Effects Of Deep Loosening And Deep Straw Returning On Soil Organic Carbon And Microbial Community Characteristics In Black Soil

Deep loosening and straw returning,as two main technical measures in farmland management,are important ways to increase soil thickness,enhance organic matter content and improve soil fertility.However,it is still unclear what the advantages of the combination of deep loosening and straw returning are to improve the effects of single tillage on soil carbon cycle and microbial community structure.Therefore,based on the long-term experimental station of Black Soil at Jilin Academy of Agricultural Sciences in Gongzhuling,the dynamic changes of soil organic carbon?SOC?,active organic carbon fractions?dissolved organic carbon and microbial biomass carbon?and soil microbial phospholipid fatty acid?PLFA?contents in the 0-20 cm and 20-35 cm soil layers were analyzed by an in situ incubation after deep loosening and deep straw returning.The mechanisms of deep loosening and straw returning on SOC and soil microbial community characteristics were discussed.The results showed that:?1?Deep straw returning significantly increased active organic carbon fractions contents in the different soil layers.In the 0-20 cm soil layer,the SOC content did not change significantly within 0-360 days in the deep loosening treatment,but the contents of active organic carbon fractions and microbial quotient?MQ?were significantly?P<0.05?increased on the 30^thday and the 150^thday.The contents of SOC,dissolved organic carbon?DOC?,microbial biomass carbon?MBC?and MQ were higher in the deep straw returning relative to the conventional tillage treatment,with average increases of 2.96%in SOC,17.36%in DOC,18.16%in MBC and 14.80%in MQ.In the 20-35 cm subsoil layer,compared with the conventional tillage,the contents of SOC,active organic carbon fractions and MQ in the deep loosening treatment increased significantly?P<0.05?on the 30^thday,but each index was significantly lower on the 60^thday.The contents of SOC,DOC,MBC and MQ in deep straw returning treatment were higher 10.69%,24.86%,21.93%and 10.14%than those in conventional tillage,respectively.?2?The PLFA content of soil microorganisms in the different soil layers within 0-150days were significantly increased by deep straw returning.In the 0-20 cm soil layer,the contents of soil total PLFA and each microbial flora PLFA?bacteria,fungi and actinomycetes?in the deep loosening and deep straw returning treatments increased significantly?P<0.05?compared with the conventional tillage treatment during 0-150 days,especially in the deep straw returning treatment.Compared with the conventional tillage,the community diversity index of deep loosening and deep straw returning treated soil were significantly?P<0.05?increased within 60-150 days.Principal component analysis showed that the difference in incubation period was the main reason for the difference in microbial community structure in the 0-20 cm soil layer.In the 20-35 cm soil layer,the contents of soil total PLFA?18.39%and103.71%?,bacteria PLFA?19.17%and 109.12%?,fungi PLFA?21.38%and 143.37%?and actinomycetes PLFA?14.01%and 66.39%?were higher in the deep loosening and deep straw returning relative to the conventional tillage treatments.Within 60-150 days of incubation period,the total PLFA of each treatment and the PLFA content of each microbial flora were ranked as deep straw returning>conventional tillage>deep loosening treatment.When culturation for 360 days,those orders were conventional tillage>deep straw returning>deep loosening treatment.The Shannon-Winner diversity index?H?and Pielou evenness index?J?were significantly?P<0.05?lower in the deep loosening relative to the conventional tillage and deep straw returning treatments on the 30^thday.Principal component analysis showed that the difference in tillage measures was the main reason for the microbial community structure change in the 20-35 cm soil layer.?3?Deep straw returning significantly changed the characteristics ratios of soil microorganisms.In the 0-20 cm soil layer,the ratio of fungi/bacteria PLFAs in the deep straw returning treatment was significantly?P<0.05?higher than that in the conventional tillage and deep loosening treatments.Within 0-60 days,the ratios of cyclopropyl/monoenoic precursors PLFAs and isomeric/anti-isomeric PLFAs in the deep straw returning treatment were lower than those in the conventional tillage treatment,and cyclopropyl/monoenoic precursors PLFAs ratio in the deep straw returning treatment was the smallest on the 360^thday.In the20-35 cm soil layer,greater fungi/bacteria PLFAs ratio was found in the deep straw returning treatment than the conventional tillage and deep loosening treatments within 0-60 days.The gram-positive bacteria/gram-negative bacteria PLFAs ratio in deep loosening and deep straw returning treatments was higher 16.84%and 13.34%than that in conventional tillage treatment during 150-360 d,respectively.Compared with the conventional tillage,the ratios of cyclopropyl/monoenoic precursors PLFAs and isomeric/anti-isomeric PLFAs decreased significantly?P<0.05?on the 30^thday.?4?Soil microbial community characteristics were closely related to SOC and active organic carbon fractions.The contents of soil total PLFA and each microbial flora PLFA?bacteria,fungi and actinomycetes?and fungal/bacteria PLFAs ratio was significantly?P<0.01?positively correlated with SOC,DOC and MBC contents.