| Stipa breviflora desert steppe has special species composition and community type,fragile ecological environment and sensitive response to grazing.The influence of different grazing intensity on population is different,which leads to the change of the relationship between plant populations.In order to study the relationship between the main plant populations of Stipa breviflora Desert Steppe under different grazing intensities,the main plant populations of Stipa breviflora Desert Steppe in Inner Mongolia(Stipa breviflora,Allium polyrhizum and Cleistogenes songorica)were selected as the research objects,and three grazing treatments(no grazing,medium grazing and heavy grazing)were adopted in the randomized block experiment design.From 2015 to 2019,the data of population density and aboveground biomass of main plants were obtained by random sampling method,and the spatial data of main plant population were obtained by mechanical sampling method,and the soil nutrient data were measured.Combining with variance analysis,grey correlation analysis,canonical principal component analysis and geostatistical analysis,the response of the main plant population function and population interrelation to grazing disturbance in Stipa breviflora desert steppe was analyzed from the aspects of main plant population and community dynamics,niche,soil resource distribution pattern and population spatial distribution pattern,and the following conclusions were obtained.(1)With the increase of grazing time and intensity,the population density,important value and aboveground biomass of Stipa breviflora decreased gradually.The density of main plant population and the ratio of aboveground biomass to community in the dry year are relatively large.With the increase of grazing time,the proportion of main population decreased.The interannual climate has a great impact on the population and community dynamics of the main plants,and grazing interference will reduce the impact.(2)When the population is in the same density,its interspecific affinity takes the form of symmetry.In the middle density of main plant population,the species compatibility is the strongest,and in the high density,the species compatibility is the weakest.The species groups of Stipa breviflora and Cleistogenes songorica have a large spatial distribution heterogeneity in the presence of relatively low density,and the spatial distribution variability is the smallest in the area of medium density distribution.The spatial distribution of Allium polyrhizum population is more complex in the presence of relatively high density.(3)Under different grazing treatments,the niche width of the main plant population is larger than that of other plant populations in the community,and the niche width of the awnless Cleistogenes songorica is larger than that of Stipa breviflora and Allium polyrhizum.With the increase of grazing intensity,the niche width of Stipa breviflora and Cleistogenes songorica awnless increased gradually,while that of Allium polyrhizum decreased gradually.The change of niche overlap degree of main plant population is related to the competition ability of species and the affinity degree of species,and there is asymmetry.(4)With the increase of grazing intensity,the correlation between species with weak correlation in plant community disappeared.Under different grazing treatments,the relationship between species affinity and competition is asymmetric.Grazing disturbance increased the intraspecific competition intensity and weakened the interspecific competition intensity,and the interspecific affinity was the highest under moderate grazing intensity.(5)No matter whether there is grazing disturbance or not,and how the grazing intensity changes,the scale of random distribution of the main population gradually increases,and with the increase of the scale,the random distribution gradually changes to the aggregate distribution.The response of spatial heterogeneity of plant population to grazing intensity was specific.Under moderate grazing,the spatial distribution variability of Allium polyrhizum was the most complex,while that of Stipa breviflora and Cleistogenes songorica was the opposite.When the plant population is clustered distribution,its intraspecific competitiveness is stronger,while the plant population under the condition of uniform distribution and random distribution has stronger interspecific competitiveness.The aggregation distribution of species is an important reason for the multi degree asymmetry of interspecific relationship.Different grazing treatments have a greater impact on the number of individuals in the plant population.When the number of individuals decreases,the species tend to aggregate distribution.(6)Grazing increased the content of nitrogen and potassium,and decreased the content of phosphorus.Without grazing disturbance,the spatial distribution of soil organic carbon,total nitrogen,alkali hydrolyzed nitrogen,available phosphorus and total potassium was mainly affected by random factors;after grazing disturbance,the spatial distribution of soil organic carbon,total nitrogen,alkali hydrolyzed nitrogen,available phosphorus and total potassium was mainly affected by structural factors.Heavy grazing can strengthen the heterogeneity of spatial distribution of soil nutrient content,while moderate grazing can weaken the heterogeneity of spatial distribution of soil nutrient content.(7)Under the influence of grazing intensity and soil resource limitation,the relationship among the main plant populations(Stipa breviflora,Allium polyrhizum and Cleistogenes songorica)in desert steppe is affected by multiple factors,among which the response of density effect is the strongest.Under different grazing intensity,the content of soil potassium has a great influence on the main plant population,community dynamics and spatial distribution.The relationship between plant population and soil nutrients is affected by plant species.The relationship between Allium polyrhizum and Cleistogenes songorica and soil nutrients is greater than Stipa breviflora. |
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