亚热带柑橘园土壤N2O排放规律及其产生机制

Citrus is the second largest fruit species in China, distributed mainly in subtropical regions with a wide range planted area reached 2.3 million hectares. Our previous study found that citrus orchard soil had a high potential of N2O emissions and increased with planting age. However, the emission and production mechanism of N2O from subtropical citrus orchard soils are not well known. In this study, citrus orchard with different planting age (2-4, 9-12, 18-22 and 28-32 years) and adjacent not reclaimed sample plots will be collected. Static chamber method will be used to study the annual variation of N2O emissions. The 15NH4NO3 and NH415NO3 tracing technique will be conducted to qualitify the contribution of different nitrogen transformation processes to N2O emissions and the respective production ratio. Molecular biological methods (eg. PCR-DGGE, Real-time PCR) will be used to study the community structure and numbers of functional microbes of citrus orchard soils with different planting age. At the same time, the variation of soil physical and chemical properties will be analyzed. And then, the regularity, production pathways and affecting factors of N2O emissions from citrus orchard soils with different planting age will be evaluate and the production mechanism of N2O emissions will be revealed. These results will provide basic theory for N2O emissions estimation and control measures of N2O emissions in subtropical orchard soil.

柑橘是我国第二大果树品种，主要分布于亚热带地区，面积达230万公顷。我们前期研究结果发现，亚热带橘园土壤具有较高的N2O排放潜势，而且随着种植年限的延长具有增加的趋势。然而，目前有关不同种植年限橘园土壤N2O排放规律和产生机制尚不明确。本项目拟选取不同种植年限橘园（未开垦样地、2-4年、9-12年、18-22年、28-32年）作为研究对象，采用静态箱法测定N2O排放量周年变化动态；采用15NH4NO3和NH415NO3同位素成对标记方法，研究土壤中不同氮转化过程对N2O产生的贡献率及产物比；采用PCR-DGGE、Real-time PCR等分子生物学方法研究土壤功能微生物群落结构与数量特征变化规律。同时测定土壤理化性质，分析N2O排放量和产生途径随种植年限的变化规律及其主要影响因素，揭示不同种植年限橘园土壤N2O产生机制。研究结果可为亚热带橘园土壤N2O排放量的估算和调控措施提供理论依据。

本项目以亚热带柑橘园土壤为研究对象，在果园原位条件下研究了N2O排放规律，在室内培养条件下研究了柑橘园土壤N2O产生途径及其主要影响因素。结果表明，柑橘园土壤在不施肥、有机肥和常规施肥处理条件下N2O平均排放速率分别为0.004、0.005和0.029 kgN•hm-2•d-1，排放峰集中于夏、秋季。影响N2O排放的主要因素包括土壤含水量、地温、NH4+和NO3-含量等。林地开垦为柑橘园后虽然土壤有机碳和全氮含量随种植年限的延长而提高，但土壤无机氮供应能力并没有随之增强，而且土壤保氮机制受到破坏、N2O排放最显著提高。果园耕作对土壤保氮机制的破坏效应主要集中在开垦后的前10年，而后逐渐降低，但持续到30年仍然存在。林地土壤N2O排放主要来源于异养硝化和反硝化过程，而柑橘园土壤主要来源于自养硝化和反硝化过程。该项目研究结果可为柑橘园管理和N2O减排措施的制订提供理论参考。