Study On The Response Of Typical Vegetation To Changes In Soil Water-Groundwater In The Sandy Area Of Yulin

Soil water is an important component of the hydrological cycle in terrestrial ecosystems,and as the hub of the hydraulic connection between groundwater and surface vegetation,its spatial and temporal dynamic distribution plays an extremely important role in the sustainable construction and management of vegetation in drylands.Therefore,to elucidate the spatial and temporal dynamics of soil water in typical vegetation in dryland areas,to clarify the relationship between vegetation-soil water-groundwater system balance and the response mechanism of hydro-ecological effects,can provide a basis for the formulation of vegetation construction and restoration measures.In this paper,we set up a test site in the Yulin sand area at the southeastern edge of the Mu Us desert,and used five typical sand-fixing plants,namely Salix psammiphlia,Artemisia ordosica Krasch,Amorpha fruticosa,Caragana korshinskii Kom,Pinus sylvestris var.mongholica Litv as research objects.The spatial representation of vegetation under the control of the soil-water-groundwater system was analysed by obtaining different data on groundwater table depth(GTD),soil moisture,vegetation cover and elevation,exploring the multi-scale spatial response of vegetation to changes in the soil-water-groundwater system,and further delineating vegetation cover and dominant vegetation species interval categories.The main findings are as follows:(1)Soil moisture of typical vegetation in the study area was characterized by significant heterogeneous variability at spatial and temporal scales.In the spatial scale,the results on the vertical profile showed that the surface variation was significantly greater than the deeper characteristics,and the spatial dependence and aggregation characteristics gradually weakened with the increase of soil depth,and the degree of spatial autocorrelation also decreased;in the radial direction,it showed obvious "dry" and "wet In the radial direction,there are obvious "dry" and "wet" island effects,and there are "water drying and enrichment areas" around the main root zone of vegetation.In the time scale,soil moisture variation in the root zone of vegetation showed three obvious periods of depletion(April to June),recovery(June to July)and stability(July to August),and the spatial pattern of soil moisture in the deep layer under different vegetation cover was more stable than that in the surface soil.(2)Like soil moisture,the root distribution and soil particle size composition of typical plants also have obvious spatial variability characteristics.Among them,the root system of typical plants has a bimodal feature in the vertical direction and an exponential decreasing trend with increasing radial distance in the horizontal direction.Soil particle composition was dominated by sand grains,accounting for 83.28%～99.98%,mostly concentrated in 50～250μm,with fine and medium sand as the dominant grain classes.In the vertical direction,soil grain size distribution was more uniform for Artemisia ordosica,Caragana korshinskii and Pinus sylvestris var.mongholica Litv,while the difference in grain size among vegetation in the horizontal direction was not significant(P < 0.05).(3)Environmental factors affecting soil moisture variability in each profile of the vegetation root zone differed between wet and dry periods.During the wet period,typical vegetation vertical soil moisture was positively correlated(P < 0.05)with the content of vegetation root system and powder grain fraction,negatively correlated(P < 0.05)with sand and coarse sand fraction in the soil,and randomly positively or negatively correlated with very fine sand;soil moisture variation was mainly influenced by powder grain and very fine sand grain,and the maximum contribution could reach 75.3% and 69.3%,while in the dry period,vegetation roots were negatively correlated with soil moisture(P < 0.05)and the maximum contribution(68.5%)during the dry period.Compared to the vertical direction,the environmental changes in the vegetation root zone had a weaker effect on soil moisture in the horizontal direction,and the soil moisture variation was mainly controlled by the chalky sand and medium,coarse,and very fine sand fractions in the soil texture.(4)Under the control of the soil water-groundwater system,the vegetation communities in the study area exhibited obvious zonal distribution characteristics in space.The response mechanisms of vegetation to the soil water-groundwater system differed between the natural succession-dominated area and the artificial restoration area.In the natural succession area(GTD < 5 m),soil water content was significantly and positively correlated with vegetation cover(path coefficient of 0.68,P < 0.001),while both were significantly and negatively correlated in the artificial restoration area(GTD > 5 m)(path coefficient of-0.43,P < 0.01),and the increase in cover responded strongly to soil water content.In summary,the following vegetation restoration strategies were proposed under each interval scale category.The outer zone(GTD 5～15 m)and the edge zone(GTD 10～15 m)need more drought-tolerant shrubs and grasses.