高寒草原退化过程中植被和土壤因子对微生物群落的交互影响

Interaction Effects of Vegetation and Soil Factors on Microbial Communities in Alpine Steppe Under Degradation

为了探明青藏高原高寒草原退化过程中植被和土壤因子对土壤微生物群落的调节作用,以青藏高原三江源区高寒草原为研究对象,分析了不同退化阶段(未退化、中度退化和重度退化)高寒草原植被及土壤因子的差异,利用高通量测序技术分析了不同退化阶段微生物群落特征,并借助冗余分析(RDA)和基于相似或相异度矩阵的多元回归(MRM)识别影响微生物(细菌和真菌)群落变化的关键环境因子.结果表明,高寒草原退化显著改变了群落盖度、高度、生物量及禾本科重要值,降低了土壤有机质、全氮、全磷含量和粉粒含量,增加了土壤容重和砂粒含量.退化并未改变细菌和真菌的组成,但改变了组成比例,导致了微生物丰富度(Chao1指数和Richness指数)的损失,但并未显著改变微生物多样性(Shannon指数),随着退化的发生,植被特征、土壤理化性质与微生物多样性呈现出了一致的变化趋势.结合网络拓扑变化特征(网络的节点数和聚类系数显著下降)发现,高寒草原退化导致了微生物的种间相互作用减弱,网络结构更加分散,微生物的分布趋向于均质化,但物种间的相互作用仍然以合作为主(网络正相关连接占比>90%).高寒草原退化过程中植被-土壤的耦合对土壤细菌群落的影响最大,而土壤理化性质对土壤真菌的群落影响最大.具体而言,植被群落高度、生物量及土壤容重是调节土壤微生物的共性因子,植被辛普森指数、禾本科重要值、土壤全磷、全钾和粉粒含量是影响土壤细菌群落的特有因子;而土壤pH和全氮含量是影响土壤真菌群落的特有因子.

To clarify the regulating effect of vegetation and soil factors on microbial communities in the alpine steppe under degradation on the Qinghai-Xizang Plateau,the alpine steppe in the Sanjiangyuan area of the Qinghai-Tibet Plateau was chosen.We analyzed the differences in vegetation and soil factors in different stages of degradation(nondegradation,moderate degradation,and severe degradation)and detected the variations in microbial community characteristics in the alpine steppe under different degradation stages using high-throughput sequencing technology.Eventually,redundancy analysis(RDA)and multiple regression matrixes(MRM)based on the similarity or dissimilarity matrix were used to identify key environmental factors regulating microbial(bacterial and fungal)community changes under degradation.The results showed that the degradation of the alpine steppe significantly changed the community coverage,height,biomass,and important value of graminae;significantly reduced the contents of soil organic matter,total nitrogen,total phosphorus,and silt;and increased the soil bulk density and sand content.Degradation did not change the composition of bacteria and fungi,but their composition proportions changed and also resulted in the loss of microbial richness(Chao1 index and Richness index)but did not significantly change the microbial diversity(Shannon index).With the occurrence of degradation,the vegetation characteristics,soil physicochemical properties,and microbial diversity showed a consistent change trend.Combined with the characteristics of the network topology changes(the number of nodes and clustering coefficient significantly decreased),it was found that degradation of the alpine steppe led to the decline of interspecies interactions,decentralization of network,and homogenization of microorganisms,but the cooperation relations among the species were maintained(positive correlation connections accounted for more than 90%in all degradation stages).Under the alpine steppe degradation,the vegetation-soil interaction had the greatest effect on soil bacterial community,whereas soil physicochemical properties had the greatest influence on soil fungal community.Specifically,vegetation community height,biomass,and soil bulk density were the mutual factors regulating soil microorganisms,whereas the vegetation Simpson index,important value of graminae,soil total phosphorus,total potassium,and silt content were the unique factors affecting the soil bacterial community,and soil pH and total nitrogen content were the particular factors affecting the soil fungal community.