碳底物含量对厌氧条件下水稻土N2、N2O、NO、CO2和CH4排放的影响

理解底物碳氮对厌氧条件下水稻土排放氮素气体——氮气(N2)、氧化亚氮(N2O)和一氧化氮(NO)以及二氧化碳(CO2)和甲烷(CH4)的影响,有助于制定合理的温室气体减排措施,定量了解反硝化产物组成对碳底物水平的依赖性,也有助于氮转化过程模型研发中制定正确的关键过程参数选取方法或参数化方案.本研究采用粉砂壤质水稻土为研究对象,设置对照(CK)和加碳(C+)两个处理,前者的初始硝态氮和可溶性有机碳(DOC)含量分别为~50 mg·kg-1和~28 mg·kg-1,后者的分别为~50 mg·kg-1和~300 mg·kg-1.采用氦环境培养-气体及碳氮底物直接同步测定系统,研究了完全厌氧条件下碳底物水平对上述气体排放的影响.结果表明,CK处理无CH4排放,而C+处理可观测到CH4排放;C+处理的综合增温潜势显著高于CK处理(P<0.01);NO、N2O和N2排放量占这3种氮素气体排放总量的比重,在CK处理分别约为9%、35%和56%,在C+处理分别约为31%、50%和19%,处理间差异显著(P<0.01).由此表明,碳底物水平可显著改变所排放氮素气体的组成;对于旱地阶段硝态氮比较丰富的水稻土,避免在淹水前或淹水期间施用有机肥,有利于削减温室气体排放.

Effect of Carbon Substrate Concentration on N2, N2O, NO, CO2 and CH4 Emissions from a Paddy Soil in Anaerobic Condition

Understanding the effects of carbon and nitrogen substrates concentrations on the emissions of denitrification gases including nitrogen (N₂), nitrous oxide (N₂O) and nitric oxide (NO), carbon dioxide (CO₂) and methane (CH₄) from anaerobic paddy soils is believed to be helpful for development of greenhouse gas mitigation strategies. Moreover, understanding the quantitative dependence of denitrification products compositions on carbon substrate concentration could provide some key parameters or parameterization scheme for developing process-oriented model(s) of nitrogen transformation. Using a silt loam soil collected from a paddy field, we investigated the influence of carbon substrate concentration on the emissions of the denitrification gases, CO₂ and CH₄ from anaerobically incubated soils by setting two treatments: control (CK) with initial soil nitrate and dissolved organic carbon (DOC) concentrations of~50 mg ·kg^-1 and ~28 mg ·kg^-1, respectively; and DOC added (C⁺) with initial soil nitrate and DOC concentrations of~50 mg ·kg^-1 and ~300 mg ·kg^-1, respectively. The emissions of denitrification gases, CO₂ and CH₄, as well as concentrations of carbon and nitrogen substrates for each treatment were dynamically measured, using the gas-flow-soil-core technique and a paralleling substrate monitoring system. The results showed that CH₄ emission was not observed in CK treatment while observed in C⁺ treatment. Aggregate emission of greenhouse gases for C⁺treatment was significantly higher comparing with the CK treatment (P<0.01). The mass fractions of NO, N₂O and N₂ emissions in total nitrogen gases emissions were approximately 9%, 35% and 56% for CK treatment, respectively; and approximately 31%, 50% and 19% for C⁺treatment, respectively, with significant differences between these two treatments (P<0.01). The results indicated that carbon substrate concentrations can significantly change the composition of nitrogen gas emissions. The results also implicated that organic fertilizer should not be applied to nitrate-rich paddy soils prior to or during flooding so as to mitigate greenhouse gases emissions.