| The desert steppe ecosystem is fragile and sensitive to the interference of human activities such as grazing and tourism.Therefore,exploring the impact of different utilization modes on the landscape pattern and soil quality of desert steppe is conducive to the scientific and rational utilization of grassland in semi-arid areas and reducing the risk of grassland degradation.In this study,the enclosed grassland,free grazing grassland and tourism grassland were taken as the research objects,and the methods of UAV image interpretation,field experiment and indoor analysis were used to study the landscape pattern distribution of grassland under different utilization modes,analyze the characteristics of vegetation diversity and stability,clarify the spatial variation law of soil nutrients,and clarify the spatial heterogeneity characteristics of soil water and the preferential movement process of water,The purpose is to reveal the influence mechanism of different utilization modes on desert steppe vegetation and soil,and provide a theoretical basis for the sustainable utilization of grassland in semi-arid areas.The main conclusions are as follows:(1)Desert steppe vegetation is micro patch distribution.There were significant differences in grassland landscape pattern under different utilization modes,and the landscape of free grazing area and tourism area tended to be fragmented and complex.The area of severe interference in the tourist area accounted for 53.82% higher than that in the enclosed area,which was generally at the level of severe interference;The area of severe disturbance in the free grazing area is 32.79% higher than that in the enclosed area,which is generally at the medium disturbance level.The landscape possible connectivity index(PC)and the proportion of patch area in the primary core area in the enclosed area were higher than those in the free grazing area and tourist area,and the landscape connectivity was significantly better than that in the free grazing area and tourist area.The results showed that the visible vegetation index(VDVI)of each area showed a global trend of aggregation,and the enclosed area was mainly "high-high" aggregation distribution,while the free grazing area and tourist area were mainly "low-low" aggregation distribution.(2)The grassland vegetation height,vegetation coverage,aboveground biomass and plant density in the enclosed area were significantly higher than those in the free grazing area and the tourist area.The number of dominant species such as Leymus chinensis in the free grazing area decreased,and the weed competitiveness improved.Simpson dominance index and Shannon Wiener diversity index were significantly higher than those in the enclosed area and tourist area.The stability of vegetation community was in the order of enclosure area>free grazing area>tourist area.The niche breadth of Stipa krylovii in free grazing area and tourist area decreased by 50.19% and 32.81% respectively compared with the enclosed area.There were significant differences in the average value of niche overlap among species under different utilization modes(P<0.05),which showed as free grazing area(0.51)>enclosed area(0.45)>tourist area(0.38).Plants in free grazing area ensured the survival of species and the relative number of organisms by increasing the niche overlap between species,and reduced the impact of grazing on the survival of plant species.(3)The vegetation coverage in free grazing areas and tourist areas decreased,and the risk of wind erosion and desertification increased,resulting in soil coarsening and nutrient impoverishment.Soil bulk density in free grazing area and tourist area was significantly higher than that in enclosed area;The total soil porosity decreased by 13.85% and 17.57%compared with the enclosed area,respectively;The sand content in the soil increased by5.74% and 17.01% respectively compared with the enclosed area.The contents of soil available potassium(AK),available phosphorus(AP),organic matter(SOM)and total carbon(TC)in the enclosed area were higher than those in the free grazing area and tourist area.The contents of total carbon,total nitrogen and the ratio of carbon to nitrogen in soil nutrient indexes showed weak variation characteristics(0.03～0.11),and the other indexes showed moderate variation characteristics,showing high heterogeneity.(4)The soil nutrient content has obvious spatial differentiation characteristics under different utilization modes.At 10 m × At 10 m scale,the spatial distribution of soil nutrients in the enclosure area mainly showed the patch structure characteristics of gradient distribution;The results showed that the free grazing area mainly showed the characteristics of speckled structure with poor connectivity;The tourist area shows obvious strip characteristics.The nugget coefficient [C0/(C0+C)] of soil nutrients in the enclosed area is between 20% and 77%,and the overall performance is moderate spatial correlation,which is affected by both structural factors and random factors.The nugget coefficient [C0/(C0+C)]of each index in the tourist area is greater than 75%,showing a low spatial correlation,which is strongly affected by random factors.There is a positive correlation between spatial heterogeneity of soil nutrients and species richness and diversity.(5)There are significant differences in the surface soil moisture content and spatial distribution of grasslands under different utilization methods.The soil moisture content in free grazing areas and tourist areas decreased by 30.22% and 67.75% compared to enclosed areas,respectively.The phenomenon of preferential flow occurs in all grasslands in the research area.Under the infiltration of 25 mm and 50 mm,the development of preferential flow in the enclosed area is significantly better than that in the free grazing area and tourist area.The staining area ratio of soil horizontal and vertical profiles decreases with increasing soil depth.When the infiltration water volume is 10 mm,matrix flow is the main flow in various areas.When the infiltration amount is 25 mm,the preferential flow velocity is about3-4 times that of the substrate flow.When the infiltration water volume is 50 mm,the maximum infiltration depth(Max D),staining area ratio(DC),and matrix flow depth(Uni Fr)of various areas all reach their maximum values.The root characteristics of vegetation and soil physical properties are the main influencing factors for preferential flow in desert grasslands.Soil bulk density,clay content,root length density,and root weight density are significantly correlated with the development of preferential flow. |
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