The Microbial Mechanism Of Nitrogen Affects Straw Degradation And Soil Organic Carbon Mineralization

Returning straw and applying nitrogen are common measures for soil management of dryland in Karst region,study on the microbial mechanism of different nitrogen application level to regulate and control straw degradation and soil organic carbon transformation by dryland of long-term fertilization in Karst areas,it is important to improve the fertility and productivity of degraded land.The study focused on the typical brown lime soil,under the condition of indoor simulated culture,the organic carbon mineralization and transformation experiment of 100d were carried out,culture test seted 12 treatments,including 3 long-term fertilization treatments:no fertilization?CK??apply fertilizer only?NPK??straw returned to field with chemical fertilizer?NPKS?,Setted by four nitrogen levels:control?blank control,no any material?;S(add ¹³C-corn straw,the added amount was 2g/kg dry soil);S+N1(¹³C-corn straw with low nitrogen,the added amount was 0.07g/kg dry soil);S+N2(¹³C-corn straw with high nitrogen,the added amount was 0.20g/kg dry soil).Combining gas chromatography,chloroform fumigation and molecular biology techniques?real-time fluorescence quantitative PCR and high-throughput sequencing?,quantitative study of soil organic carbon conversion,microbial evolution and mechanism.The main results of this study were as follows:?1?During 100d cultivation,two dryland soils of long-term fertilization?NPK and NPKS?,the amount of carbon dioxide from straw was significantly higher than that soil of long-term non-fertilization?CK?,It was 1.25¹.7 times of CK.Although the degradation of straw at high nitrogen level in CK was higher than that of other materials,but it was still significantly below all processing of NPK and NPKS.So,the straw degradation in Karst was dependent on soil fertility and the level of exogenous nitrogen.?2?Straw and low level nitrogen application?S+N1?can effectively reduce the excitation effect intensity of soil organic carbon mineralization,but when nitrogen level was high?S+N2?,the stimulation effect of soil organic carbon mineralization increased,especially evident in CK and NPKS.So,when the straw is returned to the field,nitrogen fertilizer should be applied at the same time,otherwise it will lead to the mineralization of soil organic carbon,which is not conducive to soil carbon retention.?3?The tests of the soil microflora of 1d,5d and 100d were cultured showed that:35 phylums of bacteria,among which the phylums Actinobacteria,Firmicutes,Acidobacteria,Proteobacteria,and Crenarchaeota were the dominant phylums,sporosarcina spores was the dominant genera;The 40 phylums of fungus,among which the phylums Ascomycota,Basidiomycota,Chytridiomycota,Glomeromycota,Zygomycota were the dominant phylums,diaporthe husk genus was the dominant genera;High nitrogen level?S+N2?caused the abundance and diversity of bacteria and fungi decline,this indicated that exogenous nitrogen affected soil microbial community.?4?Analysis of variance analysis results showed that,long-term fertilization level and nitrogen addition significantly affected the soil soluble organic carbon,nitrate nitrogen,microbial biomass carbon,microorganism abundance and diversity.The results of redundant analysis showed that,soil environmental factors changed due to the addition of exogenous materials:soluble organic carbon?P=0.002,F=10.5?and nitrate nitrogen?P=0.004,F=29.1?were the significant factors affecting soil microbial community and straw degradation,thus affected organic carbon mineralization.In summary,long-term fertilization and exogenous nitrogen levels affected straw degradation and soil organic carbon mineralization in Karst dryland soil,and are accompanied by changes in microbial flora that drive straw degradation and soil organic carbon mineralization.The changes of the microflora were accompanied by soil organic carbon mineralization and straw degradation.The results provided theoretical basises and practical guidance for the rational management of straw return and nitrogen application in the Karst area.