Study On The Plant-Soil Interaction During The Degradation Of Alpine Meadow In Three-River Headwaters Region Of China

In recent decades,due to the combined effects of environmental changes and human activities,there has been degradation of alpine grasslands in the Three-River Headwaters Region,and some areas have even degraded into bare "black-soil beaches".Therefore,it is necessary to conduct in-depth research on these degraded alpine grasslands to explain their degradation and succession processes and driving mechanisms.This study took the most widely distributed alpine meadow in the ThreeRiver-Source region as the research object.Based on field investigation sampling and indoor sample analysis data,we explored the changes in plant community and soil physicochemical characteristics during the degradation process of alpine meadow in the region.We also studied the direct and indirect effects of plant community indicators and soil physicochemical factors based on the partial least squares path models(PLS-PM),revealing their changing patterns and underlying mechanisms.The main conclusions are as follows:(1)As the degree of degradation increases,the coverage and aboveground biomass of alpine meadow plant communities gradually decrease,while the importance value of forbs shows an overall upward trend.The Gleason richness index of plant communities is highest(1.63)in the light degradation stage and lowest(1.26)in the severe degradation stage.Although the diversity indices of plant communities in alpine meadows at different stages of degradation show little difference,the evenness index of plant communities shows a significant increase with the degree of degradation.(2)The soil bulk density of alpine meadows gradually increases with the degree of degradation,while the soil moisture content in the 0-5cm soil layer decreases with the degree of degradation.The total nitrogen and organic matter content of the soil both show a significant decreasing trend with the degree of degradation.The content of soil organic matter and total nitrogen in the 0-5cm soil layer is generally higher than that in the 5-10 cm soil layer for alpine meadows at all five stages of degradation.However,with the degree of degradation increasing,the difference in soil organic matter and total nitrogen content between the 0-5cm and 5-10 cm soil layers gradually decreases,and even levels off.The total phosphorus content in the soil also shows a decreasing trend during the degradation of alpine meadows,but the trend is not as obvious as that of soil total nitrogen and organic matter.The change in soil p H is generally small,and the soil electrical conductivity in the 0-5cm soil layer is significantly higher than that in the 5-10 cm soil layer.(3)By constructing a partial least squares path model,we investigated the plantsoil interactions in alpine meadows at different stages of degradation in the ThreeRiver-Source region.The results showed that as the degree of degradation increased,the plant-soil interactions in alpine meadows gradually weakened.The plant community in undegraded alpine meadows had a negative interaction with soil nutrients,while the soil nutrients in degraded alpine meadows had a positive effect on the diversity of plant communities,but at the same time,had a negative effect on plant growth.The plant diversity in native alpine meadows indirectly had a positive effect on soil nutrients(path coefficient = 0.28),while the diversity of plant communities in moderately,severely,and extremely degraded alpine meadows also had a positive effect on soil nutrients.The importance value of forbs in undegraded and moderately degraded alpine meadows had a negative effect on soil nutrients,while the plant communities in mildly,moderately,and severely degraded alpine meadows had a strong positive effect on the physical properties of soil(path coefficient = 0.4993,0.3139,0.5608).The soil physical properties of alpine meadows at all four stages of degradation had a positive effect on the growth of plant communities.In conclusion,during the degradation process of alpine meadows in the ThreeRiver-Headwaters region,there are interactions between plants and soil,and the interaction between plants and soil at different stages of degradation is also different.This indicates that in the protection and restoration of alpine meadow ecosystems,comprehensive management of plants and soil needs to be considered to promote plantsoil synergies,slow down the degradation of meadow soil,and improve the stability and sustainability of the ecosystem.In addition,it is necessary to strengthen the indepth study of the plant-soil interactions in alpine meadows at different stages of degradation in order to develop more effective meadow protection and restoration strategies.