Screening Of Microbe Producing Organic Acid And Its Application In Improving Saline-alkali Soil

Soil is not only an important nature resource,but also a basic resource that the rapid development of human society and economy depend on.Human beings are currently faced with serious environmental deterioration,such as soil erosion,environmental contamination,and global warming and so on,besides,people are also become more and more in short of nature resources and energy resources due to exhaustive exploitation in the past few decades,thus turning the unavailable soil into valuable resources to help dealing with such intractable problems is proved to be one of the most significant measures.On the other hand,there are large areas of saline-alkali soil all over the world which contains incalculable resources,however,they cannot be used efficiently due to its extremely poor life condition,as a result,the development of saline alkali land has become an urgent and arduous task.The saline-alkali soil is usually seriously salinized and alkalized,easy to knot,and has bad air permeability and poor soil fertility,which lead to the survival problem of most plants and microbes,and a very few living creatures that could survive here usually have natural ability to tolerate salinity and alkalinity,many practices have proved that it is a green and feasible measure to improve the saline-alkali soil with plants or microorganisms that have natural ability to tolerate salinity and alkalinity.Besides microbe is one of the important components among soil ecosystem and plays an important role in the restoration and maintenance of soil ecosystem,study the special metabolic function of microorganisms with natural resistance to salinity and alkalinity and put them into practice in improving saline-alkali soil,which are of great significance to improve the effect of improving saline-alkali soil through microbe.This paper focuses on the screening of microbe which not only has the ability to resist salt and alkali,but also can produce high yield of organic acid,then apply the strain in different ways into the saline-alkali soil in the arid area inland,thereby exploring whether it can reduce the soil pH rapidly through neutralizing alkaline compounds with the acid that it produced,in addition,the effect of strain dosage and application mode on saline-alkali soil pH could also be studied,which would provide us the basic reference on reasonable fertilization mode and strain dosage for the strain's further application to the improvement of saline-alkali soil in the future.Firstly,find appropriate methods to isolate the strain with high yield organic acids and natural ability to tolerate salinity and alkalinity from natural saline-alkali soil,choose Gause Nov.medium whose nutrition is not very rich as selective medium due to the fact that most saline-alkali soil is also poor.At the same time,Congo red,which is less toxic to microorganism and has sensitive color-change ability with pH,is choose as an acid indicator in screening medium.Finally,3 strains that meet the requirements were isolated from seriously salinized and alkalized soil,while the one with the strongest acid producing ability was chosen as the research object and was named SQ21,SQ21 was classified as Aspergillus Niger after the identification on its morphology and molecular biology.Secondly,try to find suitable materials from crop waste as a medium for carrying the strain,then make microbial inoculant by fermenting the strain in the material.Make the dry materials such as wheat bran,soybean dregs,corn flour,tangerine powder and bagasse into solid fermentation medium with 50%humidity,then inoculate equal amount of SQ21 into each kind of solid fermentation medium and culture under the same condition,dissolve all the spore of SQ21 that growing on each kind of solid fermentation medium,dilute the spore suspension and count the spore amount through hemocytometry under the microscope.Comprehensively evaluate the total spore amount,the Characteristics of each crop material and the convenience when handling each material,the bran was considered to be the best medium for carrying the strain.Thirdly,make large amount of microbial inoculant by fermenting the strain in bran,and inoculate 2.5 g,5 g,10 g,20 g microbial inoculant on 500 g natural saline-alkali soil,then apply equal amount microbial inoculant on another natural saline-alkali soil and make the soil humidity smaller than the former one,next,apply equal amount of microbial inoculant to 500 g sterile salinized soil.At last,test the soil pH under different treatments regularly to find the effect of the inoculant dosage,soil moisture and the quantity of SQ21among community on the saline-alkali soil pH.The result suggested that the soil pH reducing degree was positively related to the dosage of SQ21,and pH of soil with high humidity decreased less than the soil with lower humidity,on the other hand,SQ21 has a more community advantage of living in the sterilized saline-alkali soil over living in the natural one,which was due to the fact that the strain can make the sterile saline-alkali soil soil pH drop sharper than the natural saline-alkali soil.Further more,after applying3.18×10~100 cfu spores of SQ21 singly into 500 g saline-alkali soil,the soil pH decreased by2.24 in 50 days.Lastly,add base fertilizers such as bran,compound fertilizer or sodium nitrate into500 g saline-alkali soil and apply different amount of SQ21 spores into the soil regularly,then plant chrysanthemum seedlings on each saline-alkali soil with different treatments.After testing the soil pH and Chrysanthemum height,the results showed that combining SQ21 with bran or sodium nitrate could make the soil pH significantly decreased,the soil pH decreasing degree of each were 1.12 and 1.37,while comparing the growth of chrysanthemum growing on saline-alkali soil that was been improved by SQ21 and different base fertilizer,the height and crown diameter of chrysanthemum treated with SQ21 and bran increased the most,comprehensively evaluate the pH reducing degree and the growth of chrysanthemum,it could be concluded that the combination of SQ21 with bran is better than SQ21 with compound fertilizer or sodium nitrate in improving the saline-alkali soil.The research proved that the SQ21 played an important role in reducing the saline-alkali soil pH and promoting plant growth.