The Improvement Effects Of Bentonite And Microbial Agents On The Soil Of Mu Us Sandy Land

Mu Us Sandy Land is one of the most serious desertification areas in China.Due to the high permeability of the sandy desertification soil,nutrients and mineral elements in the surface layer of the soil are easily transported and accumulated to the deeper layers of the soil with water,resulting in to the phenomenon of slow growth and yellow needles in the large-scale planted Pinus sylvestris var.mongolica plantation in the study area,which seriously restricts the stability of the ecological function of the plantation vegetation.In view of the above problems,through in situ modulation and soil column leaching experiments,using high-throughput sequencing technology,to analyze the impact of bentonite alone and bentonite with microbial agent under two control modes,bentonite addition on soil physicochemical properties,soil profile water and fertilizer transport characteristics,bacterial community structure composition and potential ecological functions,to reveal the effect of bentonite and microbial agent on sandy soil improvement and the study revealed the effect and mechanism of bentonite and microbial agents on the improvement of sandy soil,in order to provide a theoretical basis and technical support for the cultivation of young camphor pine forests in Mu Us sandy land.The specific research results are as follows:1.The contents of surface soil moisture content（SWC）,cation exchange capacity（CEC）,organic carbon（SOC）,nitrate nitrogen（NO₃^--N）and ammonium nitrogen（NH₄⁺-N）all increased significantly with the increase of bentonite addition,but the improvement effect of bentonite combined with microbial agents was more obvious,and the CEC and SOC accumulated in different degrees in the later stage of the experiment.In addition,the contents of available phosphorus（AP）and available potassium（AK）in the surface soil increased significantly with the addition of bentonite in the early stage of the experiment,and increased in the single application mode of bentonite in the late stage of the experiment,but decreased in the mode of combined application of microbial agents in bentonite.2.Under the two control modes,different treatments have the greatest influence on SWC of 0-20 cm soil layer,and the treatment of adding 3%bentonite has a more significant effect on improving soil moisture content（p<0.05）.Under the two control modes,different treatments have the greatest influence on soil available nutrients in 0-20 cm soil layer.NO₃^--N,NH₄⁺-N,AP and AK gradually increase with the increase of bentonite content,and the content of available nutrients in each treatment gradually decreases with the deepening of soil profile.The results of soil column leaching experiments show that the single leaching loss of available nutrients gradually decreases with the increase of bentonite addition,and the contents of NO₃^--N and AP gradually decrease with leaching times,while the contents of NH₄⁺-N and AK first increase and then gradually decrease with leaching times.3.Adding bentonite in the two models significantly increased the richness and diversity of soil bacterial community in the early stage of the experiment（p<0.05）.With the increase of bentonite addition,the richness and diversity of bacteria gradually increased,and there was no significant difference among the treatments in the later stage.The results of PCo A analysis showed that there was a significant difference inβdiversity between the treatments and the control in the early stage of the experiment（p=0.001）,and the two treatments with the largest bentonite addition remained quite different in the later stage,while the differences in other treatments gradually decreased.The application of bentonite in the early stage of the experiment significantly increased the relative abundance of Proteobacteria and Blastomycetes,significantly decreased the relative abundance of Actinomycetes and Acidophiles（p<0.05）,and the abundance of Firmicutes showed an overall upward trend in the later stage.4.The function prediction based on FAPROTAX shows that,compared with CK,with the increase of bentonite content,the abundance of bacteria leading to aromatic compounds,aromatic hydrocarbons and lignin degradation in soil decreases;The abundance of microorganisms leading methanol oxidation,cellulose and xylan decomposition in soil increased with the increase of bentonite.In the process of nitrogen cycle,the abundance of bacteria leading urea decomposition function increased significantly with the increase of bentonite addition,while the abundance of bacteria leading nitrogen fixation decreased with the increase of bentonite.NO₃^--N,SWC and AK were the main factors affecting the horizontal dominant species of soil genus in the early stage of the experiment,and AP and AK had a greater influence on the horizontal dominant species of soil genus in the later stage of the experiment.In conclusion,the enhancement of water holding capacity,water content and nutrient content of the sandy soil by applying bentonite in this study was more significant and became more effective as the amount of bentonite added increased.Compared with bentonite application alone,bentonite combined with microbial agents significantly improved the CEC and SOC storage in soil,but not for NO₃^--N,NH₄⁺-N,AP and AK contents in the soil.In addition,the application of bentonite significantly affected the soil bacterial community diversity and species composition,while having some effects on the potential ecological functions mediated by soil microorganisms.