Water Source Of Shrubs And Herbs Vegetation Of Artificial Caragana Intermedia Shrublands In Desert Steppe

Soil drought is the main problem of maintain ecosystem stability of artificial Caragana intermedia shrublands in desert steppe area.It is important to clarify the water source of dominant shrubs and herbs of Caragana intermedia shrublands,which has important theoretical and application research value for adaptive management and innovation of degraded Caragana intermedia shrublands.BSC is a typical habitat characteristic of the aging Caragana intermedia shrublands(Planted in 1975a),and it tend to have a significant effect on the water circulation of system.In order to explore the water source of the shrubs and herbs vegetation,especially the water use of the aging Caragana intermedia shrublands,and the effects of the biological soil crust on the water source and correlation of the shrubs and herbs,we take three different age stages include 1975a,1987a and 1996a of Caragana intermedia as the object of study in Yanchi County.Based on the analysis of evolution pattern of soil and vegetation of artificial Caragana intermedia shrublands,we analyze and compare the differences of the water sources of the aging Caragana intermedia shrublands and other age stages Caragana intermedia.Then we focus on the role of biological soil crust in the water source of aging Caragana intermedia shrublands of shrubs and herbs.The main conclusions are as follows:(1)Evolution Patterns and driving of soil and vegetation of artificial Caragana intermedia shrublands:Compared with natural grassland,after the number of species of Caragana intermedia shrublands of 1996a reached the peak value,and the number of species decreased gradually with the increase of age,perennial gramineae grass began to appear.However,the dominant species was the annual vegetation still.The species diversity index showed a trend of decreasing after increasing first.The main indexes of soil nutrient was significantly restored after introduction artificial Caragana intermedia shrublands to the grassland of degraded grassland,and maintained a positive recovery trend in the study period.But the natural decay of Caragana intermedia shrublands and the sudden increase of some soil indexes occur simultaneously.The full development of biological soil crust promoted the improvement of soil quality in the aging Caragana intermedia shrublands,and also changed the soil hydrological process and hydrological environment characteristics of Caragana intermedia shrublands.For the internal succession of artificial Caragana intermedia shrublands,the evolution of desertification environment dominated by early Caragana intermedia shrublands was gradually transitioned to the succession stage of ecological and hydrological mutual feedback driven by later biological soil crust.(2)Comparison of water source of Caragana intermedia shrublands in different ages:The soil water use efficiency of internal of Caragana intermedia shrublands on the surface soil layer decreased gradually with the increase of age,and the water use efficiency of deep soil was gradually increased.There was no significant difference between the water use efficiency of 1996a and 1987a Caragana intermedia shrublands on the inside and outside of soil layer.The rate of water use efficiency at external of 1975a Caragana intermedia shrublands,in the 0-5cm soil layer was higher than 0-10cm soil layer of external of 1996a and 1987a,and higher than 0-10cm soil layer at internal of 1975a Caragana intermedia shrublands,but the rate of water use efficiency below 10cm soil layer was less than 1987a.With the increase of age,the rate of water use efficiency of deep soil moisture increased,and the rate of water use efficiency was 1996a(16.0%)<1987a(30%)<1975a(33.6%).In general,with the increase of age,Caragana intermedia shrublands tend to use the deep soil moisture.Internal of Caragana intermedia was higher than external of Caragana intermedia,in addition to the surface layer,which reveals the potential role of biological soil crust in the water source of aging Caragana intermedia shrublands.(3)The change of water source and competitive relationship of dominant shrubs and herbs with growing age:the water source of the annual herbaceous in different age was mainly concentrated in the surface layer of 0-l0cm,which is represented by Artemisia scoparia and Bassia dasyphylla;With the increasing of age,the rate of water use efficiency of Artemisia scoparia further improved,and from internal of Caragana intermedia>external of Caragana intermedia to internal of Caragana intermedia<external of Caragana intermedia.On the whole,with the increasing of age,the vertical soil differentiation of the water source of the dominant shrubs increased and the competition was weakened.The emergence of biological soil crust changed the tendency of changes in the water competition pattern of shrubs on the local space:the enhancement of water use(17.1%;or even higher than Artemisia scoparia,12.7%)of on the crust(0-5cm),around improve of water conditions in BSC of the external of Caragana intermedia,strengthened the water competition of 0-5cm soil.(4)Dynamic change of the water source of shrubs and herbs in aging Caragana intermedia shrublands:In the dry season,the moisture content of Caragana intermedia shrublands is concentrated in the B layer(46.65%),which showed relatively uniform or relative concentration.Artemisia scoparia were concentrated on the A layer(47%)and the B layer(26%).In the rainy season,the soil water conditions were significantly improved.Caragana intermedia shrublands is still use the biological soil crust water,and the average utilization rate was 22.7%.B layer is still the main water source of Caragana intermedia water source,and the rate of water use efficiency of D layer was more stable.But the variation degree of C layer was the higher;The water source of Artemisia scoparia was further concentration,which increased and extended to B layer and C.The contribution of A layer was decreased significantly.With the extension of precipitation process,rate of water use efficiency was increased from 3.4%to 34.1%.The B layer was still the concentrated layer of water competition,but the water source structure and dynamic were significantly different.During the period of relatively stable,soil moisture at the end of the growing season,the water source structure of Caragana intermedia shrublands was similar to the early dry season.The results of the experiment in 2015-2016 were summarized,compared with Artemisia scoparia(rate of water use efficiency of A layer was 16%,range of 5-47.2,coefficient of variation of 97.79%,above 15%of the frequency occupied only 1/6),biological Soil moisture(rate of water use efficiency was 20.67%,range of 7.2%-42.6%,coefficient of variation was 52.47%)is not negligible in the composition of the whole water source of Caragana intermedia shrublands.Therefore,the biological soil crust is an important and relatively stable potential water source of Caragana intermedia.In terms of the use of the two vegetation for the biological soil crust,the soil water use behavior of aging Caragana intermedia shrublands performanced like to the short-lived herbaceous plants on the surface soil.(5)The conditions and mechanism of aging Caragana intermedia shrublands using the water of biological soils:the distribution of fine roots and the availability of water are two key conditions for determining whether the aging Caragana intermedia can be used and the extent to BSC or not.The results showed that,there are obvious gradations intensitied in the root system of Caragana intermedia shrublands.In the 0-100cm soil layer,the fine root intensity(0.307)of the upper layer(0-40cm)is much higher than the lower layer(60-100cm)(0.078);In the 0-10cm soil layer,the total root weight of the fine root of 0-5cm was significantly higher than 5-10cm.Compared with no crust treatment,in the dry season,the soil moisture fluctuation of 0-5cm soil surface was significantly reduced,and the stable humidity increased significantly(the bottom value was 7-8%and the platform stage was short),and the water environment in the crust was obvious,which is better than that of the lower soil in the whole dry season;However,the relative holding water effect of the crust in the rainy season is weakened or even lost;The relatively high and stable water condition of the BSC in the dry season induced the reverse growth of the fine root of Caragana intermedia shrublands,and also explained the use of BSC water after the soil moisture environment is improved in rainy season.Shading experiments also validated the above conclusions.As a deep-root and perennial leguminous shrubs,the aging of Caragana intermedia shrublands showed that the water use strategy was utilize surface and deep soil moisture at the same time.The positive relationship mechanism between biological soil crust and aging Caragana intermedia,provide a new research ideas for eco-hydrological mutual feedback mechanism of maintain the stability of deep-rooted shrubs in arid areas.