The Physiology Biochemistry And Remediation Effect Of AM Fungi On Damage Roots In Simulated Mining Subsidence

Coal,as an important mineral resource,provides energy security for China rapidly economic development.However,large-scale underground mining caused seriously land subsidence,and a series of ecological disaster such as plant roots damage,surface structure destruction and soil nutrient loss occured.,There are extremely scarcely precipitation,porous and poor loess and sparse vegetation in Ningtiaota mine areas.The reasons of sparse vegetation include: Firstly,roots exposed in the air not to absorb enough water and nutrients resulted from roots damage,which affected plant growth and development,caused by coal mining subsidence.Secondly,the available phosphorus content of loess was relatively low,so it was difficult to support enough available phosphorus for plant.Therefore,it is necessary to solve these two serious ecological environment problems to realize ecological restoration.Arbuscular mycorrhizal(AM)fungi form mutualistic symbiotic with most plants,promote plant to uptake nutrient,enhance plant resistance,and improve soil structure and properties.They have potential to realize ecological restoration and land reclamation.This paper aimed at the serious problem of roots damage caused by repeated mining subsidences of Ningtiaota mining area.Taking Caragana Korshinskii Kom.as host plant,which is the dominant species in coal mining area.Effect of AM fungi on the growth and resistance of Caragana and soil micro-environment was studied to explore AM fungi potential of ecological restoration on the plants with damage roots in mining area.In order to further explore repairing mechanism of AM fungi on the plants,laboratory simulation experiments were conducted.Then,from vertical and horizontal mining simulation of plant root damage,repairing effect of AM fungi on growth and physiological of maize was studied by the split root system composed of root,mycorrhizal and hyphal compartments.Morover,the impact factors and mechanism of ecological restoration effect of AM fungi were identified qualitatively with the stepwise regression and path analysis method,and the remediation ability of AM fungi on plant with different damage roots was evaluated quantitatively with entropy method.At last,combined with high content of insoluble phosphorus in soil of mining area,the simulated synergistic remediation effect of microbes and exogenous phosphorus on the maize with damage roots was investigated in this paper.Stepwise regression and path analysis were also used to explore the main impact factors and mechanism of ecological restoration of microbes and exogenous phosphorus.It provided the theoretical basis for the vegetation restoration and land reclamation,and the technical support for promoting the sustainable development of economy and environment in the mining area.The main conclusions are as follows:(1)AM fungi had the potential to repair plant with damage roots.The height,crown width and diameter of Caragana in inoculated area increased significantly compared with uninoculated area in August.AM fungi promoted Caragana roots growth and development,the root length,average diameter,surface area and volume of Caragana in inoculated area significantly increased by 151%,34.2%,116% and 129.3% respectively compared with uninoculated area.The soluble sugar concentration and catalase activity of Caragana leaves in inoculated area increased significantly,and it indicated AM fungi enhanced the resistance of Caragana to roots damage stress.The bacteria,fungi and actinomycetes numbers of rhizosphere in inoculated area were significantly higher than those in uninoculated area.The soil acid phosphatase activity(APA),organic matter(OM),alkali-hydrolyzable nitrogen(AN),available phosphorus(AP)and available potassium(AK)concentrations with inoculation increased significantly compared with control,and AM fungi improved the soil micro-environment where plant with damage roots.(2)The negative effect of vertical roots damage on growth and physiology of maize was relieved by AM fungi.When roots were damaged most,mycorrhizal colonization and hyphal density of mycorrhizal compartment remained 71.1% and 4.82m/g respectively.When 1/3 roots were damaged,the root gibberellins(GA),auxin(IAA)and cytokinin(CTK)concentrations of maize inoculated in mycorrhizal compartment significantly increased by 26.1%,20.3% and 86.8% respectively compared with the control,but the abscisic acid(ABA)concentration significantly decreased by 18.2%.AM fungi improved nutrient uptake of maize shoot and root,increased maize aboveground and belowground biomass,and restored its growth to that without roots damage and inoculation.AM fungi significantly improved soil micro-environment of maize with 1/3 roots damaged.AM fungi enhanced soil APA,increased glomalin and OM concentrations in the mycorrhizal and hyphal compartments,reduced soil pH value,and activated insoluble compound.The soil AN,AP and AK concentrations inoculated significantly increased,AM fungi promoted soil mineral elements to be transported to the plant.2/3 roots damage might be the critical point of AM fungi effect on the phytoremediation and soil improvement,However,AM fungi improved plant growth with 2/3 roots damaged and soil properties to some degree.(3)The negative effect of horizontal roots damage on growth and physiology of maize was relieved by AM fungi.Mycorrhizal colonization and hyphal density in mycorrhizal compartment with 1/2 roots damaged were 62.2% and 4.01m/g,respectively,and AM fungi still made a beneficial mutual symbiotic with maize.When 1/3 roots were damaged,compared with control,the root GA,IAA and CTK concentrations of maize inoculated in mycorrhizal compartment significantly increased by 47.6%,12.3%,and 72.9% respectively,but the abscisic acid concentration significantly decreased by 30%.AM fungi increased shoot N,P,K,Ca and Mg and root K,Ca and Mg concentrations of maize significantly,and restored maize growth to that without roots damage and inoculation.Moreover,AM fungi improved soil properties with roots damage treatment,enhanced soil APA in root and mycorrhizal compartments,increased soil glomalin,OM and available nutrient concentrations in mycorrhizal compartment,and promoted soil nutrient in root and hyphal compartments flow to plant.1/2 roots damage might be the critical value of AM fungi ecological restoration effect on the maize.(4)With stepwise regression and path analysis method,it was found that the main factors affecting effect of AM fungi on maize with vertically damaged roots were plant nutrients concentrations,root hormone levels and soil properties.The main factors affecting maize aboveground biomass were nutrients(P,K,Ca and Mg)concentrations of shoot and soil APA,while maize belowground biomass were mainly affected by root abscisic acid and nitrogen concentrations,shoot Mg and N concentrations and soil easily extractable glomalin(EEG)concentration;The effect of AM fungi on the plant with horizontal damage roots was mainly regulated by the root hormone levels and mycorrhizal effect.The main factors affecting the maize aboveground biomass were root ABA and Mg concentrations,shoot N concentration,hyphal density,soil total glomalin(TG)and EEG concentrations,while maize underground biomass was affected by the root GA,IAA,P and Mg concentrations,mycorrhizal colonization and hyphal density.Through entropy method,it was found that effect of AM fungi on the shoot growth of maize with vertical damage roots was significantly higher than that with horizontal damage roots.While effect of AM fungi on plant root growth with vertical damage roots was equal to that with horizontal damage roots.(5)The synergistic effect of microbes and exogenous phosphorus(EP)promoted plant growth with damage roots.When the roots were damaged unilaterally,single AM fungi inoculation(F.m),single phosphate solubilizing bacteria inoculation(CA)and combined inoculation(F.m+CA)significantly enhanced nutrient uptake of maize.Effect of single inoculation on root GA,IAA and CTK concentrations of maize was more significant,while that of combined inoculations on root ABA concentration was more significant.The highest aboveground and belowground biomass of maize was observed with inoculation of F.m+CA,moreover,the effect was more obvious with the increase of exogenous phosphorus concentration;When the roots were damaged bilaterally,and EP was 50 mg/kg,the root IAA and CTK concentration of maize inoculated with CA was highest,and the highest root GA concentration was observed with single inoculation of F.m.The maize aboveground biomass was highest with F.m inoculation,and restored to that with unilateral roots damage.When EP was 150 mg/kg,the root ABA concentration with single CA inoculation was lowest.The shoot and root N,P,K,Ca and Mg concentrations of maize inoculated with F.m+CA were highest,and N and P concentrations were restored to that with unilateral roots damage and without inoculation,the underground biomass was restored to that without roots damage.(6)The synergistic effect of microbes and EP improved soil pH,electrical conductivity(EC),APA,TG,EEG,OM,AK,AP and AN,and provided a better soil environment for plant growth with damage roots.When roots were damaged unilaterally,soil APA inoculated increased significantly.When EP was 50 mg/kg,soil pH was lowest but OM concentration was highest with F.m inoculation.Soil TG and EEG concentration inoculated with F.m+CA was significantly higher than that without roots damage and inoculation,and soil AK concentration with F.m+CA inoculation was highestt.When EP was 150 mg/kg,soil AN concentration with CA inoculation was highest;When maize roots were damaged bilaterally and EP was 50 mg/kg,soil pH inoculated was significantly lower than that without inoculation.The highest TG and EEG concentration of soil was observed with F.m+CA inoculation.The soil AP concentration with F.m inoculation was largest.When EP was 150 mg/kg,soil AN concentration with CA inoculation was highest.The highest soil EC and APA,OM and AK concentrations were observed with F.m+CA inoculation.The synergistic effect of microbes and EP on maize with damage roots was mainly regulated by the plant hormones and nutrient concentrations.Firstly,the dominant factors affecting maize shoot biomass were root GA and IAA concentrations,shoot N and K concentrations of maize,and soil EC.Secondly,the main factors affected maize belowground biomass were root ABA concentration,mycorrhizal colonization,shoot K concentration,soil APA,AP,AN and EEG concentrations.