秸秆覆盖免耕与有机无机肥配施下黑土微生物对外源碳氮添加的响应比较

Comparison on responses of black soil microorganisms to exogenous carbon and nitrogen addition under no-tillage with straw mulching and combined application of organic and inorganic fertilizers

摘要:

目的 秸秆覆盖免耕与有机无机肥配施均能有效提升土壤肥力，但二者对微生物碳氮周转的影响机制尚待明确。方法 以常规耕作(CK)土壤为对照，有机无机肥配施(CM)和秸秆覆盖免耕(CT)土壤为处理组，采用¹³C标记葡萄糖结合稳定同位素核酸探针(DNA-SIP)技术的室内微宇宙培养实验，探究了外源葡萄糖与尿素添加条件下黑土微生物活动中的呼吸、矿化、异化分解(以¹³C-CO₂衡量)、同化形成稳定有机碳(以¹³C-SOC衡量)、激发效应、N₂O排放、碳中和及活性微生物特征。结果 对照(+水)处理中，土壤微生物呼吸与矿化强度依次为CK<CM<CT，CO₂最大排放速率分别为0.413、0.589、0.615 μmol/(g·d)。外源有机碳氮添加引发正激发效应，且效应强度为碳氮同时添加(Glu+N)>单加碳(Glu)>单加氮(N)，但激发效应未随外源有机质总量增加而持续增强。异化分解作用随外源添加量增加而增强，¹³C-CO₂累积量表现为CK (97.0 nmol/g)> CM (90.4 nmol/g)>CT (81.9 nmol/g)。然而，微生物同化作用产生的稳定¹³C-SOC含量在CT土壤中为296.4 nmol/g，高于CM土壤中的263.5 nmol/g。3种土壤的碳利用效率均约为80%，同时约30%的N₂O排放被¹³C-SOC的形成所抵消。碳中和分析显示，CK与CT土壤的CO₂净排放量较CM土壤高出50%。此外，外源碳氮添加下微生物繁殖中活性氨氧化微生物主要为氨氧化细菌中的亚硝化螺菌属(Nitrosospira)。结论 相较于长期有机无机肥配施，秸秆覆盖免耕在提升土壤肥力方面展现出更高的呼吸、矿化与固碳能力，且其异化分解能力也相对较低，但导致了较高的CO₂净排放量。

Abstract:

Objective Both no-tillage with straw mulching and combined application of organic and inorganic fertilizers can effectively enhance soil fertility. However, the mechanisms by which they influence microbial carbon and nitrogen turnover remain unclear.Methods Soil samples included conventional tillage (CK) as the control, along with two management treatments: soils under combined application of organic and inorganic fertilizers (CM) and no-tillage with straw mulching (CT). By employing DNA-stable isotope probing (DNA-SIP) with ¹³C-glucose in a laboratory microcosm incubation experiment, we investigated the responses of microbial activities in black soil to exogenous glucose and urea addition. Key processes examined included respiration, mineralization, dissimilatory decomposition (measured by ¹³C-CO₂), assimilatory formation of stable organic carbon (measured by ¹³C-SOC), priming effects, N₂O emissions, carbon neutrality, and active microorganisms.Results In the control treatment with water addition, soil microbial respiration and mineralization intensity followed the order of CK<CM<CT, which showed the maximum CO₂ emission rates of 0.413, 0.589, and 0.615 μmol/(g?d), respectively. Exogenous carbon and nitrogen addition induced positive priming effect, with the intensity ranking as simultaneous carbon and nitrogen addition (Glu+N)>carbon-only addition (Glu)>nitrogen-only addition (N). However, the priming effect did not continuously enhance with the increase in the total amount of exogenous organic matter. Dissimilatory decomposition enhanced as the amount of exogenous addition increased, with cumulative ¹³C-CO₂ emissions following the trend of CK (97.0 nmol/g)>CM (90.4 nmol/g)>CT (81.9 nmol/g). The content of stable ¹³C-SOC produced by microbial assimilation in CT was 296.4 nmol/g, higher than that in CM (263.5 nmol/g). The carbon use efficiency of soil in the three groups was approximately 80%, and about 30% of N₂O emissions were offset by the formation of ¹³C-SOC. Carbon neutrality analysis revealed that the net CO₂ emissions from CK and CT soil samples were 50% higher than those from the CM soil sample. Additionally, under the addition of exogenous carbon and nitrogen, the active ammonia-oxidizing microorganisms during microbial proliferation were primarily ammonia-oxidizing bacteria, specifically Nitrosospira.Conclusion CT demonstrates higher respiration, mineralization, and carbon sequestration capabilities and lower dissimilatory decomposition capability in enhancing soil fertility than CM, while it results in higher net CO₂ emissions.