[Responses of soil organic carbon and microbial community structure to different tillage patterns and straw returning for multiple years.]

Soil organic carbon is essential for maintaining terrestrial ecosystem function and mitigating soil degradation. Soil microorganisms participate in soil carbon cycling. They are affected by tillage methods and straw returning. A split-plot design was adopted in this experiment. The whole-plot treatment had two tillage methods, subsoil tillage (ST) and rotary tillage (RT). The split-plot treatment included full straw returning (F) and no straw returning (0). The microbial community structure and carbon sequestration genes were assessed by Illumina sequencing technique. Soil organic carbon contents were measured during 2012-2017. The results showed that 1) subsoil tillage and straw returning significantly increased pH, microbial biomass carbon, total nitrogen, silt content, and clay content, while significantly decreased sand content; 2) during the test period (2012-2017), soil organic carbon (SOC) content under all treatments showed an increasing trend, but the increment for average SOC content under straw returning and subsoiling treatments was significantly higher than that of no straw returning and rotary tillage by 33.2 % and 30.6%, respectively; 3) Proteobacteria was the most abundant type of bacteria in the soil, followed by Acidobacteria and Gemmatadanetes; 4) STF treatment maintained high microbial diversity; 5) Excepted for soil sand content, soil pH, microbial biomass carbon, total nitrogen, silt content and clay content all caused the variation of soil microbial community structure under the STF treatment in the direction of SOC accumulation; 6) in addition to the gene abundance in the di- and oligosaccharides metabolic pathway, the gene abundance in the metabolic pathways for CO2 fixation, central carbohydrate metabolism, fermentation, one-carbon metabolism, organic acids, sugar alcohols and glycoside hydrolases showed that subsoil tillage was significantly higher than rotary tillage, with posi-tively correlation with soil organic carbon content. Therefore, the combination of subsoil tillage and straw returning could improve basic soil properties, affect soil microbial community structure, and increase the capacity of soil carbon fixation, thus providing a realistic basis for solving soil degradation.土壤有机碳对维持陆地生态系统功能和缓解土壤退化问题至关重要,土壤微生物参与土壤有机碳的循环过程,而耕作方式与秸秆还田影响土壤有机碳和微生物群落.本试验采用裂区试验设计,耕作方式为主区,分别设深松(ST)和旋耕(RT)处理,副区为秸秆还田量,分别设秸秆全还田(F)和秸秆不还田(0)处理,采用Illumina测序技术测定土壤微生物群落结构和固碳功能基因,并测定了2012—2017试验年间土壤有机碳含量.结果表明: 1)深松耕作和秸秆还田均显著提高了pH、微生物生物量碳、总氮、粉粒含量、黏粒含量,而显著降低了砂粒含量; 2)试验年间各处理的土壤有机碳(SOC)含量均呈增加趋势,但与旋耕耕作和秸秆不还田处理相比,深松耕作和秸秆还田处理的平均有机碳增量分别显著提高30.6%和33.2%; 3)土壤中最丰富的细菌类型为变形菌门,其次为酸杆菌门和芽单胞菌门; 4)深松秸秆还田处理(STF)具有较高的微生物多样性; 5)除砂粒含量外,土壤pH、微生物生物量碳、总氮、粉粒和黏粒含量均促使深松秸秆全还田处理下的微生物群落结构向着有利于有机碳积累的方向发生变异; 6)除二糖和寡糖代谢途径外,CO2固定、发酵、主要碳水化合物代谢、一碳代谢、糖醇、有机酸、糖苷水解酶类的代谢功能基因丰度均表现为深松耕作显著高于旋耕,且均与土壤有机碳呈正相关关系.因此,深松结合秸秆还田能够改善土壤基本性质与土壤微生物群落结构,有利于增加土壤固碳能力和解决土壤退化问题.