Screening Of A Complex Microbial System Rss-4 For Effective Decomposition Of Rice Straws

In expecting to promote the circulating rate in the system of rice-cole rotation in Southern China which has low temperature and decomposition rate, a complex microbial system (CMS) RSS-4 with high ability of rice straw degradation was screened and constructed from the soils sampled from fields cultivated with straw-returning techniques for a long term in Sichuan Province by using the restricted cultivation and gradient-temperature induction methods in this study. The fermentation and cultivation characteristic, strain composition, the dynamic functional stability of the inoculants of RSS-4were studied. The lab-scale straw-returning effect experiment was also tested. The results suggested new thoughts for screening and application of new straw-decomposing inoculants, and accordingly accelerate decomposition, straw-returning application of rice straws in the tillage of rice-cole rotation. The main results of this research were as follows:Based on the easements on the microorganisms in different soils sampled from a long term straw-returning fields in Chengdu, Sichuan Procvince, and the weight-losing efficiency of rice straws, CMC/FPA/ xylan activities, the complex microbial system (CMS) RSS-4 with high ability of rice straw degradation was screened and constructed using the restricted cultivation and gradient-temperature induction methods. When RSS-4-induced rice straws degrading experiment was performed at 22℃, the pH value of the system increased at the initial stage and then slightly decreased until to 7.20. The CMC activity and xylan activity also showed an increase at the beginning and followed by an obvious decrease, with the peak values being 0.91 U and 3.40 U, respectively. At the end of fermentation (16 d), the weight of rice straws and the component cellulose and hemicellulose reduced to 45.0%, 55.5%and 44.1%, respectively. It was also found that the RSS-4 by the unsterilized method has better degradation effect than that of the RSS-4' by the sterilized method. The complex microbial system (CMS) was also demonstrated to have better decomposing efficiencyand functional stability and biosafety. It was also found that the RSS-4 has better degradation effect than that of the RSS-4'.Using pure culture dependent method and 16S rDNA clone library method, the strain composition of the RSS-4 were investigated.The results indicated that 25 OUTs were found by 16S rDNA clone library method and the dominant communities of complex microbial system (CMS) RSS-4 were Uncultured bacterium, Uncultured compost bacterium, Rhodanobacter sp., Klebsiella pneumoniae, Pseudomonas sp., Uncultured soil bacterium, Aeromonas sp. and Uncultured gamma proteobacterium. In contrast, only 4 bacteria and 4 fungi were found by cultivated using flat lineation.The dynamic changes of inoculants in the process of straws decomposition were studied by DGGE analyzing method. The results indicated that 12 bacterias and 18 fungi were found by DGGE method. The proportion of strains was different at various stages during the cultivating process. The microbes composition of RSS-4 were various and complex. Some were preponderant strains. Some worked at the initial stage and then disappeared quickly. Some were not appeared until latter stage. And some appeared alternatly. The result showed that the primary microbes were different at the different stage during the total process. And they promote the process of straw decomposition together. The stability exprements showed that in a continuous subculture, the pH value of the system have a similar change law in each generation. The changes in CMC activity, FPA activity and xylan activity were consistent. Moreover, the degradation rate in each generation was also consistent which suggested that the Complex Microbial System RSS-4 were stable in the aspects of enzyme activity production and straws decomposition. Its microbial strain composition was studied by DGGE. It showed that the microbial strain composition in generations from 15 to 23 of the continuous subculture in composite system was not changed, indicating a special stability of the strain composition.In the straw-returning to field experiments, the weight-losing efficiency of rice straws of Inoculant RSS-4 treatment was 9.6 percent higher than the control. More DGGE bands (i.e., microorganism alternation) were found in the RSS-4 treated one.