贝加尔针茅草原土壤真菌群落结构对氮素和水分添加的响应

Response of soil fungal community structure to nitrogen and water addition in Stipa baicalensis steppe

研究氮沉降和降雨变化对土壤真菌群落结构的互作效应,对未来预测多个气候变化因子对草地生态系统的交互作用具有重要意义。以施氮和灌溉模拟氮沉降和降雨增加,采用裂区设计,应用高通量测序技术,研究8个氮添加水平(0、15、30、50、100、150、200、300 kg N hm^(-2)a^(-1))和2个水分添加水平(不灌溉、模拟夏季增雨100 mm灌溉)对土壤真菌群落结构的影响。结果表明,氮素和水分添加后,土壤真菌群落中占优势的门类分别为接合菌门Zygomycota(22.0%—48.9%)、担子菌门Basidiomycota(7.8%—18.5%)、子囊菌门Ascomycota(9.4%—20.1%)、球囊菌门Glomeromycota(0.7%—3.1%)、壶菌门Chytridiomycota(0.1%—1.3%)。常规降雨条件下,随着氮添加水平升高,接合菌门相对丰度呈现出先升高后降低的趋势,N50处理最高;子囊菌门相对丰度在高氮添加时(N100—N300)呈升高趋势。而在氮素和水分同时添加条件下,随着氮添加水平升高,接合菌门相对丰度呈降低趋势,子囊菌门相对丰度变化则不明显。在相同的氮添加水平下,水分添加使接合菌门相对丰度增加,而担子菌门、子囊菌门、球囊菌门和壶菌门的相对丰度降低。在不同氮素和水分添加条件下,有5个土壤真菌门类11个真菌纲相对丰度变化显著。接合菌门的Mortierella属,担子菌门的Entolomataceae科和Geastrum属相对丰度变化极显著,可作为土壤真菌群落结构变化的指示种。PCo A分析结果也表明氮素和水分添加改变了土壤真菌群落结构。植物-土壤-微生物系统的结构方程模型结果表明,植物群落组成及植物物种丰富度的变化是土壤真菌群落结构发生变化的主要影响因素,土壤无机氮及p H的变化主要通过影响植物群落间接影响真菌群落,其对真菌群落的直接影响则较小。综上,氮素和水分添加改变了土壤真菌群落结构,且两者存在明显的互作效应,水分添加可改变氮添加对土壤真菌群落的影响。

Nitrogen （N） deposition and precipitation change are important phenomena in global climate change and can greatly influence grassland ecosystems. Soil fungal communities are a functionally diverse group and they mediate many ecological processes as well as influence plant growth and soil health. There have been many studies on the responses of plant and soil bacterial communities to N addition. However, the interactive effects of N and water addition on soil fungal communities remain largely unknown, with these interacting effects having great significance for predicting the future effects of multiple climate factor changes on grassland ecosystems. In the present study, we simulated N deposition and precipitation change by N addition （0, 15, 30, 50, 100, 150, 200, and 300 kg N hm^-2 a^-1） and irrigation （no irrigation and irrigation equivalent to 100 mm extra summer rainfall）. Utilizing split-plot design and high-throughput sequencing technology, we evaluated the interactive effects of N and water addition on soil fungal community structure. Statistical analyses showed that N and water addition significantly shifted the composition and relative abundance of soil fungal communities. The dominant fungal phyla were Zygomycota （22.0%-48.9%）, Basidiomycota （7.8%-18.5%）, Ascomycota （9.4%-20.1%）, Glomeromycota （0.7%-3.1%）, and Chytridiomycota （0.1%-1.3%）. Under normal precipitation, the relative abundance of Zygomycota increased in N1-N50 treatments and decreased in N100-N300 treatments. The relative abundance of Ascomycota increased in the N100-N300 treatments. When water was added, the relative abundance of Zygomycota decreased; however, the relative abundance of Ascomycota showed no significant change. At identical N levels, water addition increased the relative abundance of Zygomycota; however, the relative abundance of Basidiomycota, Ascomycota, Glomeromycota, and Chytridiomycota decreased. The relative abundance of all 5 fungal phyla and 11 fungal Classes shifted significantly under different N and water addition rates. The changes in soil fungal community structure are mainly related to the changes in relative abundance of genus Mortierella, family Entolomataceae, and genus Geastrum. Hence, genus Mortierella, family Entolomataceae and genus Geastrum could be utilized as indicator species to signify changes in soil fungal community structure. The results of Principal Coordinate Analysis （PCoA） also revealed that N and water addition significantly modified the structure of the soil fungal community. Structural equation modeling of the integrated response of the plant-soil-microbe system to N and water addition demonstrated that plant community composition and plant species richness were the main factors causing shifts in the soil fungal community. Soil inorganic N and pH indirectly affected the structure of soil fungal community via the plant community. Overall, N and water addition changed the structure of the soil fungal community by interactively affecting the relative abundance of different soil fungal phyla. Therefore, water addition modified the effects of N addition on the soil fungal community.