Diversity Bacterial Communities And Their Effect On Promotion Decomposition During Straw Returned

Up to now, China is still an agricultural country. Because there was a series of affected factors, such as high crop cropping index, short cropping arrangement time, high yield of straw, and straw was difficult to be decomposed, etc. which became the key factor of restricting the straw returned to field. Application of straw biodegradation inoculants could promote the straw decomposing, but microbial groups involved in cellulose degradation process are very diverse in the nature. Besides the cellulose degrading microorganisms, there are many other microorganisms, especially soil bacteria, involved in the straw degradation process in the nature.In this paper, wheat straw was used as experimental material, four field experiments were designed, i.e., straw returned+straw-decomposing inoculants at the dry land (T1); straw returned to the dry land directly (T2); straw returned+straw-decomposing inoculants in paddy field (T3); straw returned to the paddy field directly (T4). The wheat straw material was taken at the 10d,30 d and 60 d. and the decomposing characteristic was evaluated by the tension method and chemical composition analysis. And bacterial strains were isolated and purified, their genetic diversity was performed by BOXAIR-PCR,16S rDNA PCR-RFLP and 16S rDNA sequencing analysis; the diversity of bacterial communities in the process of straw decomposing was studied. Furthermore, the bacteria with high straw decomposing ability was screened and used to obtain the mixture of bacterial strains, and then the pot experiment was designed to investigate the promoting effect of mixed bacterial inoculants. The main results were as follows:(1) The decomposing effect of straw returned was very obviously, and was different between the different treatments. The tensile strength and chemical component analysis showed that, after the straw decomposition agent was used, the wheat straw tensile strength decreased from 65.7 N at the beginning (0d) to 2.02 N in the end (60d) in dry field; and the content of cellulose, hemicellulose, lignin decreased from 45.63%,24.53% and 25.37% to 25.58%.13.36%, and 19.77%, respectively; However, the wheat straw tensile strength decreased from 65.70 N at the beginning (Od) to 2.93N in the end (60d) in the paddy field; and the content of cellulose, hemicellulose, lignin decreased from 45.63%,24.53%,25.37% to 27.06%,13.81%, and 20.60%. The results also showed that the straw decomposed status of decomposition agent inoculated was better than that of CK both in the dry land and in the paddy field. When the treatment was the same, the straw decomposed status in the dry land was better than that in the paddy field.(2) Using dilution-plate method, a total of 110 bacterial strains were collected from all samples, their genetic diversity was determined by BOXAIR-PCR,16S rDNA PCR-RFLP, and 16S rDNA sequences of representative strains. The results revealed that the bacteria groups involved in straw decay process was very abundant, and the tested bacteria distributed in 15 genus, and more than 30 species, included genus Bacillus, Ochrobactrum, Pseudomonas and Enterobacter. Of them, strains belonged to Bacillus and Ochrobactrum existed in four treatments; strains belonged to Pseudomonas existed in three treatments except T1; strains belonged to Enterobacter existed in three treatments except T2. The bacterial population quantity of different treatments changed as the follow:T2>T1>T3>T4; and T2 had the highest amount of bacterial populations, while, T4 had the lowest.The bacterial genetic diversity was existed in the same treatment at the different stages of straw decomposed; of them, bacteria belong to genus Bacillus had the largest numbers, and the species was very abundant, which was the predominant one. Bacteria belonged to genus Enterobacter was founded in the sample taken at 10d; however, Bacteria in genus Klebsiella and Exiguobacterium was founded in the sample at 60d. Along with thedecay time extended, the quantity of bacterial communities reduced gradually.(3) Application of bacterial mixture effectively improved the straw decomposition rate. Based on the tensile strength, content of cellulose, hemicelluloses and lignin of wheat straw, treatment of decomposing inoculant+bacterial mixture had the best effect in the simulating dry land, and its tension strength decreased from 83.69 N to 21.58N, which was better than that in treatments of CK, decomposing inoculant used only, and bacterial mixture used only. The content of cellulose, hemicellulose, lignin decreased from 44.48%, 26.92%, and 26.89% to 13.96%,14.81%, and 19.98%; when doing it in simulating paddy field, the treatment of decomposing inoculant+bacterial mixture also showed the best effect, its tension strength decreased from 83.69 N to 33.16 N; and the quantity of wheat straw cellulose, hemicellulose, and lignin content of straw decreased from 26.92%, 44.48%,15.16% to 26.89%.26.92%, and 20.44%, respectively.