Responses Of Soil-Vegetation System To Wetland Drying Process In Mu Us Sandy Land

The paper studied the vegetation growth and diversity characteristics,soil physical characteristics,soil carbon,nitrogen and phosphorus nutrient composition,microbial community structure and metabolic function during wetland drying process,and analyzed the effects of soil moisture on soil and vegetation order and path,the main conclusions are as follows:?1?In wetland drying process,the aboveground biomass,density and coverage of vegetation showed a decreasing trend with the decrease of soil water content,while the vegetation richness index?R?and Shannon-Wiener diversity index?H?showed a trend of increasing first and then decreasing.The structural equation model?SEM?showed that soil moisture first affected vegetation coverage and biomass by driving changes in vegetation density.The reduction in soil moisture first reduced vegetation density,which in turn reduced vegetation coverage and biomass.The vegetation richness index and vegetation biomass in this study showed a"unimodal"relationship.In the first and middle periods of wetland drying process,the increase in the vegetation richness index is mainly driven by the decrease in vegetation density.?2?During wetland drying process,the soil bulk density and sand content showed trends of increasing and soil silt and clay contents showed a trend of decreasing,and soil pH showed a trend of first increasing and then decreasing.The results of the structural equation model show that soil moisture mainly affected the vegetation density by affecting the soil clay content,which in turn affected the vegetation biomass and coverage.The decrease of soil clay content and the increase of sand content were not conducive to the retention of moisture and nutrients in the soil,and are not conducive to the growth of vegetation roots,which in turn affected the growth of vegetation.In addition,the soil pH had a significantly negative correlation with the vegetation Shannon-Wiener diversity index?H?,but the relationship with the vegetation richness index was not clear.The relationship between soil pH and vegetation diversity in Mu Us wetland still needs further study.?3?In the wetland drying process,soil SOC,TN,ammonium nitrogen content,soil C:N ratio,C:P ratio and N:P ratio all showed a decreasing trend,while soil nitrate nitrogen content showed a trend of increasing.The soil TP content showed a trend of first decreasing and then increasing.The results showed that the most important driving path was:the reduction of soil moisture content driven the reduction of soil organic carbon and total nitrogen content,resulting in a decrease in vegetation density and biomass.Compared with total nitrogen,ammonium nitrogen and nitrate nitrogen,the effect of promoting vegetation growth is very small.The leaching of rain water leads to a low inorganic nitrogen content in the surface layer of Mu Us soil,which is statistically manifested as the small promotion effect of inorganic nitrogen on plants.For the relationship between vegetation diversity and soil nutrients,the analysis shows that there is a significant positive correlation between Shannon-Wiener diversity index?H?and soil SOC,TN,and ammonium nitrogen content,indicating that soil nutrient supply is important for maintaining vegetation ecology.The important role of system diversity.Compared with the Shannon-Wiener diversity index?H?,the vegetation richness index?R?is weakly affected by soil nutrition,which deserved further research.4)In this study,in wetland drying process,the soil MBC,MBN content,bacterial and fungal PLFA content all showed a continuous downward trend,while the ratio of MBC:MBN and fungus:bacteria continued to increase.Soil respiration and microbial metabolic quotients continued to rise in the middle and early stages of drought,but declined significantly in the later stages;while MBC:SOC maintained an upward trend during the process of wetland drought.The decrease of soil organic substrate during the wetland drought is the main reason for the decrease of soil MBC,MBN content,bacterial and fungal PLFA content.The increasing of soil MBC:MBN is not determined by the soil nutrient structure,but the change of microbial population.It is the increase of fungal content that caused the increase of soil MBC:MBN.In the process of wetland drought,the increase in the ratio of fungi to bacteria shows that the fungus has a stronger adaptability to the arid environment,and this adaptation may contribute to the continuous increase of soil MBC:SOC during the process of drought.In the first and middle periods of wetland drought,the improvement of soil aeration conditions promoted soil respiration;in addition,the improvement of soil aeration conditions,the reduction of soil clay and silt content,and the increase of the litter C:N ratio together promoted the rise of soil q CO₂.In the late period of drought,the lack of substrates led to a decrease in soil respiration and q CO₂.?5?Soil moisture promotes the growth of plants by increasing the contents of soil MBC,MBN,PLFA of bacteria and fungi,and fungi have the most important role in promoting vegetation biomass.The increase of soil microbial carbon,nitrogen,bacteria and fungi content also promoted the increase of vegetation diversity.By analyzing the effects of soil moisture on vegetation characteristics by driving clay particles,nutrient composition and microbial community structure,it was found that bacteria and fungi have a significant effect on vegetation diversity compared to soil particle composition and nutrient composition.It shows that during the process of wetland drought,the changes of soil moisture and soil nutrients mainly affect the diversity characteristics of vegetation by promoting soil microorganisms.