The Process Of Straw Degradation And Mechanism Of Straw-degrading Microbial Succession In Upland Red Soil

China is an agricultural country,the annual yield of rice straw is very huge.The low content of organic matter is an important factor that restricts the quality of the red soil.Returning rice straw to the field is one of the important measures to improve the quality of red soil.The structure of rice straw is complex,the degradation and transformation processes in the soil are affected by factors such as soil organic matter content and related microbial communities.Microorganisms participate in the whole process of rice straw decomposition,and there is succession of microbial communities.However,the degradation of rice straw in red soil with different levels of fertility and related functional microbial communities are still unclear.This study selected upland red soil with different fertilities as research material,including unfertilized soil?CK?,balanced inorganic fertilized soil?NPK?,organic fertilized soil?OM?.This study used matagenomic analysis to identify the diversity of soil carbon degradation genes among different fertilization treatments,and to understand the degradation potential of rice straw in soil with different fertilities from the perspective of functional gene composition.Soil suspension system was constructed to detect the degradation of straw through the method of Scanning Electronic Microscopy?SEM?,and high-throughput sequencing was used to analyze the core functional microbial groups in the degradation process of the rice straw.¹³C-cellulose was added to build an indoor microcosmic incubation system,combined with DNA-stable isotope probing technology?DNA-SIP?and high-throughput sequencing technology,to study the active cellulose degrading microbial groups and microbial succession mechanism in soil at different fertility levels.The main results were as follows:?1?Matagenomic analysis found that the composition of carbohydrates active enzymes and the functional genes differed significantly between CK soil and OM soil.The relative abundance of carbohydrates esterase,glycoside hydrolase and glycosyl transferase in CK soil were significantly higher than that in OM soil.The relative abndance of polysaccharide and carbonhydrate-binding module in OM soil were significantly higher than that in CK soil.The relative abundance of cellulase and hemicellulase in CK soil were significantly higher than that in OM soil,while the relative abundance of lignin enzyme in OM soil was significantly higher than that in CK soil.The results showed that the degradation potential of straw in soil with different feitility was different.?2?The straw degradation experiments in soil at different fertility levels showed that the weight loss rate and degradation degree of straw in OM soil system were significantly higher than that in CK soil system.The degradation rates were 37.8% and 26.0%,respectively.During the process of straw degradation,the bacterial community composition attached to the surface of the straw in the CK and OM soil systems also changed significantly,and the richness of the microbial community involved in straw degradation in the OM system was higher than that in the CK system.In the early stage of CK soil culture system,the straw degrading microorganism groups are Flavobacterium,Pedobacter,Burkholderiaceae,Clostridiaceae_I and Ruminiclostridium_I.Acidobacteriales,Clostridiaceae_I,Ruminiclostridium_I,Methanobacterium is dominant in the late stage of straw degradation in CK soil.In the early stage of OM soil culture system,the straw degrading microorganism groups are Flavobacterium,Pedobacter,Burkholderiaceae,Cellvibrio,Pseudomonas,Stenotrophomonas and Ruminiclostridium_I.Acidobacteriales,Flavobacterium,Pedobacter,Hydrogenispora,Ruminiclostridium_I,Burkholderiaceae,Pseudomonas,Methanobacterium and Methanosarcina is dominant in the late stage of straw degradation in OM soil.?3?In the CK,NPKand OM soil systems,the proportion of ¹³CO₂ generated from cellulose degradation to the added ¹³C-cellulose was 10.2%,16.3%,and 26.8%,respectively.The cellulose labeling experiment found that the degradation rate of cellulose in CK,NPK and OM systems had a similar trend,all of which showed a rapid rise in the early stage of incubation,the degradation rate reached the highest value when the incubated for 5 weeks,and the degradation rate gradually decreased in the subsequent incubation.The dominant cellulose-degrading microorganisms were different in different treatments.The main cellulose degradation microorganisms in CK soil system were Acidobacteria,Bacteroidetes and Proteobacteria;The main cellulose degradation microorganisms in NPK soil system were Acidobacteria,Actinobacteria,Proteobacteria and Firmicutes;The main cellulose degradation microorganisms in OM soilsystem were Actinobacteria,Bacteroidetes,Proteobacteria and Gemmatimonadetes.In the early stage of CK soil system,the cellulose degrading microorganism groups are Niastella,Mucilaginibacter,Burkholderia-Caballeronia-Paraburkholderia and Massilia,Occallatibacter and Actinospicais dominant in the late stage of cellulose degradation in CK soil system.In the early stage of NPK soil system,the cellulose degrading microorganism groups are Nocardia and Streptomyces,Occallatibacter,Nocardia and Rhodanobacteris dominant in the late stage of cellulose degradation in NPK soil system.In the early stage of OM soil system,the cellulose degrading microorganism groups are Streptomyces,Massilia and Gemmatimonas,Streptomyce,Massilia and Caulobacter is dominant in the late stage of cellulose degradation in OM soil system.In summary,the predicted results based on functional genes were inconsistent with the actual degradation of rice straw and cellulose.Therefore,speculating the ability of rice straw degradation in soil with different levels of fertilities active carbohydrate enzymes was inaccurate.The common microorganisms of rice straw attachment microorganisms and cellulose degrading microorganisms are Acidobacteria,Bacteroidetes and Proteobacteria at the phylum level,and Mucilaginibacter and Cellvibrio at the genus level.The degradation microorganisms of rice straw were different in the soil with different organic matter levels,and the the degradation microorganisms successed with the incubation time.This study provides a more comprehensive understanding of the degradation process of straw in the soil,which can provide a theoretical basis for the improvement of soil fertility and the utilization of crop straw resources.