Succession Characteristics Of Re-vegetation Community And Dynamics Of Soil Nutrients In Open-pit Coal Mine In Typical Steppe

Grassland ecosystems play an important role in maintaining soil and water conservation,regulating carbon sinks,providing services,and maintaining biodiversity.However,open-pit coal mining on grasslands can cause lots of serious ecological and environmental problems in some areas,resulting in the loss of grassland ecological functions.Especially the large number of dump sites formed by open-pit coal mining,which had been exposed surfaces outside,causing frequently geological disasters,leading to severe soil erosion,and polluting grassland environment.Those were attracted more and more attention.In recent decades,research on vegetation reconstruction,landform reshaping,ecological restoration,and land reclamation in open-pit coal mines in China has been continuously deepening.However,in the practice of re-vegetation and ecological restoration process,there are still existing problems,such as poor competitiveness of plant,low survival rate,unstable communities,improper selection of surface cover,and severe surface soil erosion in open-pit coal mine dump sites.In order to clarify the evolution law of plant community and soil nutrients for the reconstruction of open-pit coal mine dump in grassland area,and the impact of runoff and environmental factors on plants and soil,a permanent research site was established in 2007 at different parts of dump in Shengli West open-pit coal mine and Wulantuga open-pit coal mine in Xilinhot City,Inner Mongolia Autonomous Region.Conducted research on re-vegetation community and succession.After planting multiple plants on the slope of the experimental area,such as biological-fence and biological-barrier coverage treatments were adopted for protection,with no surface cover as the control group.Randomly set up observation areas and quadrats on the slope,in the middle and under the slope,and on the flat plate.During the 2009 to2020,fixed point observation and sampling were conducted on the plants and soil in the experimental site,continuous monitoring of the soil and plant communities.In 2016,a set of runoff devices were installed on the slope of the experimental area to observe the topsoil erosion,and to study the relationship between soil organic matter,nutrient accumulation and surface cover of vegetation.Based on the principles of ecology and restoration ecology,quantitative ecology and statistics methods were used to analyze the succession law of plant communities,soil nutrient dynamic,surface runoff and climate factors of the reconstructed plant community,systematically clarify the structural characteristics and evolution law of the reconstructed plant community in the open-pit coal mine waste dump,exploring the driving factors affecting slope runoff and soil nutrient loss,and reveal the impact of long-term ecological restoration on plant community and soil nutrients of open-pit coal mines in typical steppe in Inner Mongolia.The main results were showed:（1）After 13 years of plant cultivation,there were a total of 46 species of plants in the experimental site of dump,including 14 families and 33 genera.Compared with the control group,the number of plant species composition,community height,community coverage,and community density under the two coverage treatments all significantly increased.At the initial stage of re-vegetation,the plant community was dominated by artificially sown plants,with the important value accounting for 96%.After 5 years of planting,the important value of artificially sown plants decreased to 54%,a large number of annual and biennial miscellaneous grasses and the advantageous plants of the grasslands,such as Stipa grandis,Leymus chinensis,and Agropyron cristatum,had begun to appear.After 8 years of planting,the important value of manually sown plants accounted for 31%,dominated by manually sown shrubs,semi shrubs,and naturally invasive annual plants.After 13 years of planting,the important value of artificially sown plants accounts for 39%,plant community dominanted by artificially sown shrubs and semi shrubs,naturally invaded annual plants and perennial plants.（2）After planting for 2-13 years,the diversity index and stability coefficient of the community fluctuated,the Shannon-Weiner index and Simpson index showed a single peak fluctuation upward trend,while Margalef richness index showed a double peak fluctuation downward trend.The Pielou evenness index showed decreased first and then increased,while the functional richness index and functional evenness index showed a single peak upward trend.The FDiv,Rao Q,and ICV show a decreasing trend.For the Shannon-Weiner index,the two coverage treatments were consistently significantly higher than the control group.For the Simpson index,in the 11^thyear of planting,there was no significant difference among the two coverage treatments and the control group,while there was a significant difference in other years.For Margalef richness,the two coverage treatments in the second year of planting were significantly lower than the control group,and significantly higher in other years than the control group.For the Pielou evenness index,there was no significant difference between the treatments in the second year of planting.In other years,the biological barrier coverage treatment was significantly higher than the other two treatments.For the functional diversity index,there was no significant difference among the treatments after 2 years of planting,while the two coverage treatments in other years were significantly higher than the control group.For the ICV,there was no significant difference among the treatments in the second year of planting,while the biological-fence coverage treatment in other years was significantly higher than the other two treatments.（3）In the second year of planting,there was no significant difference in above-ground biomass between the two coverage treatments and the control group.during the second to13^thyears of planting,the two coverage treatments were significantly higher than the control group.Planting for 2-13 years,the above-ground biomass of artificially sown plants was significantly higher than that of naturally invasive plants.The above-ground biomass of the two coverage treatments and the control group increased year by year after planting for 2-9 and 11-13 years,with significant differences between years.After planting for 2-13 years,the under-ground biomass of the two coverage treatments was significantly higher than that of the control group,and the above-ground biomass increased year by year,with significant differences between years.For 2-9 and 11-13 years of planting,the root content of 0-10 cm soil depth was significantly higher than that of 10-20 cm and 20-30 cm depth.In the 10^thyear of planting,the root content of 10-20 cm was significantly higher than that of 0-10 cm and 20-30 cm depth.（4）After 13 years of planting,the soil organic matter,total nitrogen,available phosphorus,and total potassium contents under the two coverage treatments were significantly higher than those in the control group,and the soil p H value was significantly lower than that in the control group.During the planting period of 2-13,the content of soil organic matter,total nitrogen,available phosphorus,and soil p H decreased year by year,with significant differences between years.There was no significant interannual difference in changes in soil total potassium content.There was a significant positive correlation between soil organic matter and soil total nitrogen,species number,and community coverage.There was a significant positive correlation between soil total nitrogen and richness index,community coverage,stability coefficient,and root content.The content of soil available phosphorus and total potassium has no significant correlation with many indicators of plant community,and is not a limiting factor for plant growth.（5）During the planting period of 9-13 years,the ersoion of the surface slope dump covered with biological-fence was significantly lower than that of the treatment with biological-barriers,and significantly lower than that of the control group.There was also a significant difference between the treatment with biological-barriers and the control group.The net flow on the slope was significantly negatively correlated with the content of soil organic matter,total nitrogen and available phosphorus,and with the above-ground biomass and under-ground biomass of the plant community.There was a significant positive correlation between slope runoff and rainfall,with no significant interannual variation.