Characteristics And Adaptive Mechanism Of Endophytic Fungi Community Of Oxytropis Ochrocephala In The Eastern Qinghai-Tibet Plateau

Oxytropis ochrocephala is a kind of poisonous grass of Oxytropis in grassland.It is widely distributed in the alpine grassland of Western China and distribution is expanding year by year with the aggravation of grassland degradation in China.Most of the studies on Oxytropis ochrocephala also focus on the mechanism of livestock poisoning,alkaloid composition,nutritional value,control and utilization.There is a lack of research on the community characteristics of endophytic fungi in Oxytropis ochrocephala and its response mechanism to environmental changes.Thus,in this study,Oxytropis ochrocephala and soil samples were collected from five different altitudinal gradients(3064m,3327 m,3610m,3901 m and 4200m)and three population densities(low density,medium density and high density)in the eastern of Qinghai Tibet Plateau.Using high-throughput sequencing technology,principal component analysis,correlation analysis and redundancy analysis and other classical statistical methods to analyze the changes of community structure,composition,diversity and functional characteristics of endophytic fungi in Oxytropis ochrocephala under the change of growth environment.At the same time,through the construction of molecular ecological network model,the network structure of microbial community of Oxytropis ochrocephala in different growth environments was analyzed,so as to reveal the adaptation mechanism of endophytic fungi of Oxytropis ochrocephala to the changes of growth environment,and provide theoretical basis and practical guidance for the effective control and rational utilization of Oxytropis ochrocephala.The main research results were showed as following:1)The height of grass layer decreased,the coverage of grassland increased first and then decreased,and the vegetation diversity increased with the increase of altitude.With the increasing of altitude,the nutritional quality of Oxytropis ochrocephala increased first and then decreased.At the same time,the soil characteristics of Oxytropis ochrocephala growing area changed significantly.And altitude gradient was significantly correlated with crude ash content,soil p H and soil N,P and K content of Oxytropis ochrocephala Population expansion increased the biomass of Oxytropis ochrocephala growing area,but also decreased the height,coverage and diversity of grass layer,which changed the composition of community to a certain extent.Population expansion not only decreased the quality of Oxytropis ochrocephala,but also changed the soil characteristics of Oxytropis ochrocephala growing area.It has no significant correlation with soil organic carbon and grass layer height,but also has different degree correlation with other environmental factors.2)The diversity and composition characteristics of Endophytic Fungi Community in Oxytropis ochrocephala changed with the elevation,which first increased and then decreased,reaching the highest at 3300 ? 3600 m,and the community richness increased with the elevation.The dominant phylum of endophytic fungi in Oxytropis ochrocephala at different altitudes were Ascomycota,Basidiomycota and Mortierellomycota,the dominant class were Leotiomycetes,Tremellomycetes and Dothideomycetes,and the dominant genus were Filobasidium,Alternaria,Botrytis and Mortierella.The diversity and richness of Endophytic Fungi Community in Oxytropis ochrocephala decreased due to the population expansion.The dominant phylum of endophytic fungi in Oxytropis ochrocephala at different population densities were the same as those in the altitude gradient,but the dominant class were Dothideomycete,Agaricomycetes and Leotiomycetes,and the dominant genus were Alternaria.These results indicated that a few species with high abundance dominated the community structure of endophytic fungi in Oxytropis ochrocephala.With the refinement of taxonomy,the response characteristics of endophytic fungi were more accurately reflected.3)The community structure of endophytic fungi in Oxytropis ochrocephala was significantly changed with the change of altitude.The lefse analysis showed that there were 42 different species in Oxytropis ochrocephala at different altitudes.And Redundancy analysis and mantel analysis showed that the contents of crude protein and ash,organic carbon,total nitrogen,total phosphorus and p H in soil were the main factors affecting the community structure of endophytic fungi in Oxytropis ochrocephala at different altitudes.In fact,Population expansion did not significantly change the community structure of endophytic fungi in Oxytropis ochrocephala.Lefse analysis showed that there were only four different species in Oxytropis ochrocephala with different population density.Redundancy analysis and mantel analysis showed that the changes of endophytic fungal community structure in the process of population expansion were significantly related to nutrient content,soil bulk density,p H,water content,total nitrogen and total phosphorus content.4)Based on the functional prediction of endophytic fungi in Oxytropis ochrocephala at five altitudes,it was found that the endophytic fungi communities in Oxytropis ochrocephala were mainly symbiotic and saprophytic.The functional trophic types of endophytic fungi in Oxytropis ochrocephala were significantly different among different altitudes,and there were more pathological trophic types in low altitudes.The functional types of endophytic fungi in Oxytropis ochrocephala were different in different parts of the plant.The root was mainly saprophytic,while the branches and flowers were mainly symbiotic and pathotrophic.The functional prediction of Endophytic Fungi Community in Oxytropis ochrocephala with three different population densities showed that the population expansion caused changes in the functional characteristics of endophytic fungi in Oxytropis ochrocephala.With the increase of population density,the symbiotic and saprophytic types of endophytic fungi in Oxytropis ochrocephala decreased,while the pathological type increased.Therefore,population expansion may increase the toxicity of Oxytropis ochrocephala.5)The molecular ecological network model between endophytic fungi and environmental factors in different habitats showed that the stability of community structure of endophytic fungi in Oxytropis ochrocephala was affected by habitat change.The loose and unstable structure of molecular ecological network model of endophytic fungi in Oxytropis ochrocephala was caused by elevation and population expansion.Low elevation and low density had higher organization and functionality.The community structure of endophytic fungi in Oxytropis ochrocephala was closely related to soil total nitrogen,total potassium and organic carbon,and strongly related to vegetation coverage,crude protein content,crude fiber content,soil bulk density and soil p H in population expansion.In conclusion,the community structure of endophytic fungi in Oxytropis ochrocephala was limited by vegetation and soil factors,and interacted with soil,plant and microorganism.The change of growth environment changes the characteristics of soil and plants,and then affects the endophytic fungi.On the contrary,the change of endophytic fungi causes the change of the characteristics of plants and growing areas.