The Patterns Of Arbuscular Mycorrhizal Fungi And Their Response To Livestock Grazing In Major Grasslands In Northern China

Grasslands is one of the most widely distributed terrestrial ecosystems in the world,distributed on all continents except Antarctica.It is estimated that they account for onefifth of the earth's land surface.Grasslands have important economic significance.First,they provide high-quality forage for animal husbandry,and secondly,they provide beautiful natural landscapes for leisure and tourism activities.Arbuscular mycorrhizal fungi(AMF)are ubiquitous in grasslands.They play an important role in ecosystem functions and services.So far,AMF has been found in grasslands with different soil and vegetation types around the world,including tropical grasslands,arid grasslands and temperate grasslands.However,there are relatively few studies on the AMF community structure of different grassland types in northern of China,and its driving mechanism is still unclear.In addition,the impact of livestock grazing in grassland ecosystems on biological communities including AMF is complex and profound.Livestock can affect AMF in grassland ecosystems through direct and indirect effects.In the past,there has been a lot of understanding about the effects of grazing intensity on AMF,but there are often differences in characteristics of grazing livestock,and the current understanding of the impact mechanism of livestock assemblage on grassland is still lacking.This study carried out grazing control experiments on meadow grasslands,typical grasslands and desert grasslands in northern China,revealing the influence of grassland types and diversified livestock grazing methods on the assembly of AMF community and the mechanism of action.In view of the fact that the AMF community structure is affected by the grassland type,and at the same time is significantly disturbed by grazing.Therefore,the research first carried out regionalscale control experiments to reveal the differences in the composition,diversity and network structure of AMF communities on different grassland types in northern China;on this basis,in order to explore the effects of grazing livestock and host plants on grassland AMF.The study set up grazing control experiments on three types of grasslands,and further studied the response of AMF community structure to grazing livestock assemblages and host plants on local scale.The main results of the research are as follows:(1)There are obvious differences in the AMF community composition,diversity,and network complexity among different grassland types in northern China.AMF in the grassland ecosystem of northern China is mainly composed of Glomus and Diversispora,Scutellospora,Paraglomus,and Acaulospora,among which Glomus is most dominant taxa.The AMF community structure of the three grassland types was significantly different.The AMF species diversity(OTU level)of the desert steppe was greater than that of the typical steppe and meadow steppe,while the interspecific relationship of the meadow steppe AMF community was the highest,and the desert steppe had the lowest degree value of the co-occurence network.The results of CCA analysis showed that the average annual rainfall played a major role in driving the formation of the AMF community pattern in the grassland ecosystem in northern China.(2)In the grassland ecosystem of northern China,the effect of host plants identity on AMF community structure is relatively small.Except that the host plant species have a certain influence on the abundance of individual genus of AMF,there is no strong one-to-one symbiotic relationship between host plants and AMF.The number of AMF genera shared by different host plants is much larger than the number owned by individuals.The AMF community structure of the same host plant in different grassland ecosystems was significantly different.However,the difference of AMF community structure among different host species in the same grassland type is not obvious.These results indicate that the formation of AMF community structure by host plants mainly depends on the habitat conditions rather than the host plant identity.(3)Livestock grazing experiments were conducted on three grasslands.it is found that grazing has a significant impact on the AMF community of grassland.Grazing livestock has a tendency to reduce the diversity of AMF by reducing the biomass of plant land and reducing the organic carbon content passed by plants to symbiotic AMF.Different body sizes have different effects on the AMF community due to their selective feeding differences.Cattle need a large amount of food resources to meet their demand for feed intake.Therefore,they mainly feed on dominant plants in large quantities,which in turn causes a large loss of biomass of dominant plant,and then has a significant impact on the AMF community.However,Sheep's appetite is small,mainly feed on plants with higher nutrients,and mainly eat the delicate stems and leaves of plants,so it has little impact on the AMF community that coexists with dominant plants.In addition,grazing reduces the above-ground biomass of plants and promotes the secondary growth of plants.Plants need to absorb more nutrients in the soil to meet their growth needs.Therefore,AMF needs to form a closer interspecific relationship,that is,a more complex co-occurrence network.Therefore,the complexity of the cooccurrence network of the AMF community in the grazing is higher than that of the non-grazing,and the network has more nodes and edges.(4)AMF is not randomly distributed.Our results showed that,on local scale,the physical and chemical properties of soil,grazing type,and host plants identity play a driving role in the assembly of AMF community structure.In the meadow steppe,typical steppe and desert steppe,grazing has a greater driving effect on the assembly of AMF community than soil factors and host plant identity.And the host plant has a significantly higher selection effects on AMF community in the root than in the rhizosphere soil.At the regional scale,the assembly of AMF community in the grassland ecosystem in northern China is affected by multiple factors,such as abiotic factors,grazing types,and host plants identity.Abiotic factors play a more important role in the assembly of AMF community in rhizosphere soil and root than grazing methods and host plants identity.The host plant indentity has a greater impact on the assembly of AMF community in root than on rhizosphere soil.This study is based on the spatial distribution pattern of AMF communities in grassland ecosystems in the northern China.We analyzed the driving factors of the distribution pattern of AMF communities in grassland ecosystems.We found that multiple factors such as grassland types,grazing and host plants indentity have effects on the community structure of AMF.This study provides some experience for the further exploration of AMF community structure in grassland,and can provide relevant theoretical basis for grassland ecosystem biodiversity conservation and grassland grazing management.The results of the study show that livestock grazing will reduce the AMF diversity level of grassland ecosystems,but will increase the tightness of the AMF community co-occurence network.The study also shows that the effects of grazing livestock species on the assembly of grassland AMF community structure are also quite different.In the current background of grassland degradation.It is particularly important to pay attention to the grazing of livestock combination.In the management of grassland,in addition to the traditional management of grazing intensity.it is also necessary to formulate suitable livestock based on vegetation conditions such as grassland productivity and plant diversity,combined with the monitoring of AMF community composition,diversity and network structure.Combination of grazing methods to avoid the imbalance of the relationship network between the grassland biological communities and prevent the population outbreak of certain species from causing accelerated grassland degradation.