Study On Sensitive Indices To Vegetation And Soil And Succession Characteristics In Degradation Grass/White Clover Grasslands

Grass/white clover(Trifolium repens)grassland is one of the main mixed pastures in southern China,which plays an important role in the development of local grass animal husbandry.Previous studies have systematically analyzed the characteristics of plant species relationships,nutrients,community composition and grassland stability on grass/white clover grasslands,etc.,subsequently,the sensitive indices to vegetation and soil and succession characteristics in the process of grasslands degradation is not clear.In this study,grasses(Dactylis glomerata+ Perennial ryegrass)/white clover grasslands in Xundian,Yunnan and Zhuopu,Guizhou were selected as the objects,the characteristics of plant populations(tillers density,weight and number of in plant cluster of main grasses,stolon density and weight of Trifolium repens),plant community(species composition,diversity,biomass and nutrients)and soil(nutrients,p H,bulk density)of grasslands with different degrees of degradation were analyzed.The key indicators of vegetation and soil,and the co-evolution pattern of plant populations and communities in the process of grassland degradation were clarified.The main results are as follows:With the increase of grassland degradation grades,the plant diversity indexes(Patrick richness,Shannon-Winer,Pielou uniformity and Simpson dominance)in Xundian grasslands increased,while it firstly decreased and then increased in Zhuopu grasslands.The proportion of living matter and planting forages,contents of total N and total P and feeding value indexes(DMI,DDM,RFV,ME,GI,DOMD)of forages,densities both plant and tiller of Dactylis glomerata,stolon density of Trifolium repens decreased in the two study areas,while the proportion of dead matter and the contents of NDF,ADF,cellulose and hemicellulose of forages increased.Plant diversity,functional groups biomass,nutritional value of forages,density of Dactylis glomerata number and Trifolium repens stolon were sensitive to degradation.With the increase of grassland degradation grades,the contents of total N,organic matter and available P in the soil of Xundian grasslands almost decreased,while the total P,alkali-hydrolyzed N and p H values in Xundian grasslands and the soil nutrients(organic matter,N,P)in Zhuopu grasslands had no significant changes.The p H values increased and the bulk density first decreased and then increased in Zhuopu grasslands.There was a significantly negative correlation between grassland plant diversity indexes and underground biomass in Zhuopu grasslands.Shannon-Winer,Pielou uniformity and Simpson dominance indices of plant were positively correlated with NDF of forages,and negatively correlated with forages DDM in two experimental areas.The biomass of sown forages was positively correlated with total N,total P,DMI,DDM,RFV and DOMD of forages,and negatively correlated with NDF,ADF,hemicellulose and cellulose.The key indicators of grass/white clover grassland degradation are plant diversity,biomass composition,nutrient value of forages and population density of sown forages;and total N,organic matter and available P contents of soil.Vegetation is more sensitive to grasslands degradation than soil.In the process of the grasslands degradation,the proportion of sown forages decreased due to the decreases of their population density,the increase of invasive weeds and plant diversity reduces the density and composition of sown forgae,which leads to the deterioration of forage quality.