| In recent years, the deposition effect of microbial on rock mineral has received increasing concerns all over the world, and hence a hot field about earth science research is formed gradually. Our study focused on the effect of microbial on the structure of soil clay mineral and the mechanism of element release, providing the basis for transformation of soil mineral microbial and circle of elements, so as to improve the quality of soil environment in rhizosphere.The tested soil samples were collected from Chang sha,Hunan province, Wu han, Hubei provence, He ze, Shandong province and Xin xiang, Henan province, from which two effective silicate mineral-solubilizing bacteria HN1(Microbaterium sp.) and HN2(Paenibacillus mucilaginosus) were selected by their colony morphology, physiological and biochemical characteristics and16Sr DNA sequence. After three kinds of phyllosillicates (kaolinite, montmorillonite, illite) were cultivated by HN1or HN2for3-30days and by low molecular weight organic acids (oxalic and citric) for3-15days and by EPS (extracellular polysaccharides) secreted from HN2for3-15days, the Si release amount and the structure changes of the minerals were studied.The results indicated that:1) The pH of the cultivation medium of kaolinite, montmorillonite and illite cultivated by HN1and HN2tended to increase, ranging from4.13-4.53or6.03-6.80.2) Compared with CK, the soluble Si release amount from three kinds of minerals cultivated by HN1increased by4.81%-15.90%,32.25%-85.30%,5.48%-72.65%, while the soluble Si release amount from the minerals cultivated by HN2increased by48.69%-137.49%,35.57%-98.30%,62.13%-94.77%, respectively.3) As time went on, the increasing strength of the characteristic peak in the x-ray diffraction (XRD) picture of montmorillonite cultivated by silicate mineral-solubilizing bacteria tended to be weaker, while kaolinite and illite showed little change. Compared with HN1, HN2performed better to make more Si release and to destroy minerals more dramatically.4) After three kinds of minerals were cultivated by EPS secreted by HN2, the absorption peak of infrared spectrum of polysaccharide showed bathochromic effect at3399cm-1and1247cm-1, while blue-shift appeared at1649cm-1; montmorillonite could release more Si than kaolinite and illite cultivated by the same time and polysaccharide concentration. With the increasing of the polysaccharide concentration in cultivation solution, Si release from kaolinite, montmorillonite, illite cultivated for15days reached the maximum amount, and the characteristic peak in the x-ray diffraction (XRD) picture of montmorillonite got weaker and weaker whereas little change appeared for kaolinite and illite.5) With the increasing of cultivation time, the Si release amount of kaolinite and illite cultivated by organic acids at all tested concentrations reached the most amount at15days; For the same minerals cultivated by organic acids with the same concentrations, oxalic acid could make more Si release than citric acid, ranging from0.48-244.30μg/ml (SiO2); With the increasing of organic acid concentration, the Si release from minerals increased first and then decrease, and montmorillonite released more Si with the same conditions, and the characteristic peak in the x-ray diffraction (XRD) picture of montmorillonite got weaker and weaker, besides, oxalic performed better than citric, whereas little change appeared for kaolinite and illite. |
