steppe. A split-plot design was adopted. Soil samples were collected with a soil probe after four years of experimental treatments. Using high-throughput sequencing technology, we evaluated the interactive effects of N addition and irrigation on the soil bacterial community structures. Statistical analyses showed that N addition and irrigation significantly （P 〈 0.05） shifted the composition and relative abundance of the soil bacterial community.The dominant bacterial phyla were Verrucomicrobia （30.61%-48.51%）, Proteobacteria （21.37%-29.97%）, Acidobacteria （9.54%-20.67%）, and Bacteroidetes （4.96%-9.74%）. Under normal precipitation, the relative abundance of Verrucomicrobia significantly decreased in N100-N300 （P 〈 0.05）, but the relative abundance of Proteobacteria, Acidobacteria, Actinobacteria and Bacteroidetes increased with high N addition levels. However, the relative abundance of Firmicutes did not significantly change. When water was added with N, the relative abundance of Verrucomicrobia increased following the increase of N addition rates and significantly increased in N200-N300, but the relative abundance of Acidobacteria, Firmicutes and Actinobacteria decreased after N addition. The relative abundance of Proteobacteria and Bacteroidetes did not significantly change under N addition combined with irrigation. The ANOVA of the split-plot design showed that N addition and irrigation interactively affected the structure of the soil bacterial community. The results of the Linear Discriminant Analysis （LDA） showed that the relative abundance of 19 bacterial phyla significantly shifted under different N and water addition rates. The changes in soil bacterial community structure were mainly related to changes in the relative abundance of the phyla Verrucomicrobia and Acidobacteria. Hence, phyla Verrucomicrobia and Acidobacteria could be used as indicator species for changes in soil bacterial community structure. In all, N addition and irrigation significantly changed the structure of the soil bacterial community. N and water addition interactively affected the relative abundance of different soil bacterial phyla.