蚯蚓对农田土壤温室气体排放的影响，机理及调控

Soil trace gas metabolism has been one of the important research subjects about interaction between the Earth's spheres. Pedosphere, biosphere and atmosphere come into being interrelatively and mutually dependently in the cycling and dynamic process of soil C, N biogeochemistry. Earthworms, the most important macro-fauna in agroecosystem play an important role in nutrient cycling. Earthworms are one of the most important members of soil fauna in terrestrial ecosystem. However, little information of the impact of soil fauna especially earthworms on the generation of trace gases in agro-ecosystem is available so far. To identify the effects of soil fauna on greenhouse gases (CO2,CH4 and N2O) emissions from agro-ecosystem, the outdoor field experiments assisted with laboratory incubations will conducted under the same climate condition and agricultural management. The CO2, CH4 and N2O fluxes will be measured in situ using the static chamber technique and analyzed with gas chromatogram, soil respiration will be measured by using the closed-chamber IRGA method to determine the seasonal and diumal (24h) dynamic pattern. We will use Biolog, PLFA and molecule biology measurements to determine soil microbial (especially function genes in denitrifiers) properties, such as microbial biomass and microbial diversity. The primary objectives will be to examine the effect of earthworm on greenhouse gases emissions with residues applied (incorporation or mulching), to explore their processes and relevant mechanisms in agro-ecosystem, and to study soil carbon sequestration and its potential by earthworm inoculation in cropland ecosystems. The microcosm experiments throughout a short-term incubation will be conducted to assess effects of straw application and active earthworm inoculation on greenhouse gases emission, and to make clear the denitrification pathway and chemical composition of soil organic carbon fractions. This project will be conducive to deeply understand the role of earthwom on soil carbon carbon sequestration, soil nitrification and denitrification, and will provide a firm foundation for strategy of greenhouse gas emission reductions measures in agro-ecosystem.

蚯蚓是农田生态系统的重要组成部分,对土壤的碳氮循环和微量气体代谢有重要作用,但相关研究仍较缺乏。通过采用静态箱-气相色谱法研究田间条件下蚯蚓在农田生态系统中主要温室气体的排放通量；采用密闭气室红外分析法测量蚯蚓农田季节间和昼夜间的土壤呼吸及CO2排放速率变化特征；采用Biolog微平板法及分子生物学方法明确接种蚯蚓后土壤反硝化过程中的重要功能菌（Nar,Nir,Nor,Nos）生物量及生物多样性变化，旨在揭示蚯蚓对CO2和N2O排放的影响、对农田生态系统固碳能力、N代谢及反硝化作用的影响。采用培养实验研究施加不同C/N比秸秆后蚯蚓对温室气体排放产生的短期效应，重点观察N素矿化和利用情况，土壤有机碳形态及变化，明确蚯蚓对N2O排放的影响、机理，为正确评价土壤动物的生态功能提供依据。本项目的实施将有助于深入了解蚯蚓在农田生态系统中的管理固碳能力及其在土壤硝化、反硝化作用中的角色及调控因素。

蚯蚓是陆地生态系统中最重要的大型土壤动物之一，与土壤碳、氮循环关系密切。本课题通过培养实验结合田间长期定位实验，明确了不同生态型蚯蚓对土壤温室气体特别是N2O排放的影响；分析了蚯蚓对N2O排放促进效应的机理，并从微观和中观的角度，探讨了利用硝化抑制剂减少蚯蚓土壤N2O排放的途径。⑴在接种三种不同生态型蚯蚓的微系统试验中蚯蚓活动显著提高了土壤N2O的排放速率、土壤矿质氮含量，土壤的表观硝化率和随着蚯蚓的接种而显著升高。微系统中，蚯蚓与土壤微量气体代谢关系密切；⑵ 培养试验发现富集线虫土壤和接种蚯蚓土壤显著增加了温室气体的排放量。不同密度线虫土壤CO2和N2O排放的差异显著，线虫及土壤动物间的相互作用会影响微量气体代谢过程；⑶ 通过旱作水稻-冬小麦轮作盆栽试验的研究结果表明，在栽培前期，接种蚯蚓确实能够促进农田生态系统CO2的排放，表现为脉冲式排放，但是在整个生育期内，与未接种处理相比，蚯蚓并没有增加CO2的排放。在混施秸秆时，蚯蚓的存在甚至一定程度上降低了土壤中CO2的排放。在相对长期的试验中，蚯蚓活动增加了土壤有机碳库，与初期的物理扰动增加CO2排放不同的是，蚯蚓最终减少了土壤中CO2的逸失；⑷蚯蚓的存在显著提高了土壤N2O的累积排放量，但秸秆的不同施用方式下接种蚯蚓对N2O排放有显著影响，从机理上表明蚯蚓在促进N2O排放过程中，“营养富集过程”（NEP）较“肠道生理过程”（GAP）更适合解释这种现象；⑸在微系统培养条件下，比较了两种硝化抑制剂DMPP和DCD对蚯蚓排放N2O的动态影响。在接种蚯蚓土壤中，DMPP的减排效果优于DCD。土壤的硝化率和净硝化速率均随着蚯蚓的接种而显著升高，而两种硝化抑制剂均显著抑制了土壤的硝化率，降低了土壤的净硝化速率，并进而减少了土壤N2O的排放。⑹在大田栽培条件下，比较了秸秆混施和表施两种还田模式下，喷施DMPP对蚯蚓排放N2O的动态影响。施用DMPP能有效的抑制蚯蚓土中铵态氮向硝态氮的转化。DMPP是一种理想的田间硝化抑制剂，有助于减少蚯蚓所产生的N2O排放。