The Effect Of Coal Mining Subsidence On Soil Properties And Bacterial Community Structure In The West Aeolian Sand Area

Coal is one of China's major energy sources and accounts for 70 percent of the energy use.Meanwhile,coal mining had broken the balance of ecological environment and caused a series of ecological and environmental problem,for example,strip mining would lead to the damage of soil and vegetation,underground coal mining would cause soil collapse and ground fissures,vegetation damaged and soil sandy desertification.The Shendong mining area is one of the important strategic energy bases of China,located in Shanxi,Shannxi and Inner Mongolia provinces at the junction,along the south margin of the Mu Us desert in the north of the Loess Plateau.The ecological environment is fragile with semi-arid climate,the soils were covered by aeolian sandy soil from a depth of 5-50 meters resulted from strong wind every year.Underground mining was the main coal-mining way and the coal output was about 95 percent of total output.Therefore,land subsidence became one of the main disasters,seriously destroyed the land resources and the area of land subsidence has been increasing at a rate of about 200 hm² per year.In addition,soill structure might destroy and caused groundwater level fell,soil moisture and nutrient serious lost,soil enzyme activities decreased,soil microbial communities and population reduced and biological diversity destroyed.So far,most studies had focused on the effect of land subsidence on soil physiochemical properties and vegetation,while little research has been conducted on soil microbial microbial community and the effect of underground coal mining on soil microbial microbial community in west aeolian sandy area.In particular,soil microbial communities play an important role in the whole ecosystem by promoting nutrition circulation and litter decomposition.In addition,soil bacteria are very sensitive to changes in the environment and could be cited as an indicator reflecting changes in soil quality.Here,we investigated soil properties and soil bacterial communities at depth of 0-180 cm in an unexploited area and a land subsidence area of Shendong coal mining for 1.5 years of follow-up research,and determined the effect of land subsidence on soil bacterial communities,Characteristic of spatiotemporal variations of soil properties,the succession of soil microbial community,energy metabolic functions and the response of bacterial communities to changes in the soil environment.These results provide theoretic foundation for management and restoration of land subsidence.The main results obtained are as follows:1.Land subsidence made the soil quality decline mainly in many ways,such as the pH,water content,electric conductivity,organic matter,organic carbon,total carbon,total nitrogen,available potassium,available phosphorus,ammonium nitrogen and nitrate nitrogen at topsoil in uniform subsidence and heterogeneous subsidence area were significantly decreased.When 2 years after land subsidence,the difference of soil properties between control area and subsidence area was gradually decreased,suggested that soil quality is on their way to be recovered.2.Land subsidence significantly decreased the activity of urease,phosphatase and sucrase of topsoil.When land subsidence time was prolonged,the difference of urease,phosphatase,sucrose and catalase of 0-180 soil layers between control area and subsidence area was gradually decreased,indicated that the soil enzyme activities represented self-healing capability.3.Land subsidence caused the change of vertical distribution of soil physicochemical properties.For example,the total nitrogen content was decreased in the order 20 cm>100 cm>180 cm in control area,while that in uniform subsidence area and heterogeneous subsidence area were decreased in the order 100 cm>180 cm>20 cm;the available potassium content was decreased in the order 20 cm>100 cm>180 cm in control area,while that in uniform subsidence area and heterogeneous subsidence area were decreased in the order 180 cm>100 cm>20 cm;When land subsidence time was prolonged,the difference of total nitrogen,available potassium,available phosphorus content of deep soil layers between control area and subsidence area was greater than that of topsoil,the difference of soil water content,total carbon,total nitrogen and available phosphorus between control area and heterogeneous subsidence area was greater than that between control area and uniform subsidence area,suggested that land subsidence had greater effect on soil properties of deep soil layers than topsoil and had greater effect on soil properties of heterogeneous subsidence area than uniform subsidence area.The vertical distribution of activity of urease,phosphatase,sucrase and catalase in control area and uniform subsidence was decreased in the order 20 cm>100 cm>180 cm after land subsidence by 1.5 years.Also,there was a relationship between soil properties and soil enzyme activities.The pH and water content were significant correlated with soil enzyme activities,and the soil enzyme activities were significant correlated with soil nutrient content.4.At the phylum level,the soil in west aeolian sand area were dominant by Proteobacteria,Actinobacteria,Acidobacteria,Firmicutes and Bacteroidetes.At the genus level,the core genera were Pseudomonas,Nocardioides,Arthrobacter,Rhizobium,Sphingomonas,Gp4,Gp6,Gp16,land subsidence significantly changed the soil bacteria community structure.The bacterial community in both control and uniform subsidence area were dominant by Pseudomonas,Nocardioides,Hydrogenophaga,Arthrobacter,Marmoricola,Rhodococcus,Rhizobium and Gp6after land subsidence by 1.5 years.The bacterial community were dominant by Pseudomonas,Gp6,Gp4,Gaiella,Rhizobium,Gemmatimonas,Arthrobacter and Gp16 after land subsidence by 2 years.The bacterial community were dominant by Pseudomonas,Arthrobacter,Gp6,Gaiella,Gp16,Gemmatimonas,Gp4 and Hydrogenophaga after land subsidence by 2.5 years.When land subsidence time was prolonged,the relative abundance of some bacteria which could promote soil fertility and nutrient recycling were increased,such as Pseudomonas,Gemmatimonas and Arthrobacter.5.The change of climate could affect soil bacterial richness and diversity.In the process of seasonal change,the Chao indices and Shannon indices of 0-180 cm soil in control area were gradually increased,indicated that soil bacterial species richness and community diversity were the highest in spring and the lowest in summer.The seasonal variations of 0-180 cm soil in uniform subsidence area was consistent with that in control area.Furthermore,land subsidence changed the bacterial richness and diversity at the depth of 0-180 cm soil,in winter and spring,the bacterial richness and diversity at the depth of 0-180 cm soil in subsidence area were lower than that in control area,while due to the special climate of summer,the bacterial richness at the depth of 20 and 180 cm soil in subsidence area was higher than that in control area,and the bacterial diversity at the depth of 180 cm soil in subsidence area was higher.As showed in pca,venn and heatmap,when land subsidence time was prolonged,the difference of soil bacterial richness and diversity between control area and uniform subsidence area tended to be slight which represented that the soil microbial richness and diversity had the ability to be self-healing.6.Land subsidence decreased the carbon metabolism,nitrogen metabolism and sulfur metabolism.In addition,when land subsidence time was prolonged,the difference of bacterial energy metabolic ability of 0-180 cm soil between uniform subsidence area and control area tends to be slight,the results showed that soil bacterial energy metabolic had the ability to be recovered.7.In the west aeolian sand area,the soil variables which could affect soil bacterial community structure was water content,pH,electrical conductivity,NO₃^--N,organic matter and available potassium.The main soil variable driving changes of soil bacterial community structure were NO₃^--N,soil moisture and pH after land subsidence by 1.5 years,2 years and 2.5 years.