The Movement Law Of Soil Water Around Mining Ground Fissures And The Mechanism Of Microbial Remediation On Root Damage

Taking into account the ecological environment protection while developing coal resources,is an important strategy for China to achieve sustainable development.China is a country with abundant coal resources.While a large amount of coal mining brings economic benefits,it also has serious negative effects.For example,coal mining can cause surface subsidence,deformation,and generate ground fissures,which not only cause damage to ground buildings,roads,agricultural facilities,but also disturb the surface soil properties and vegetation growth.However,the effect of ground fissures on soil water movement is still unclear,and there are no enough quantitative results that can reflect the relationship between the three-dimensional morphology of the fissures and their ecological effects.In addition,the effects of fissure induced root damage stress on plant growth and whether bioremediation can alleviate fissure induced root damage stress,all of these points need to be studied.This paper studied the above scientific issues through a combination of field monitoring and indoor remediation mechanism research,revealed the mechanism of ground fissures effects on plants growth and soil water movement,and explored the mechanism of microbial remediation on root damaged plants.In this study,we first studied the mining subsidence ground fissures under two different topography in the southern wing aeolian sand area and northern wing loess gully area of the Nantiaota mine.The changes of soil water around fissures,and the roots and shoot growth of dominant species were monitored.The effects of fissures on soil water and the effects of fissure induced root damage stress on plant growth were studied.In order to further study the mechanism of the effect of fissures on soil water and plants with the exclusion of complex environmental variables,ground fissure simulation devices were designed,methods to obtain the three-dimensional morphology of fissures were explored,and the characteristics of the effects of fissures on the spatial and temporal distribution of soil water were studied.And also,the Hydrus 2.0 numerical simulation method was used to verify and analysis with the research results.In addition,by control experiments with AMF,the effects of fissures on plant roots,leaves,endogenous hormones and also the mechanism of AMF to alleviate fissure induced root damage stress were studied.The main conclusions of this study are as follows:(1)Based on the dynamic monitoring of fissure development in the loess gully area of the northern wing and the aeolian sand area of the southern wing of Ningtiaota mine,it was found that ground fissures accelerated soil water loss,damaged plant roots,affected plant spatial distribution,and reduced plant height and crown growth rate,inhibited plant growth;The morphological characteristics of fissures were the important factors related to fissures' ecological effects.Under conditions of low soil infiltration rate in the loess gully area,fissures were found to have the effect of increasing precipitation infiltration;Fissures inhibit the shoot growth of surrounding plants.Half a month after the fissure interference,the shoot growth rate was significantly reduced.Two months after the fissure interference,the fissures' inhibitory effect on plant height and crown width was prominent and reached a significant level of difference;The root damaged plants had a certain bioremediation effect.Two months after the fissure interference,the roots of the root damaged plants tended to grow on the opposite side of the fissures.In the aeolian sandy area,root tips of Artemisia ordosica and Salix cheilophila increased significantly by 55.0and 14.1%,respectively.In the loess area,root tips of Artemisia ordosica increased significantly by 40.3%,and the plant height and crown growth rate gradually returned to the control level;Compared with the loess area,the degree of plant recovery was greater in the aeolian sandy area,and the remediation effect was more significant.(2)Fissure morphology is an important factor affecting soil water movement.Obtaining the morphological characteristics of fissures with high accuracy is an important prerequisite for revealing the mechanism of fissures and soil water.The traditional steel rule measuring method not only has low accuracy,but also can only obtain the fracture width,length,and depth performance information.It is difficult to build a threedimensional model of the fissures by steel rule measuring method,and it cannot obtain fissures' detailed morphological characteristics,such as volume,surface area and other three-dimensional information.In order to obtain comprehensive characteristics of fissure morphology and serve to the mechanism study of fissures affecting soil water,this paper applied and compared another three types of ground fissure detection methods to obtain three-dimensional models of fissures.Each method has its own advantages: The threedimensional laser scanning fissure monitoring method can obtain the three-dimensional morphology information of the shallow part of the fissure,and the deep information of the fissure is difficult to detect.three-dimensional laser scanning combined with perfusion gypsum slurry method can completely obtain three-dimensional morphology information such as fissure width,depth,length,volume and area.However,the detection operation is destructive;The ground penetrating radar scanning method can non-destructively obtain the three-dimensional morphological model of the fissures,which is suitable for the observation of small fissures in the field and the acquisition of the morphological models of the indoor fissure simulation experiments.However,the fissure boundary discrimination will be subjectively affected,and the accuracy is relatively low.And the field implementation needs to excavate the side,the operation is complicated to operate and has a large workload.(3)The development of fissures has a direct impact on soil moisture,and to reveal the specificity of its water movement law compared with normal soil,more mechanism study is necessary.By the combination of indoor physical simulation and numerical simulation,the spatial distribution changes of soil water around fissures of different scales(FS 10,20,30,and fissure step heights of 10,20,30 cm respectively)were simulated.For the first time,the effects of ground fissures on the movement of surrounding soil water were observed.The results showed that the numerical simulation method of Hydrus 2.0was in good agreement with the physical simulation results,which both could reflect the soil water movement law around the fissures;ground fissures affect the spatial distribution of surrounding soil water and accelerate the loss of soil water around.The larger the scale of the ground fissure,the larger its scope of influence;The closer to the fissure wall,the lower the soil water content.As soil depth increased,the effect of fissures gradually decreases.In deep soils,the effect of fissures gradually decreased.Numerical simulation results: The impact distances of FS 10,20,and 30 were: 25,40,and 50 cm,and the impact depths were: 20,45,and > 65 cm.Physical simulation results: The impact distances of FS 10,20,30 were: 20,35,45 cm,and the impact depths were: 20,30,45cm;The artificial neural network modeling method was used to predict the soil moisture content around the fissures,and the effect of the fissure morphological characteristics on the soil water was analyzed according to the importance of the modeled independent variables.(4)In order to study the effects of fissure induced root damage stress and plant remediation,this paper studied the role of microorganisms on root damage stress remediation by designing the root damage stress simulation device.The results showed that,ground fissures led to significantly higher levels of endogenous abscisic acid(ABA)but significantly reduced levels of indole-3-acetic acid(IAA),gibberellins(GA)and cytokinin(CTK).In addition,ground fissures led to significantly reduced root biomass,total root length,root tip number,total root volume,plant nutrient content,leaf chlorophyll content and leaf area.The shoot biomass of root damaged maize decreased significantly by 46%.By contrast,Inoculation of Arbuscular Mycorrhizal Fungi(AMF)increased IAA and CTK levels in maize roots,reduced ABA levels,improved the hormone balance of damaged plants,increased total root length,root tip number,total root volume,leaf area and leaf chlorophyll content,increased nutrient content and increased shoot biomass by 34%(Harvested one month after fissure interference).(5)AMF has the effect of remediation on fissure induced root damage stress,but its remediation process is unknown,and its regulation mechanism needed to be further studied.In the current study,a root growth in-situ monitoring system was added to the simulation device to observe the remediation process of AMF regulating roots,leaves and endogenous hormones.The results showed that the growth of roots and leaves was related to hormone levels.One week after root damage,IAA and CTK levels in roots and leaves were both significantly reduced,while ABA levels were significantly increased.The roots of the root damaged plants tended to grow on the opposite side of the fissures.After six weeks of root damage,the levels of IAA and ABA in the leaves were restored,but the plant biomass,root and leaf development were significantly lower than those in the control.AMF regulates the development of roots and leaves by changing the level of endogenous hormones,increasing fine root percentage,which is conducive to improving the ability of plants to absorb nutrients and water,thereby alleviating the negative effects of root damage stress and promoting remediation of root damaged plants.One week after root damage,AMF significantly increased root IAA and CTK levels,reduced ABA levels,increased the fine root percentage,promoted the development of plant roots and leaves.Six weeks after root damage,both shoot and root biomass in mycorrhizal plants were increased by more than 31% compared with the control.The effect of AMF on promoting remediation of root damaged plants was significant.