Quantitative Characteristics And Their Responses To Grazing Of Three Plant Populations In Typical Steppe Of Loess Plateau

Plant population quantitative traits are the most basic characteristics of the community.Studying the population characteristics and age structure of grassland plants can predict the development trend of grassland communities and reveal the adaptability mechanism of grassland plant species to the environment.In the past,there was a lack of research on the age class division of grassland plants,and the research on the population characteristics of grassland plants at the age level was relatively insufficient.We used four grazing intensities(0,2.67,5.33,and 8.67 SU/hm~2,that is CK,LG,MG and HG,respectively)in typical steppe in Longdong Loess Plateau to study the population quantitative characteristics of Stipa bungeana,Lespedeza davurica and Artemisia capillaris,including plant height,crown diameter,base diameter,number of tillers/branches,weight per plant,tiller/branch weight and herbage nutrient content.Its purpose is to clarify the differentiation characteristics and age patterns of the three plant species,and to determine the grazing intensity of the study area.It will provide some theoretical and practical basises for revealing adaptation mechanism of plant population to habitat and steppe rational use.The main results are as followings:(1)With the increasing of plant age,the population characteristics of Stipa bungeana,Lespedeza davurica and Artemisia capillaris including plant height,crown diameter,base diameter,numbers of tillers/branches,weight per plant,and tiller/branch weight showed a gradually increasing trend.Moreover,the proportion of small plants of three plants showed a decreasing trend.the proportion of large plants showed a increasing trend.Finally the plants showed an ageing trend.With grazing intensity increasing,the plant height and crown diameter of Stipa bungeana in the 9th year of rotational grazing,crown diameter and base diameter of Lespedeza davurica in the 9th and 11th year of rotational grazing,the plant height of Artemisia capillaris in the 9th and 11th year of rotational grazing,showed a declining trend.and the three plant strains showed a trend of dwarfing and fragmentation.(2)In 4 rotational grazing intensity,the age structure of Stipa bungeana,Lespedeza davurica and Artemisia capillaris were juvenile,adult period>pre-old,old period,each species was a increasing population.The 11th year of rotational grazing Compared with the 6th year of rotational grazing,the growth rate of the young and adult plants of Stipa bungeana and Lespedeza davurica was larger,while the growth rate of the young and adult plants of Artemisia capillaris was the smallest;Plant grade ratios of 20-60 branches/plants of Stipa bungeana Plant grade ratios of 3—4 branches/plants of Lespedeza davurica and plant grade ratios of 0—30 branches/plants of Artemisia capillaris are LG and MG grassland>CK and HG grassland.It is indicated that the animals grazing under 2.67—5.33 SU/hm~2intensities is benefit for the growth and development of dominant plant populations in grasslands.(3)The contents of P and K of Stipa bungeana,Lespedeza davurica and Artemisia capillaris were juvenile>old;While the Fe content of Stipa bungeana was old>juvenile,and Cu and Mn contents of Artemisia capillaris were juvenile>old.The contents of ADF and NDF of Lespedeza davurica and Artemisia capillaris were highest at the old period,while the CP contents of Stipa bungeana and Lespedeza davurica were highest at the old period and their contents of WSC were highest at the juvenile period.The suitable grazing intensity of typical steppe in the study area based on the quantitative traits and age characteristics of dominant plant populations was 2.67—5.33 SU/hm~2.