Study On Key Ecological Thresholds Of Degraded Grassland Restoration In Shendong Mining Area

Coal mining in the Loess Plateau has aggravated the soil erosion and nutrient depletion of the regional ecosystem,resulting in ecological problems such as vegetation degradation and biodiversity reduction,making mining area a diffusion source of semi-arid grassland ecosystem degradation.By exploring the threshold effect in ecological restoration of degraded grassland,this study provides a theoretical basis for the refined restoration of large-scale degraded grassland,and provides new ideas and effective parameters for ecological restoration of mining areas.This study investigated the differences in soil properties,vegetation community,soil seed bank and soil microbes between the coal mining disturbance area and the undisturbed area in Shendong mining area.Then the impact of mining disturbance on the vegetation-soil-microbe system was analyzed,and determined that soil moisture,nitrogen and soil seed bank are important ecological factors that limit the regional ecological restoration.On this basis,the corresponding threshold experiments were carried out by controlling variables,and the range of water and nitrogen thresholds that could effectively promote vegetation restoration was determined,and the ecological threshold effects were comprehensively reflected from the three aspects of vegetation,soil and soil microbes.Then,through the structural equation model and the changes of the vegetation-soil-microbe system,the mechanism of the ecological threshold effect was explored,and the management measures and policy recommendations for applying the ecological threshold to the degraded ecosystem were summarized.The main findings are as follows:（1）Mining disturbances had negative effects on the vegetation and seed banks,soil and soil microbes.First,the number and density of aboveground vegetation and soil seed bank decreased in the mining disturbance zone,including 7 species such as Stipa bungeana and Artemisia scoparia,and reduced the similarity of soil seed bank and aboveground vegetation community.Second,the mining destroyed the soil structure,resulting in aggravated soil drought and desertification,decreased vegetation coverage and loss of soil nutrients,including organic carbon and total nitrogen.Third,Mining reduced the richness,uniformity and diversity of grassland soil microbial communities,but did not have a significant impact on dominant bacteria,including 11 phyla such as Actinobacteria and Proteobacteria,whose relative abundances exceeded 90%.（2）Appropriately increasing soil moisture and applying nitrogen fertilizer can effectively stimulate the ecological threshold effect,greatly increase the accumulation of vegetation biomass,and promote ecosystem restoration.First,when the soil moisture content increases to 12%,it has a significant stimulating effect on the improvement of plant growth and soil nutritional status,including plant biomass（increase by 109%）,chlorophyll content（increase by 22%）,soil total organic carbon（increase by 53%）and total nitrogen（increase by 28%）.Second,when the nitrogen application is 1 g N m^-2 yr^-1,it can significantly promote plant growth,including plant biomass（increased by 73%）,chlorophyll content（increased by 44%）,plant nitrogen content（increased by 1.5 times）.（3）The threshold effect of soil water and nitrogen is the result of joint action of plants,soil and microbes,and the threshold effect depends on the comprehensive effect of various factors in the ecosystem.First,the effect of water threshold is mainly due that the increase of soil moisture breaks the water limitation of plant growth to a certain extent,directly promotes the accumulation of plant biomass.And it also improves the utilization efficiency of soil nitrogen,which promotes the the absorption of nitrogen fertilizer by plants.Besides,it promotes catabolic activities such as the growth of bacterial communities and the secretion of extracellular enzymes,which accelerates soil material circulation and nutrient release,thereby promoting plant growth.Second,the effect of nitrogen threshold is mainly due to nitrogen fertilizer directly relieve the nitrogen stress of plant growth and promote plant growth in a short time,and by changing the population structure and quantitative characteristics of soil nitrogen cycle-related bacteria,thereby affecting the process of soil nitrogen cycle and soil nitrogen reserves,which realize a long-term path to promote the restoration of plant communities.（4）Based on the status quo of degraded grassland in Shendong mining area and the experimental results of ecological thresholds,the measures and suggestions for applying the concept of ecological thresholds to promote the restoration of degraded grassland ecosystems are summarized.First,develop ecosystem restoration plans based on ecological thresholds to achieve efficient ecological restoration with low economic costs and low ecological risks.Second,integrate the concept of ecological threshold into land management,and systematically promote and ensure similar types of ecological restoration of national land space from the land management level.Third,according to the actual resource endowment and restoration goals,flexibly select and adjust restoration measures,and ecological thresholds are pre-calibrated based on actual climate and soil conditions.There are 76 charts,15 tables and 152 references in this thesis.