Screening And Utilization Of Microbial Strains To Promote Granite Weathering

With developing the economy,human beings make excessive use of natural resources,which has a great destructive effect on the ecological environment,resulting in landslides,exposed bedrock of abandoned mines,a sharp decrease in biodiversity,and restricting economic,environmental,ecological and social benefits.Therefore,the ecological restroration of the bare rock in slope moutain is urgent.Gut-soil seeding is the main technology for ecological restoration,but there are still many problems in its application.Plants growing on rocks are prone to break away from the rock surface or die after absorbing all the nutrients.In order to solve this problem,we carried out research on ecological restoration of rock slope vegetation to promote the integration of rock surface and vegetation.Granite is one of the most widely distributed rocks in Chinese mainland,and Amorpha fruticosa is one of the common tree species to green the slope.In this paper,granite and A.fruticosa were selected as the research objects,and studied the screening of microbial strains that promoting granite weathering and their effects on the growth of A.fruticosa.In order to separate and screen highly efficient microbial strains of weathing granite,soil samples and granite rock samples were collected from abandoned mine of Jinding mountain in Suzhou of Jiangsu province.The plate counting test showed that both in the shady or sunny slopes,the number of microorganisms at the bottom of the slope was the largest,while the number at the top of the slope was the smallest.The number of microorganisms in the sunny slope was significantly higher than that in the negative slope.The silicate medium and PD medium were used for liquid fermentation,and the contents of silicon were determined by inductively coupled plasma emission spectrometer?ICP-AES?.It showd that,19 bacterial strains and 25 fungal strains with weathering granite effect were screened preliminarily.Furtherly,one bacterium and one fungi with high granite weathering effects were separately isolated in nitrogen liquid fermentation culture medium and Czapek-Dox medium.Using microscopic morphological observation and physiological and biochemical tests,combining with Biolog microbial identification system and molecular biotechnology,the bacterial strain XB-1 is identified as Bacillus mucilaginosus,and the fungal strain XF-1 is identified as Aspergillus niger.Comparing their silicon release effects,it was found that A.niger XF-1 had better effect of granite weathing.Therefore,A.niger XF-1 was used as the target strain to study the weathering of granite and the growth promoting effect on A.fruticosa.This study we will conduct the research of rock weathering mechanism and growth promotion on Amorpha fruticosa of A.niger XF-1 which has optimal effect of granite weathering effect.The types of metabolites produced by A.niger XF-1during fermentation and leaching effects of silicon,iron,aluminum and sodium in granite were studied by shaking culture experiment and electron microscopy.In the medium containing granite powder,the contents of 6 organic acids?oxalic acid,tartaric acid,succinic acid,malic acid,acetic acid and citric acid?synthesized in the fermentation were increased gradually in the early stage,and decreased gradually in the late stage with the extension of fermentation time.Different kinds of amino acids were synthesized in different fermentation stages,and the medium containing granite powder was favorable for A.niger XF-1 to synthesize abundant polysaccharides.During rock weathering,it found that the element leaching effects of the mixture of organic acid,amino acid and polysaccharide is obviously better thanthat of the single metabolite.The three metabolites of A.niger XF-1 have synergistic effects,and A.niger XF-1 had the best effect of weathering granite.As a result,A.niger XF-1 and its metabolites organic acid,amino acid,polysaccharide and their mixture all have the effects of weathering granite,and the effect of A.niger XF-1 is better than that of single or mixed metabolites.The concentration of Si elements in the medium at different temperatures,pH values,transfer times and inoculations were determined by ICP-AES,and results were analyzed by grey correlation degree method.It show that A.niger XF-1 can promote granite to release more Si elements.PH is the main factor affecting the weathering granite of A.niger XF-1,followed by the inoculation quantity and temperature,and the inoculation times have the least influence.Moreover,the optimum temperature of A.niger XF-1 weathering granite is 28?,the optimum pH is 3,the optimum passage number is 5,he optimum inoculums size is 10⁷(spore number,mL^-1)The effects of different dilutions of A.niger XF-1 fermentation on soil nutrients and growth of A.fruticosa were studied by indoor pot experiment.The results showed that the 10^-22 diluted A.niger XF-1 fermentation significantly increased the total chlorophyll content in the leaves and the biomass content of A.fruticosa.The contents of available phosphorus,iron,copper,zinc,exchangeable calcium and magnesium in the fermentation of A.niger XF-1 were higher than that of the control soil.Therefore,A.niger XF-1 is a desirable strain of weathering granite,and has growth promoting effect on A.fruticosa.This study will provides high-quality microbial resources for ecological restoration of bare rock slope and theoretical basis for the sustainable development of ecological environment,and has important guiding significance for gut-soil seeding technology.