Characteristics Of Organic Carbon And Regulation Of Its Decomposition In Acidic Tobacco-growing Soil

Straw incorporation was the most important measures to improve soil fertility and soil acidification.However,straw which returned to the field cannot be decomposed in a short time.More undecomposed straw were accumulated in soil,causing humus composition and carbon structure of soil were changed.Tobacco-growing soil of Tengchong City had long-term straw returning to the field,but the soil pH was still decreasing with each passing year.To identify the organic carbon characteristics of tobacco-growing soil with straw returning,solving the problem of unreasonable carbon composition of straw returning soil by promoting the decay of straw by cellulose degrading bacteria.Soil was improved to increase the quality and yield of flue-cured tobacco.The results of the reseach can be devided into the following parts:?1?we explored the differences of acidic tobacco-growing soils with different straw returning amount?from Tengchong,Changning and Yong'an City.?,which were described in terms of basic physical,acidity indexes,chemical properties,and carbon structure characteristics.The soil acid content was low and salt base saturation was high which collected by Tengchong City.However,the pH of the soil has been decreasing year by year during the growth phase of tobacco.But no significant effect has been found on the improvement of soil acidification while the land was treated with straw incorporation and the organic matter was increasing every year.In the ratio of humic acid to extractable humic substances?PQ?,HA/FA value,E4 value and the rA value at 1630 cm^-1 in the infrared peak band and the relative area after integration,the soil was collected from Jietou Town were significant higher than Jifei and Xiyang Town.However,the E4/E6 value and the?logK value were lower than them.It was showed that the composition of humic substances was high and complex in the soil of Tengchong City.?2?We set different pH values in the same organic matter and soil nutrient content of soil from Tengchong City and analyzed soil organic carbon structure,humus composition,the difference between the content of activated carbon and inert carbon components.The results showed that the HA/FA value of soil with low organic matter content will gradually decreased with the increase of pH.The soil with high organic matter content was increased with the increase of acidity,the HA/FA value was increased gradually,and the humus components with high stability was also increased.Under the same organic matter content,the infrared A2920/A1630 gradually increased with the increase of soil pH.It indicated that the carbon component with high activity in the soil was gradually increased and the carbon component with high stability was gradually reduced.?3?Analysis of the changes of organic carbon in the process of adding different types of straw cultivation through acid tobacco-growing soil in three regions.The soil organic matter and the organic carbon content of each humus component were significantly increased and the condensation degree and oxidation degree of the soil carbon structure were also decreased by added various types of straw compared with CK.It was found that the soil humus composition and carbon structure of group became simplified were included rapeseed straw incorporation,decomposed corn straw and decomposed rice straw group of Xiyang Town,decomposed rice straw and decomposed corn straw group of Jifei Town,and same as CK,decomposition rice straw and decomposition corn straw group of Tengchong Town after96 d.Long-term used of decomposed rice straw,fresh rice straw,decomposed corn straw and fresh corn straw to improve soil of Jietou Town was better than other group.Taking into account the cost of returning to the field and the efficiency of nutrient release,it was also applied cellulolytic agent to straw.?4?A cellulolytic bacteria,YN-1^T,was isolated from rice field from Jietou Town.Based on 16S rRNA gene sequence similarity comparisons,strain YN-1^T clustered together with other species of the genus Bacillus and showed highest similarities with Bacillus onubensis0911MAR22V3^T?98.0%?,Bacillus humi LMG22167^T?97.5%?,Bacillus timonensis10403023^T?97.4%?,Bacillus sinesaloumensis P3516^T?97.1%?and Bacillus cheonanensis PFS-5^T?95.9%?.The polar lipids were diphosphatidylglycerol,phosphatidylglycerol,phosphatidylethanolamine,two unidentified phospholipid,three unidentified aminophospholipid and two other unidentified lipid.the major fatty acids are iso-C_15:0,anteiso-C_15:0 and C_16:0 which is the major menaquinone component of members of the genus Bacillus.In summary,the genotypic,chemotaxonomic and phenotypic data presented in this study demonstrate that strain YN-1^T isolated from rice field represents a novel species in the genus Bacillus,for which the name Bacillus aciditolerans sp.nov.is proposed.?5?To deeply mine the degradation mechanism of the strain Bacillus aciditolerans YN-1^T,functional genomics were analyzed.Total 4,023 genes were involved in the genomic annotation of strain YN-1^T to participate in 183 metabolic pathways.The main metabolic pathways were metabolic pathways,biosynthesis of secondary metabolites,ABC transport,microbial metabolism in different environments,amino acid biosynthesis,two-component systems,and carbon metabolism.Total 126 genes encoding the CAZymes gene in the genome of strain YN-1^T.The highest proportion was glycosyl hydrolase GHs?60?,followed by carbohydrate esterase CEs?31?.The number of glycosyltransferase GTs,polysaccharide lyase PLs,carbohydrate binding module enzyme CBMs and auxiliary module enzyme AAs annotated genes were 20,5,7 and 3,respectively.The presence of 10 genes in the genome annotation provided the basis for the ability of strain YN-1^T to degrade cellulose,named GH1?2?,GH3?5?and GH43?3?,respectively.?6?To explore the impact on soil microbial diversity and clarify the changes in soil ecological environment in order to accelerate the decomposition of straw,the results showed that the dominant bacteria in each sample were Proteobacteria,Acidobacter,Bacteroides and Bacillus after 33 d.The Chao1 index,ACE index and Shannon richness index of the microbial species in the sample showed no significant difference between treatments.Principal component analysis showed that there was no significant change in total bacterial abundance and diversity over time,especially in the treatment group supplemented with microbial agents and the treatment group with only straw added.Cluster analysis showed that samples collected at similar times were clustered into one type and no significant impact on the original microbial community structure.It was indicated that the effect of decomposed straw incorporation and decomposed straw incorporation+microbial agent were better.?7?To find a cost-effective measure to use straw,the field experiment was designed to verify the effect of the best improved straw incorporation and the application of microbial agents to the field.The results showed that the cellulose decomposition microorganisms were beneficial to the decomposition of rice straw and corn straw after adding the microbial agent.The incidence and disease index of tobacco in each group were lower than that in CK,and the disease index of tobacco in rice straw and corn straw returning combined with microbial agent was lower than that of single straw returning.Compared with CK,straw+microbial agent treatment could increase the content of potassium,total sugar and reducing sugar in tobacco leaves after roasting.The lower middle tobacco leaves reached a significant level and reduced the chlorine content of the tobacco leaves in each part.The nicotine content in the middle and upper tobacco leaves of the added microbial treatment group were lower than CK.Compared with CK,the yield of 80 kg/667 m² tobacco treated with corn straw returning was significantly higher than that of 40 kg/667 m².It was indicated that rice straw,corn straw returning with microbial agent could significantly increase the yield of upper and middle leaves,thereby increasing the output value of the tobacco.