| In arid areas of Northwest China,the soil is poor and the ecological environment is fragile.The aeolian sand in the mining area covers many Quaternary palaeochannels,and is a valuable source of shallow ecological water.The diversity of clay minerals content,varieties and grain-size,in the soil of palaeochannels,not only affects soil water movement,but also profoundly affects soil microbial community structure and abundance change,and has far-reaching influence on soil physicochemical properties and soil evolution.In particular,it is rich in illite,K-feldspar and other clay minerals.It has great potential in enhancing sandy soil fertility and improving soil water holding capacity.The interaction of microbe and clay minerals occurs widely in nature,which not only plays an important role in the soil nutrients cycles and plant growth,but also as a sensitive indicator of environmental changes,which is of great significance in monitoring and evaluating the ecological environment of the mining area.Therefore,the study of soil clay-microbe interaction and its growth promoting effect can provide a theoretical basis for the rational use of microbial reclamation technology to improve the soil quality of shallow buried palaeochannels.It is also an objective demand to realize ecological restoration in the western mining area in China.This paper focuses on the essential problem of soil clay-microbe interaction mechanism,and chooses the mining subsidence area of the Shendong mining area as the research area.Through the characteristics of the distribution of the sediment composition and the microbial quantity in the field investigation of the mining subsidence area,the relationship between the sediment components and the microorganism in the river channel is established by the redundancy correlation analysis(RDA).In order to further clarify the mechanism of interaction between clay-microbe in river channel sediments,the best conditions and mineral modification characteristics of the interaction between clay minerals and potassium solubilizing bacteria(KSB)were studied by indoor static culture test.On this basis,a short-term pot culture was used to study the effect of KSB on the growth of maize in soils with different ratio of clay,and to screen the ratio of clay in soils by the best growth promoting effect.Then,3 types of river channel stratum models were built by soil column simulation.The effect of KSB and AM fungi on the growth of maize in the river channel stratum models and the effect of different models on the microbial activity were studied.Finally,it is clarified that the mechanism of interaction between clay-microbe in soil and its growth promoting effect,providing theoretical basis for the rational exploitation and utilization of soil in shallow buried river channels,and providing theoretical support for the application of microbial reclamation technology in the ecological restoration of mining area.The main research results are as follows:(1)In order to establish the relationship between the composition of sediments and the population of microorganisms in the river channel,the distribution of grain-size,microbial quantity and physicochemical properties of river channel sediments were analyzed.The results showed that the quantity of bacteria,actinomycetes and microbes increased with the content of clay in the depth of 0~50cm in river channel sediments.In addition to actinomycetes,the quantity of 3 kinds of microorganisms in the depth of 50~200cm increased with the content of coarse sand and water content.RDA analysis showed that the quantity of fungi and bacteria was mainly positively related to the electrical conductivity,the average grain-size and water content.The quantity of actinomycetes was related to the content of coarse sand,clay content and grain parameters(skewness,kurtosis and standard variance).In addition,the main soil types in the study area are aeolian sand,sandy soil,clay and sandy clay,in which the content of clay minerals respectively is 3~6%,12~18%,20~25% and 10~12%.The main minerals consist of illite,illite-montmorillonite mixed-layer,K-feldspar,kaolinite and chlorite.There are mainly three stratigraphic types of shallow buried palaeochannels: channel,terrace and floodplain.(2)For further study the interaction of clay-microorganism,through the indoor static culture test,the optimal water content,the KSB inoculation concentration,the content and the types of clay in the soil were screened during the interaction between KSB and illite or K-feldspar or the soil with different ratio of clay.The influences of KSB on mineral structure,chemical component and the ability of nutrient absorption and release also were studied.The results showed that,the first,by the interaction between KSB and clay minerals,the optimal KSB inoculation concentration and water content of K-feldspar was 15%*70%,and of illite was 20%*55%.When soil clay content was 30%,which was the best clay ratio,the optimal KSB inoculation concentration and water content were 15%*100%.When the soil water content was <100%,the soil with clay content of 30% had better potassium releasing effect at 10% and 20% of the KSB inoculation concentration.The second,after the interaction between KSB and clay minerals,two valence cations in the aluminium-oxygen octahedron of illite were released,resulting in a vibration shift of the Si-O bond,and a decrease in the number of interlayer charges.Especially,the content of the water molecules with charge in the illite interlayers significantly reduced,resulting in the release of interlayer potassium ions.After the interaction of KSB-clay minerals,the rate of Si/Al in K-feldspar decreased,and K-feldspar gradually evolves towards the direction of Al-riching and silicon-pooring.The third,when the initial concentration of KCl was >20mg/L,the KSB increased the apparent adsorption potassium capacity of illite and the adsorption affinity.Also the KSB increased the ability of the illite to store potassium,but had no significant effect on the potassium desorption.The KSB increased potassium desorption quantity and desorption rate of K-feldspar,but had no significant effect on K-feldspar potassium adsorption process.(3)A short-term pot experiment was conducted to study the the synergistic effects of KSB-clay on the growth and mineral nutrients of maize,on the soil available nutrient and enzyme activity,and on the soil comprehensive fertility which was evaluated by the principal component analysis(PCA).The results showed that KSB could effectively increase maize growth and nutrient uptake under environmental stress.KSB significantly increased maize biomass,so the maize growth was the best in the soil with clay content of 68%.Nitrogen,phosphorus and potassium accumulation in maize and soil nutrient utilization was the highest with the optimum clay content of 45%.KSB and clay synergize promoted soil potassium migration and improved soil comprehensive fertility.At the clay content of 45%,the treatment of maize with KSB was the best to promote the increment of available potassium,and the treatment of maize with KSB had the best fixation on potassium in soil with 68% clay content.The KSB could help the soil potassium migration and plant potassium accumulation to be linear and stable,which was beneficial to the long-term management of soil potassium fertilizer.The KSB significantly increased soil comprehensive fertility in the soil with 68% clay content.(4)For purpose of studying the growth promoting effect of microbial combined remediation technology in shallow buried palaeochannel area,this paper set up 3 types of clay-sand interbedded soil column models to simulate the shallow buried palaeochannel strata in Shendong mining area.The growth promoting effects of KSB and AM fungi on maize growth in the 3 types of channel stratigraphic models were studied.The results showed that,the first,KSB and AM fungi combined to improve the biomass,mineral nutrient absorption and photosynthesis of maize in the thick clay-samdwich sand column,so to promote the growth of maize.In the thin sand-overlying clay column photosynthesis of maize at jointing stage was promoted.In the thin clay-samdwich sand column photosynthesis of maize at maturity was promoted.The combination of KSB and AMF in thick clay-overlying sand column significantly promoted the water use efficiency of maize leaves.The second,in the thin clay-samdwich sand column,the catalase activity decreased in the clay layer and increased in the sand layer.In the thick clay-samdwich sand column,the KSB and AMF increased the acid phosphatase activity and the easy to extract glomalin protein(EEG)content in the clay layer,and the KSB increased the catalase activity in the thin sand-overlying clay column and the thick clay-samdwich sand column.The third,MBN was significantly correlated with available potassium,soil water content and total nitrogen in soil.The MBC was significantly positively correlated with electrical conductivity,organic matter,acid phosphatase activity,and total glomalin protein(TG)and EEG.The distribution characteristics of MBC in different soil layers: Sand-samdwich > upper/down clay layer > surface and bottom sand layer.The distribution of MBN: Down clay layer >sand-samdwich > bottom sand layer > upper clay layer> surface sand layer.The MBC in the thick clay-samdwich sand column was significantly higher than that in the others,while MBN showed the opposite law.Therefore,the combination of KSB and AM fungi had the best growth promoting effect in the thick clay-samdwich sand column,and clay layer and sand-samdwich layer are beneficial to microbial activities.(5)In a word,the distribution and metabolic activity of microorganisms are influenced by the grain-size of sediments and hydrodynamic conditions in the river channel.By using the characteristics of clay and water conditions of sediments in palaeochannel,KSB and AM fungi have significant growth promoting effects on palnts in river channel depositional environment.This provides a scientific basis for the application of KSB and AM fungi in the ecological restoration of shallow buried palaeochannel. |
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