不同密度布氏田鼠对内蒙古典型草原菌根真菌群落的影响

Effects of different densities of Brandt’s voles on communities of mycorrhizal fungal in the typical steppe of Inner Mongolia

布氏田鼠是内蒙古典型草原的主要啮齿类动物,其活动既可以改变植物群落组成和多样性,又可以改变土壤理化性质,进而潜在影响与绝大多数草原植物共生的重要土壤微生物-丛枝菌根真菌(AMF),但目前关于啮齿动物活动对AMF群落组成和多样性影响的研究鲜有报道。基于此,依托内蒙古自治区锡林浩特市毛登牧场的大型野外布氏田鼠围栏实验平台,选择其中3个田鼠密度处理(低、中、高密度,对应的初始投放布氏田鼠数量分别为12、24和48只·样地^(-1)),利用Illumina Miseq测序技术分析不同密度布氏田鼠处理对AMF群落的影响,采用标准网格交叉法测定根系侵染率和土壤菌丝密度,探究布氏田鼠活动对典型草原AMF群落的影响机制和作用途径。主要结果表明:1)在土壤样品中共鉴定到6科9属的AMF,其中优势属为球囊霉属(Glomus);2)高密度布氏田鼠处理显著降低了植物生物量、植被盖度、群落丰富度和多样性,显著降低土壤水分、pH,显著增加土壤硝态氮含量;显著降低AMF侵染率、菌丝密度、丰富度和多样性;3)相关性分析表明,菌丝密度与植物丰富度、多样性指数、土壤pH和含水量显著正相关,与硝态氮含量显著负相关;侵染率与植物多样性指数、土壤pH和含水量显著正相关;AMF多样性指数与土壤pH和含水量显著正相关,不同操作分类单元(OTU)丰富度与植物多样性指数和pH显著正相关;4)NMDS和PerMANOVA分析显示AMF群落结构在低密度和高密度处理间差异显著,其中土壤NO_(3)^(-)和pH是影响AMF群落组成的主要因子。因此,布氏田鼠密度过高会导致植物群落生物量、多样性以及土壤养分含量下降,同时两者的改变导致了AMF群落多样性显著降低,可能会加速典型草原的退化。

Brandt’s vole(Lasiopodomys brandtii)is the main rodent in typical steppe grassland of Inner Mongolia,China. Its activities can change the composition and diversity of plant communities and the physical and chemical properties of soil. It follows that Brandt’s vole activity could potentially affect the community composition and diversity of arbuscular mycorrhizal fungi(AMF),one the of most important groups of soil microbes living in association with the majority of grassland plant species. However,little is known about the influences of Brandt’s vole activities on AMF. To investigate the effect of rodent activities on the community structure and composition of AMF,we conducted field sampling from plots treated with different densities of rodents(initial numbers of rodents per plot were 12,24 and 48 for low,medium and high rodent densities,respectively) in Maodeng Ranch,Xilinhaote,Inner Mongolia. AMF communities in soil samples were analyzed with Illumina sequencing,and root mycorrhizal colonization rate and hyphal density were evaluated using a standard grid intersect method. 1)A total of six families and nine genera of AMF were identified in soil samples,among which the dominant genus was Glomus.2)High density treatment of Brandt’s voles reduced plant biomass,vegetation cover,community richness and plant diversity,and reduced soil moisture and pH,but increased soil nitrate content and reduced AMF richness and diversity,root colonization rates and hyphal length density in soil. 3)Hyphal length density was positively correlated with the richness and diversity of plant communities,and with pH and moisture,but negatively correlated with nitrate content. AMF colonization was positively correlated with plant diversity,pH and moisture,but AMF diversity was positively correlated with soil pH and moisture. Operational taxonomic unit abundance of AMF was positively correlated with plant diversity and moisture. 4)Non-metric multidimensional scaling and permutational MANOVA analyses showed that AMF community structure differed between low-density and high-density rodent treatments and that NO_(3)^(-) and pH were the main factors driving the changes in AMF community composition. Based on these findings,we conclude that high density of Brandt’s voles will lead to a decrease in plant community biomass and diversity and soil nutrient content,and these changes will in turn lead to a significant decrease in AMF community diversity,which may accelerate the degradation of typical steppe.