| Vegetation restoration is widely used as an important measure to control surface soil erosion,which plays an important role in promoting soil development,improving soil characteristics,improving soil fertility and improving regional ecosystem function.The special geological structure in karst area,the natural conditions are fragile,the slow speed of soil formation leads to the shortage of soil resources,and the soil nutrients with poor stability are easily lost.Once the surface vegetation was destroyed,a large amount of soil and water loss will lead to the formation and expansion of rocky desertification,and then aggravate the deterioration of the ecological environment.This problem needs to be solved urgently.In this study,the content and distribution characteristics of soil nutrients and heavy metals in different landforms（non-karst landforms,karst landforms and vegetation restoration landforms）were studied by spatio-temporal substitution method in Guizhou Caohai Nature Reserve（2171.7 m above sea level）.Focus on the following three aspects of work:（1）the differences and influencing factors of soil nutrient cycling process in different geomorphological environments.（2）the differences and influencing factors of heavy metals in different geomorphological environments;（3）the synergistic effect of soil-plant and its microbial effect in the process of vegetation restoration in karst area.The main results were as follows:（1）the content of soil organic carbon in non-karst landform is significantly higher than that in karst landform,and the content of each carbon component decreases gradually with the increase of depth,and showed the phenomenon of enrichment in the surface layer.In the initial stage of vegetation restoration,the content of soil organic carbon did not follow a steady upward trend,and fluctuated.The combined effects of the rapid expansion of vegetation community and the carbon retention and carbon loss caused by microorganisms lead to the difference of soil carbon components between the vegetation restoration belt and the karst zone.In addition,the increase of active nitrogen in the vegetation restoration belt may be an important reason for limiting carbon input and affecting soil organic carbon.（2）Compared with the non-karst belt,the soil nitrogen accumulation of the former showed the law of upward enrichment,which was basically consistent with the distribution trend of organic carbon,and the contents of soil total nitrogen,nitrate nitrogen and ammonium nitrogen were higher than those in the karst zone.Ammonium nitrogen accounts for the main part of inorganic nitrogen.The karst belt is affected by the coupling structure of soil-surface karst zone,vegetation types and litter,and the soil nitrogen accumulation rate is significantly different from that of the non-karst zone.Because of the low vegetation coverage and less litter return,the organic carbon available to microorganisms is lower,and soil erosion will weaken soil carbon accumulation,so it is difficult to accumulate soil nitrogen.In the initial stage of vegetation restoration,the nitrogen retention and supply intensity（especially the content of nitrate nitrogen and ammonium nitrogen）in soil will be improved to a certain extent,and the soil erosion will be weakened.the contents of soil nitrate and ammonium nitrogen were significantly higher than those in the karst zone.（3）The soil phosphorus content in the non-karst zone was significantly lower than that in the karst zone,and the former decreased gradually with the increase of depth,while the karst zone did not show this phenomenon.The change of total phosphorus and available phosphorus content in soil is mainly affected by vegetation community,and the change of soil total phosphorus and available phosphorus content in mountain area is also affected by soil organic matter,p H value,climatic conditions and other factors.at the initial stage of vegetation restoration,the content of soil phosphorus increased gradually,and the content of total phosphorus gradually tended to be the same as that of non-karst zone,while the content of available phosphorus fluctuated greatly.The rapid expansion of vegetation community and the joint action of microorganisms make the composition of soil phosphorus in the vegetation restoration belt different from that in the karst zone.（4）The contents of Cr,Ni,Zn,As and Pb in Caohai area did not exceed the background value of soil heavy metals in Guizhou province,and the non-karst sample zone showed the distribution characteristics of surface enrichment and bottom precipitation enrichment of soil heavy metals.Path analysis showed that non-metallic soil factors such as soil bulk density,total nitrogen and ammonium nitrogen had a direct effect on the content of heavy metals in soil.Vegetation restoration effectively restored carbon,nitrogen and other nutrient elements in the soil,enhanced the soil material cycle,and made the content of heavy metals in the surface layer of soil higher than that in 10-20 cm soil layer.Plant absorption,microbial biosorption mechanism,root exudation coupling and the dissolution of soil soluble organic carbon and p H made the contents of heavy metals Cr,Ni and Pb in vegetation restoration sample belt decreased slightly compared with karst soil.At the same time,affected by vegetation coverage,residual heavy metals in soil are further leached by surface runoff.（5）The vegetation community changed before and after vegetation restoration,but the bacterial community and diversity did not change significantly.Through the comparison of the richness of actinomycetes and Proteus in vegetation restoration and karst soil,it was found that the bacterial richness of actinomycetes in vegetation restoration soil was slightly higher than that in karst soil,while that of Proteus was slightly lower than that in karst soil.it showed that vegetation restoration does promote the accumulation of soil nutrients.Soil p H,organic carbon and oxidizable organic carbon significantly affected the community structure of soil fungi.Organic carbon and oxidizable organic carbon significantly affected basidiomycetes and ascomycetes in karst soils.Soil p H significantly affected basidiomycetes and ascomycetes in vegetation remediation soils,and there was no significant difference in soil fungal diversity and abundance,except for vegetation types and soil properties.The short time of vegetation restoration was also one of the important reasons. |
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