Study On Relationship Between The Patch Density Of Ligularia Virgaurea And Vegetation And Soil In Alpine Meadow

Ligularia virgairea,a dominant poisonous grass,can cause changes in the structure and function of the ecosystem.Any changes in ecosystem diversity and community composition will likely alter production-ecological function provided by that ecosystem.However,what are the advantages of L·virgaurea in toxic grass degraded grassland ecosystem?and how does L·virgaurea facilitate population expansion by affecting alpine grassland vegetation and soil environment?These mechanisms are poorly understood.This project takes the micro-patches of L·virgaurea with different densities as the object,six spread degrees（D0,D1,D2,D3,D4,D5）were divided according to the density level,and systematically analyzed the changes of community structure,plant nutrients,soil nutrients and soil microorganisms in different densities patches of L·virgaurea.This paper expounds the correlation among degraded grassland community,soil physical and chemical properties and soil microorganisms,and reveals the synergistic changes of plant,soil and microorganisms in grassland ecosystem after L·virgaurea damage.The results will provide a theoretical basis for preventing the further expansion of L·virgaurea population and the restoration and reconstruction of ecosystem production-ecological function of alpine poisonous grass type degraded grassland ecosystem.The results showed that:（1）With the increase of the density of L·virgaurea,the dominant forage was gradually replaced by L·virgaurea,the proportion of edible forage was decreased.The species diversity increased at first and then decreased,and the diversity index had higher value when the density of L·virgaurea was between D1～D2.Total aboveground biomass after removing L·virgaurea and total underground biomass had the highest value at D1.When the density of L·virgaurea was between D1 and D2,it had a positive effect on the maintenance of grassland stability.However,when the density exceeded D4,grassland diversity and productivity were destroyed,leading to grassland degradation.（2）The soil nutrient content can be increased when the density of L·virgaurea was within a certain range.With the increase of the density of L·virgaurea,the contents of the soil water,total nitrogen,total phosphorus and total potassium were increased,the p H value and the contents of nitrate nitrogen were significantly decreased（P<0.05）.The nutrient accumulation of L·virgaurea limited the nutrient competition of other forage grass.Soil nitrate nitrogen,p H value and density of L·virgaurea were significantly correlated（P<0.05）,and soil nutrient status of grassland was the best when the density of L·virgaurea was in D2.（3）The activity of catalase and sucrase were not significantly affected by the density of L·virgaurea,the activity of neutral phosphatase increased significantly,and urease reached the maximum value in D1 and then significantly decreased（P<0.05）.With the increase of the density of L·virgaurea,MBC showed an inverted‘V’trend,and MBN and MBP showed an‘N’type change.Soil catalase,sucrase and neutral phosphatase were positively correlated with microbial biomass,and soil enzyme activity and microbial biomass had a certain synergistic relationship with soil nitrogen.the p H value played an important role in soil nitrogen cycling.（4）L·virgaurea could accumulate higher organic carbon,the nitrogen content of functional group plant were relatively stable,while the phosphorus content of Forbs was relatively high.With the increase of the density of L·virgaurea,the carbon content of community showed an increasing trend,nitrogen content increased slightly and then decreased significantly,phosphorus content decreased at first and then increased.C:N ratio of L·virgaurea was significantly higher than that of other functional groups（P<0.05）.The C:P and N:P of L·virgaurea decreased significantly with the increase of the density.When the density of L·virgaurea was greater than or equal to 40 plants·0.25m^-2,both plants and soil of patches were restricted by nitrogen,and the requirement of nitrogen was greater than that of phosphorus in the grassland community.There was a significant correlation between soil microbial activity and organic matter content of plants and soil,and the correlation between the stoichiometric characteristics of plant and stoichiometric characteristics of soil and microbial biomass was significant（P<0.05）.（5）The dominant bacteria were Proteobacteria,Acidobacteria,Planctomycetes,Verrucomicrobia and Actinobacteria,and Ascomycota,Basidiomycota and Mortierellomycota were the dominant fungal in patches of L·virgaurea.At the level of genus classification,the abundance of RB41 was the highest with soil bacteria.Mortierella is the dominant group of soil fungi,and the relative abundance of D4was significantly higher than that of the other patches.Hygrocybe is the dominant group in D1 and D3.Theα-diversity index of soil bacterial community had no significant difference among different patches,while theα-diversity index of fungal community was the highest in D2.The composition of soil bacterial community in D0,D2 and D3 were basically similar,and there was a great difference between D5and other patches.The soil fungal communities in D0,D2,D4 and D5 were closely,fungal communities of D1 and D3 were similar,and there were great differences in fungal community composition between D1,D3 and D2.（6）The carbohydrate metabolism,amino acid metabolism and cofactor and vitamin metabolism were the most active in soil bacteria with different density patches,and he abundance of D3 showed a relatively low level in predictive function.D0 significantly inhibited the expression of partial metabolism,the level of bacterial functional genes gradually increased with the increase of L·virgaurea density,and D5 significantly enriched the expression of Xenobiotics biodegradation and metabolism.The most of the fungal nutrient types came from pathological bacteria,symbiotic trophic bacteria and saprophytes in density patches.There were differences in the relative abundance of functional genes of soil fungi in different patches,and the dominant groups of soil fungi in different density patches were Endophyte-Litter Saprotroph-Soil Saprotroph-Undefined Saprotroph.（7）Soil indexes,such as soil p H,nitrate nitrogen,microbial biomass nitrogen and phosphorus,neutral phosphatase etc.,were significantly correlated with vegetation characteristics in patches of different densities of L·virgaurea（P<0.05）.Soil bacteria were significantly correlated with soil nitrate nitrogen,total potassium,microbial biomass phosphorus,p H,neutral phosphatase and urease（P<0.05）.Soil fungi were closely related to soil total nitrogen,total phosphorus,available phosphorus,available potassium,water content,catalase and sucrase.Shannon index and Simpson index of soil bacteria were positively correlated with underground biomass and total biomass of grassland,and Chao1 index of soil fungi was significantly positively correlated with Simpson index of grassland vegetation,and ACE index was positively correlated with Pielou index,Simpson index,total aboveground biomass and Gramineae biomass of vegetation（P<0.05）.Vegetation characteristics had significant negative effects on density of L·virgaurea,soil physical and chemical properties had significant positive effects on density of L·virgaurea（P<0.01）,while microbial diversity had no significant positive and negative effects on density of L·virgaurea（P>0.05）.