Study On Plant Community Characteristics Of Lespedeza Davurica And Artemisia Sacrorum Communities In The Loess Plateau Hilly Region Of Northern Shaanxi

In this paper,Lespedeza davurica and Artemisia sacrorum communities are chose as the main objects in the Loess Plateau Hilly region of northern Shaanxi China.Through field investigation and indoor analysis,vegetation survey and soil samples of 22 samples were measured.The ecological niche,species diversity,biomass and soil nutrients and microbial characteristics of typical communities in this area were analyzed from the perspective of growth years.This paper discusses the influence of ecological factors on community characteristics and the relationship between microorganism and soil nutrient characteristics,and further evaluates the adaptability of typical community to ecological factors.It provides scientific basis for restoration and reconstruction of vegetation in this area.The main results are as follows:1.Ecological niche and environmental interpretation of dominant population in Lespedeza davurica communities.In the community of Lespedeza davurica,the population of Lespedeza davurica,Stipa bungeana and Artemisia sacrorum has strong adaptability,high resource utilization and wide niche breadth.The niche breadth of Dracocephalum moldavica,Rhaponticum uniflorum and Viciayvillosa is relatively small,indicating that it has poor adaptability to environment and low resource utilization.The average value of Lespedeza davurica niche overlap index in different growth years is increased first and then decreased.The average value of the ecological niche overlap index of Lespedeza davurica,Stipa bungeana and Artemisia sacrorum is the highest in 17 a.In addition,with the increase of the growth years,the proportion of the population niche overlap index greater than 0.5 in the community also increases first and then decreases,and reaches the maximum in 17 a.It indicates that the niche overlap phenomenon in the 17 a community is obvious,and there is a high similarity in various groups biological characteristics and resource demand.The niche breadth of the population is mainly affected by aspects and growth years,and the ecological niche overlap is mainly influenced by aspects and altitude.2.Ecological niche and environmental interpretation of dominant population in Artemisia sacrorum communities.In the Artemisia sacrorum community,Artemisia scoparia,Lespedeza davurica,Heteropappus altaicus,Stipa bungeana,Artemisia sacrorum,Agropyron cristatum,Oxytropis tragacanthoides,and Artemisia giraldii has larger total niche breadth.They have great adaptability to the environment and are the dominant species of community.The ecological niche width value of the Artemisia sacrorum increased first and then decreased,and reached the maximum value in 18 a.The ecological niche width of the Stipa bungeana,Heteropappus altaicus and Lespedeza davurica is the trend of fluctuation,and they all reach the maximum value of 24 a.The proportion of species that niche overlap value is greater than 0.5 in the early recovery(5-9 a)change in a fluctuant way,and later period(13 to 30 a)is to reduce rising trend again after rising first,and has a maximum value in the 30 a community.This shows that in the 30 a community,the competition among species is fiercest.The slope gradient and growth years are the main ecological factors that affect the ecological niche width and ecological niche overlap.3.Species diversity and its environmental interpretation of Artemisia sacrorum communities.The diversity of species and soil physical,chemical and biological properties are different in different aspects.Except for Peilou’s evenness index of sunny slopes > shade slopes,other diversity indices show that the shady slope is higher than the sunny slope.The indicators of soil physicochemical properties and microbial properties also show the tendency of the shady slope to be higher than that of the sunny slope.In the same area,the general climate is generally the same,so the main factors affecting plant diversity are differences in niches(microorganisms,soil nutrients,soil moisture,and bulk density).This study also conclude that Peilou and Simpson diversity index were significantly positively correlated with slope gradient,soil bulk density and urease.Aspect and altitude have a great influence on Patrick Simpson advantage index.Aspect,slope gradient and altitude are the most influential factors driving the species diversity changes of Artemisia sacrorum communities.4.Community characteristics and environmental interpretation of Lespedeza davurica communities.With the increase of growing years,the above-ground biomass and its ratio of the community of Lespedeza davurica all firstly increased,then decreased and then increased,and the underground and above-ground biomass reache its maximum at 17 a.Underground/aboveground biomass is at its maximum at 13 a.The Peilou evenness index and Simpson dominance index first increased(7-17a)and then decreased(22-32a)with the increase of growth years,while the Shannon-Wiener index,Simpson diversity index,and Patrick richness index are opposite and reached the maximum at 32 a.The contents of soil organic nitrogen,organic carbon,available phosphorus,available potassium(0-5,5-10cm)and microbial biomass carbon and nitrogen all decreased first and then increased.Soil nutrient changes in the 10-20 cm layer are not obvious.The species diversity and abundance of communities are greatly influenced by the orientation of the slope.The underground biomass,evenness,and dominance of the community are greatly affected by the gradient.The above-ground biomass is greatly affected by the microbial biomass carbon and nitrogen.In short,the characteristics of the Lespedeza davurica community are the result of a combination of ecological factors that are dominated by slope orientation.5.Characteristics of soil nutrients and their relationship with soil microbial in Artemisia sacrorum communities.With an increase in the number of growth years,soil microbial biomass carbon and nitrogen contents as well as soil phosphatase and urease activities initially decreased and then increased in the A.sacrorum communities.The soil organic carbon,organic nitrogen,and total nitrogen contents as well as soil respiration rate showed an increasing trend and reached a maximum at age(a)37.The soil available phosphorus content first decreased and then increased,with the lowest level observed at 18 a.By contrast,soil available potassium initially increased and then decreased.Soil microbial biomass carbon had a significant positive correlation with soil organic carbon,total nitrogen and organic nitrogen,while soil respiration had a significant positive correlation with organic nitrogen,soil phosphatase and organic carbon.Soil respiration had a highly significant positive correlation with organic carbon and total nitrogen,while soil phosphatase had a highly significant positive correlation withtotal nitrogen and organic nitrogen.In the A.sacrorum communities,the soil organic carbon and total nitrogen contents were mainly affected by soil respiration,soil available potassium content was mainly affected by soil urease activity,and soil organic nitrogen content was mainly affected by soil phosphatase activity.These findings indicate that SR,urease activity and phosphatase activity were the major microbial factors affecting the characteristics of the soil nutrients in the A.sacrorum communities.In conclusion,the natural restoration process of A.sacrorum communities can enhance soil microbial activity and improve soil quality.In summary,with the changes of ecological factors such as the growth period,aspect and gradient,the adaptability of the ecological niche and species diversity of Lespedeza davurica and A.sacrorum community were different.The population niche of the Lespedeza davurica communities was mainly affected by the aspect,the growth years,and the altitude;the A.sacrorum community was mainly affected by the slope gradient and the growth years.Aspect,elevation,soil moisture content,organic carbon and microbial biomass carbon are the most influential factors driving the species diversity of A.sacrorum community.Aspect,slope gradient and microbial biomass carbon and nitrogen are important factors affecting the distribution of Lespedeza davurica community.Soil respiration,urease and phosphatase activities were the main microbial factors affecting soil nutrient characteristics in the A.sacrorum community.In general,the natural restoration of Lespedeza davurica and A.sacrorum communities had a significant effect on the restoration of vegetation and improvement of soil quality in the Loess Hilly Region of northern Shaanxi.According to the influence of ecological factors on the community characteristics and the rational allocation of plant characteristics,it is helpful to achieve a better vegetation restoration effect.