Characteristics Of Population Dynamics Of Artemisia Scoparia In Desert Steppe

The desert steppe is located at the edge of semi-arid and and regions.It is a typical type of steppe in the central area of Asia.It is also a fragile grassland ecosystem in the transition area from grassland to desert.In recent years,due to the lack of understanding of the structure and function of grassland ecosystem,and ignoring scientific management and irrational utilization of grassland resources,the Artemisia scoparia has become a main pioneer species and dominant species in Ningxia Desert Steppe owing to its strong adaptability to harsh environment,which has greatly inhibited other plant growth and led to decrease in quality of grassland for supplying forage.In Ningxia Desert Steppe,the zonal soil is sierozem soil,the non-zonal soil is sandy soil.There is also the exposed loose weathered base rock residual patchily distributed in this area.Natural rainfall is the main water source in this region.In Ningxia Desert Steppe,the annual rainfall is low,with an uneven spatial and temporal distribution,and the marked inter-annual fluctuation.This complex habitat,it is utmost important to keep up on the grassland resources dynamics,which would lay the foundation for the rational exploration and utilization of grassland,and the ecological environment protection.Therefore,A.scoparia was adopted as study object,grown in three kinds of soil types which were sandy soil,weathered base rock residual soil and sierozem soilin.Three rainfall treatments experiment was conducted,including normal rainfall plot increased-rainfall plot(increasing rainfall by 30%)and decreased-rainfall plot(decreasing rainfall by 30%)by using a self-made device equipped in the field.The effects of different soil types and changing precipitation on the population dynamics of A.scoparia were studied by the fixed-point sampling method.The main influencing factors of population dynamics of A.scoparia were analyzed.The main results are as follows:(1)The individual biomass accumulation of A.scoparia in Ningxia Desert Steppe was in accordance with the exponential growth.The relative growth rate of A.scoparia was Shuangfeng type in 2017.The time of occurrence was in May and early August,respectively.The relative growth rate showed a single peak in 2018,and the peak appeared in May.Relative growth rates of A.scoparia in sierozem soilt were lower in 2017,and the relative growth rates of A.scoparia in the three soil types was smaller in 2018.The precipitation had a relatively large effect on the growth of A.scoparia,while temperature was not the limiting factor for the growth of A.scoparia in this area.(2)The survival curve of.4.scoparia is similar to Deevey-I.It can be seen from the dynamic life table that there are a large number of seedlings of A.scoparia in the early stage.In the later period,the population density of A.scoparia has been greatly reduced,with an increasing mortality.In 2018,the number of A.scoparia populations in the three soil types was significantly higher than that in 2017.(3)There were significant differences in the number of the spring-germinated and autumn-germinated seedlings of A.scoparia between years.The number of spring-germinated seedlings in 2018 was more than that in 2017.While the opposite phenomenon was found for the ranking of number of autumn-germinated seedlings between the two years with less seedlings in autumn in 2018.The population of A.scoparia is higher in the habitat of sierozem soil.However,the canopy size,coverage rate and biomass of A.scoparia were relatively large in sandy soil habitats.Low the survival rate of A.scoparia population was recorded in the better water condition.The increase and decrease in precipitation had different effects on the morphological characteristics of A.scoparia,which had a greater impact on plant height and canopy size.(4)By analyzing the interaction effect of various factors on the growth indexes of A.scoparia,it was found that soil type significantly affected the growth indexes of A.scoparia.Precipitation treatment had a significant effect on the survival rate of A.scoparia.There was no significant interaction effect of year x soil type x precipitation treatment on the growth indexes.Among soil physical and chemical factors,water-soluble carbon had great influence on the survival rate and biomass of A.scoparia.