Effects Of Cellulose-decomposing Bacteria On The Degradation Of Returned Straw And Its Mechanisms

Straw returning is an efficient approach to improve soil physio-chemical properties.However,the slow decomposition of straw under natural conditions can decline the crop yield and increase the pests and diseases.To overcome these drawbacks,this study examined the influence of straw-decomposing microbial inoculant on straw.To minimize the instability effects of the field conditions,we used the soil microcosm method combined with GFP（Green Fluorescent Protein）labeling,Q-PCR（Quantitative Polymerase Chain Reaction）detecting,16S r RNA sequencing,and solid-state nuclear magnetic resonance（SS NMR）techniques to systematically analyze the colonization quantity of cellulose-decomposing bacteria in the tested soil,the changes of indigenous microorganisms composition after inoculation with cellulose-decomposing bacteria,the decomposition rate of returned straw,as well as the chemical composition of the residues.The main research results were as follows:1.The overall survival status of Bacillus amyloliquefaciens SQR9（SQR9）in the tested soil was better than Cellulosimicrobium cellulans MC29（MC29）.The survival status of SQR9 showed a downward trend.On day 3,the survival quantity in Fluvo-aquic Soil,Yellow-cinnamon Soil and Shajiang Black Soil were 10.27,9.21,and 8.97 log₁₀copies/g,respectively.While the corresponding values were 6.95,6.51,and 6.90 log₁₀copies/g after120 days,respectively.MC29 showed an upward trend,with 6.27（in Fluvo-aquic Soil）,5.71（in Yellow-cinnamon Soil）,and 5.89（in Shajiang Black Soil）log₁₀copies/g on day 3,respectively,and 6.02（in Fluvo-aquic Soil）,6.39（in Yellow-cinnamon Soil）,and 6.12（in Shajiang Black Soil）log₁₀copies/g after 120 days,respectively.2.Inoculation with cellulose-decomposing bacteria reduced the diversity of soil bacterial community,and affected the composition of indigenous microorganisms.After 3 days of SQR9 inoculation and 120 days of MC29 inoculation,significant decreases of 2.09%and1.24%happened in the bacterial diversity of Fluvo-aquic Soil and Shajiang Black Soil.Compared with the aseptic control,the indigenous microorganisms composition of Fluvo-aquic Soil inoculated with SQR9 and MC29 changed significantly after both 3 and120 days.For Yellow-cinnamon Soil and Shajiang Black Soil,the indigenous microorganisms composition of only SQR9 inoculated soils were significantly different from the aseptic control on day 3 indicating the strong regulatory effect of SQR9 on soil indigenous microorganisms community composition.3.The effect of cellulose-decomposing bacteria on straw decomposition amount was generally promoted,while the effect on straw decomposition degree was not significant.At the early stage of inoculation,the straw decomposition amount of MC29 treatment with Fluvo-aquic Soil increased significantly and the decomposition amount change rate was26.2%.At the end of the experiment,except for SQR9 inoculated Fluvo-aquic Soil with a decomposition amount change rate of-13.6%,MC29 inoculated Yellow-cinnamon Soil and SQR9 inoculated Shajiang Black Soil significantly promoted straw degradation with the decomposition amount change rates of 13.8%and 5.92%,respectively.The linear fitting results showed significant positive correlation between the decomposition amount change rate of MC29 inoculated straw and the colonization quantity after 3 days on inoculation.Besides,significant positive correlation occurred among the decomposition amount change rate of MC29 inoculated straw with the colonization quantity and the change rate of indigenous microbial diversity after 120 days.Nevertheless,the decomposition amount change rate of SQR9 inoculated straw had no significant correlation with the colonization quantity and the change rate of indigenous microbial diversity after 3 and 120 days.The results of the solid-state NMR revealed that the A/O-A value of straw residues decreased after inoculation with cellulose-decomposing bacteria,particularly for MC29 inoculated Fluvo-aquic Soil after 3 days.Herein,the decomposition degree change rate of straw residues was-39.7%.Linear fitting results also indicated no correlation between the decomposition degree change rate of straw residues with the colonization quantity and the change rate of indigenous microbial diversity for both bacterial strains after 3 or 120 days of inoculation.In this study,inoculation of Shajiang Black Soil and Yellow-cinnamon Soil with SQR9and MC29,respectively,significantly improved the decomposition rate of straw after 120days.In conclusion,the capability of cellulose-decomposing bacteria for straw decomposition is mainly associated with its characteristics.The survival of cellulose-decomposing bacteria is determined by the soil biological and abiotic factors.Cellulose-decomposing bacteria not only can promote the straw degradation,but also it can regulate the composition of indigenous microbial community to produce a synergistic effect.However,to respond the research gaps,our future works should examine the capability of cellulose-decomposing bacteria for straw decomposition under the actual field condition for longer time.