【作者】 罗天相；

【导师】 胡锋；

【作者基本信息】 南京农业大学 ， 生态学， 2008， 博士

【摘要】 土壤微量气体代谢是地球各圈层相互作用的重要研究内容。土壤圈、生物圈以及大气圈之间通过碳(C)、氮(N)等元素循环及动力学过程相互作用,形成有机连续体。土壤生物是地球化学过程(生物小循环)的驱动者,调控微量气体代谢(例如温室气体的生成、消耗及传输等),进一步在大尺度上影响大气环境及全球气候变化。蚯蚓是分布非常广泛的土壤动物,在温带土壤无脊椎动物中其生物量最大,也是陆地生态系统中最重要的大型土壤动物之一。但是,关于土壤动物特别是蚯蚓对农田生态系统中温室气体排放影响的研究尚不多见。本论文主要通过田间的盆栽试验,辅以微系统的培养试验研究了在相同环境条件下,接种蚯蚓对农田CO2和N2O排放的影响,以及作物秸秆不同的施入方式下(混施和表施)蚯蚓和秸秆对稻麦轮作生态系统中CO2和N2O排放的综合影响、相关过程和可能机理。此外,通过原位富化获得不同密度食微线虫并接种蚯蚓的培养试验,研究了线虫和蚯蚓在微系统中对微量气体代谢的贡献及其相互作用,旨在进一步阐明土壤食微线虫和蚯蚓的相互作用及其对温室气体排放的影响。试验结果表明：(1)在施用秸秆并接种蚯蚓(赤子爱胜蚓,Eisenia foetida)的微系统试验中,21天的培养期内,蚯蚓活动显著提高了土壤C02和N20的排放量。与原土处理相比,单接种蚯蚓处理与单施加秸秆的处理导致C02排放量分别增加了60%和1.35倍,N20排放量增加了1.06倍和3.94倍。与单施加秸秆的处理相比,接种蚯蚓并施加秸秆的处理导致CO2和N2O排放分别增加了41%和45%。由于蚯蚓的直接排放量在该微系统中占有较大比例,当蚯蚓的直接排放量被扣除后,我们计算发现在未施加秸秆时,蚯蚓的存在并未导致CO2和N2O排放量的显著增加；而施加秸秆后,接种蚯蚓使CO2和N2O的累积排放量增加了21%和25%,均达到显著水平(p<0.05)。微系统中,蚯蚓取食秸秆并促使更多的秸秆分解转化,为CO2和N2O的产生提供了更多可利用的C、N源。施用秸秆显著提高了土壤微生物生物量,而单接种蚯蚓处理的土壤微生物生物量相比对照反而降低,土壤呼吸作用的加强不能单纯的归因于土壤微生物量的增加。接种蚯蚓使N03--N含量增加更显著,不同处理土壤矿质氮的分异主要取决于N03--N含量的变化,与NH4+-N相比,NO3--N含量对土壤N20排放的影响似乎更为显著。(2)不同土壤线虫密度下接种蚯蚓(赤子爱胜蚓,Eisenia foetida)的15天培养试验结果表明,土壤动物对土壤温室气体(C02和N20)排放有显著促进作用。与灭线处理相比,高密度线虫处理与高密度线虫加蚯蚓处理的CO2排放量分别增加了4.4倍和5.3倍,N2O排放量增加了1.8倍和2.7倍。接种蚯蚓在高密度线虫土壤中较接种在低密度线虫土壤中的C02和N2O排放量分别增加了13%和28%,均达到显著水平(p<0.05)。不同密度线虫土壤中CO2和N2O排放的差异显著,C02和N20排放量的变化显示出线虫在温室气体代谢过程中具有显著作用。两种气体的排放速率与土壤DOC浓度相关,微系统土壤中更高的DOC含量预示着土壤微量气体的代谢活动加强。扣除蚯蚓直接的排放量后,蚯蚓并没有产生更高的CO2排放量,但是当与未接种蚯蚓的对应处理相比,蚯蚓接种在高密度线虫土壤中时仍然显著提高了N20的排放量,土壤动物之间的相互作用及其对微生物种类特性的影响也是决定温室气体排放的重要原因。(3)通过田间试验,研究了秸秆不同施用方式以及接种蚯蚓(威廉腔环蚓,Metaphire guillelmi)对稻麦轮作土壤中CO2排放通量的影响。稻季和冬小麦栽培季节中,CO2累积排放量最大的均为混施秸秆处理,分别为1.60 kg·m-2和2.11kg·m-2,其平均排放速率为596.2 mg·m-2·h-1和540.6 mg·m-2·h-1。未加入秸秆和蚯蚓的对照处理累积排放量和排放通量均最低,平均排放速率为417.2 mg·m-2.h-1(稻季)和352.8 mg·m-2·h-1(麦季)。相比对照处理,秸秆处理(混施或表施)在整个生育期内显著提高了农田生态系统CO2的排放通量,不同秸秆施用方式CO2的排放有差异。稻季混施秸秆较表施秸秆增加了20%的CO2排放量,显著高于麦季的11%,表施秸秆有助于减少农田土壤C02排放量。蚯蚓的作用相对复杂：在稻季和麦季栽培的早期(前1个月内),蚯蚓显著促进了C02的排放。而在整个生育期内,表施秸秆加蚯蚓处理较表施秸秆处理未有明显差异；在混施秸秆的情况下,蚯蚓的存在甚至降低了麦季农田生态系统CO2的排放通量(p<0.05)。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C-CO2的逸失。通过相关性分析,我们发现SOC、全氮和CO2排放量呈极显著正相关,但MBC和DOC没有表现出与CO2排放量的显著相关性。试验结果表明,DOC与MBC不适合作为土壤有机碳长期累积性变化的指标,考虑到微系统中温室气体的排放速率与土壤DOC浓度相关,或许DOC适合指示短期瞬时的变化。(4)通过田间试验,进一步研究了秸秆不同施用方式以及接种蚯蚓(威廉腔环蚓,Metaphire guillelmi)对稻麦轮作系统N2O排放通量的影响。结果显示不论采用何种秸秆还田方式(混施或表施),施加秸秆和接种蚯蚓均能增加N2O的排放量。在秸秆表施情况下,接种蚯蚓处理在整个稻麦轮作生长季N2O的累积排放量达到最高的29.20 kg·hm-2,平均排放速率为439.2μg·m-2·h-1；对应的不接种蚯蚓处理为24.13 kg·hm-2,平均排放速率为362.9μg·m-2·h-1,两者差异极显著(p<0.01)。在秸秆混施时,接种蚯蚓后的处理N2O累积排放量为29.11 kg·hm-2,而不接种蚯蚓的对应处理N2O累积排放量为26.90 kg·hm-2,两者在稻季和麦季栽培后期均没有表现出显著性差异,表明农田生态系统中蚯蚓对N2O排放的贡献主要体现在促进秸秆混入土壤,从而加快N的分解和N20的排放。养分富集过程(NEP)较肠道关联过程(GAP)更好的解释了接种蚯蚓后土壤所表现出的生态效应。稻、麦两季观测结果表明,接种蚯蚓处理土壤N的矿化作用加强,矿质N含量提高,铵态氮含量比较稳定,硝态氮含量显著提高,其中表施秸秆接种蚯蚓处理硝态氮含量比未接种处理提高了20.1%(p<0.01),混施秸秆接种蚯蚓使硝态氮含量较未接种处理提高了11.7%。相关分析表明,硝态氮含量与N2O排放密切相关,接种蚯蚓后N2O排放潜力的提高可能与蚯蚓活动促进土壤氮素矿化特别是硝态氮含量的增加有关。微系统和田间的试验结果表明,在短时间内,蚯蚓和线虫对土壤CO2和N2O排放具有促进作用；在田间条件下,蚯蚓对土壤CO2排放的影响与秸秆施用方式有关。田间试验和微系统培养试验中所观察到的秸秆表施情况下N2O排放量的增加,从机理上表明蚯蚓的“营养富集过程”(NEP)较“肠道生理过程”(GAP)更适合解释蚯蚓对N2O排放的促进作用。更多还原

【Abstract】 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. Soil biota drive the biogeochemical process by regulating trace gas metabolism, and further influence atmospheric environments and the global climate change on larger scale. 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, N2O) emissions from agro-ecosystem, an outdoor pot experiment assisted with laboratory incubations were conducted under the same climate condition and agricultural management. The primary objective was to examine the effect of earthworm on greenhouse gases emissions with residues applied (incorporation or mulching), and to explore their processes and relevant mechanisms in agro-ecosystem. Also, laboratory incubations were carried out by inoculating different populations of nematodes and earthworm into soil samples to assess the influence of different populations of nematodes and earthworms on CO2 and N2O emission, and to make clear whether there exist synergies or antagonisms among soil faunal groups.(1) Short-term effects of actively earthworm (Eisenia foetida) with or without corn-straw residues on CO2 and N2O emissions were studied in a microcosm experiment throughout a 21 day incubation. Both residues application and earthworm presence resulted in significant differences in CO2 and N2O emissions relative to the control treatment. Cumulative emissions of CO2 and N2O in soil only with earthworm and soil only with residues were increased 60% and 1.35 fold for CO2,1.06 fold and 3.94 fold for N2O, respectively versus the soil treatment. The emission fluxes of CO2 and N2O in soil with residues and earthworm were 41% for CO2 and 45% for N2O higher than soil only with residues. Due to direct gases emissions of actively earthworms themselves are significant compared to fluxes measured from the whole systems, when emissions from earthworms themselves were deducted, cumulative amounts of CO2 and N2O emissions from the earthworm treatments are similar to that from the soil treatments. On the other hand, cumulative emissions of CO2 and N2O in treatment of earthworm and residues were 21% for CO2 and 25% for N2O higher than the treatment of residues (p<0.05). To supply easily available C, N as energy source for CO2 and N2O emissions, our experiment showed a much more positive earthworm effect on CO2 and N2O emissions in treatments with residues application. The value of MBC increased significantly by straw residues application meanwhile it decreased by earthworm inoculation, therefore the increase of CO2 emission cannot only attribute to MBC. The contents of NO3--N and NH4+-N increased significantly by earthworm inoculation, but not significantly by residues application, indicating that the relationship of N2O emission and NO3--N was more intimate than NH4+-N.(2) To determine the effects of soil fauna on greenhouse gases emissions, soil inoculated with different populations nematodes and earthworms (Eisenia foetida) were incubated for 15 days. Soil treated with greater populations of nematodes and earthworms enhanced CO2 and N2O emissions. Cumulative emissions of CO2 and N2O in the greater populations nematodes treatment and the greater populations nematodes with earthworm treatment increased by 4.4 times and 5.3 times for CO2, 1.8 times and 2.7 times for N2O, respectively versus the nematode-killed treatment. The effects of nematode abundance on CO2 and N2O emissions were apparent, nematodes play a important role in greenhouse gases metabolism. The greater populations of nematodes increased DOC value when compared with the lower populations of nematodes. Cumulative emissions of CO2 and N2O from the soils treated with different populations nematodes were positively correlated with DOC concentration measured at the start of gas sampling (p<0.05). Due to direct gases emission of earthworm activity were significant compared to amounts measured from whole systems, earthworm seem to be overestimated in greenhouse gases emissions. Earthworm does not contribute to higher CO2 release from soil instead of lead to increased production of the greenhouse gas nitrous oxide in Soil treated with greater populations of nematodes when gases derived from earthworm was deducted, which indicating that interaction between soil fauna and microorganism is also one of the determinant of greenhouse gases emissions.(3) An field experiment was performed to investigate the effects of residues and earthworm (Metaphire guillelmi) activities on CO2 emissions in a upland rice-wheat rotation system. The highest level of cumulative emissions and average rate of CO2 in upland rice season and wheat season were 1.60 kg·m-2 (596.2 mg·m-2·h-1) and 2.11 kg·m-2 (540.6 mg·m-2·h-1) respectively in the residues incorporated treatment, and the lowest level of cumulative emissions were both in the control treatment, the seasonal average rate of CO2 emissions from the control treatment were 417.2 mg·m-2·h-1 in upland rice season and 352.8 mg·m-2·h-1 in wheat season. Obviously, soil with straw residues application, relative to the control treatment, causing significant enhancement of CO2 emission. Two kinds of application of straw residues (incorporation or mulching) had different effect on CO2 emission, mulching decreased CO2 emission flux than incorporation. The presence of earthworm had complicated influence on CO2 emission. During the first 4 weeks both in upland-rice and wheat season, earthworms significantly (p<0.05) increased CO2 emissions. In contrast, significantly lower (p<0.05) CO2 emission amounts were measured at the rest of the entire annual cycle. The data suggested that earthworm activity was high during the first month due to the creation of burrows and incorporation of residues into the mineral soil. Both earthworm and straw residues application increased the SOC when compared with the control. Cumulative emissions of CO2 were positively correlated with the SOC and TN concentration measured at the end of the entire annual cycle. On the other hand, CO2 emissions were not positively correlated with MBC and DOC. (4) An field experiment was performed to further investigate the effects of residues and earthworm (Metaphire guillelmi) activities on N2O emissions. Both residues application (incorporation or mulching) and earthworm presence resulted in significant differences in N2O emissions. In the case of straw residues mulching, the cumulative emission amounts and average emission flux of N2O in the whole season significantly increased from 24.13 (362.9μg·m-2·h-1) to 29.20 kg-hm"2 (439.2μg·m-2·h-1) (p<0.01) in the presence of earthworm. However, if residues were incorporated into the soil, the earthworm effect disappeared except in the first stage of wheat season and emissions amounts were 29.11 kg·hm-2. Earthworm plays a more important role in N2O emission when residues mulched through mixing residue into the soil, switching residue decomposition to one with significant denitrification and N2O production. Soil mineral nitrogen (especially NO3--N content) was increased, and nitrogen mineralization was strengthened by earthworm activities. Earthworm inoculation significantly increased the contents of soil NO3--N by 20.1%(p<0.01) when straw residues mulched and up to 21.21 mg·kg-1, which means 11.7% increments when residues incorporated. Cumulative emissions of N2O were positively correlated with the NO3--N content measured at the end of the entire annual cycle.Both nematodes and earthworm presence resulted in significant differences in CO2 and N2O emissions accorrding to our outdoor pot experiment assisted with laboratory incubations. Short-term effects of actively earthworm (Eisenia foetida) and nematode abundance on CO2 and N2O emissions were apparent, nematodes play a important role in greenhouse gases metabolism. The presence of earthworm had complicated influence on CO2 emission which concerns the way of application of straw residues (incorporation or mulching). Earthworm plays a more important role in N2O emission when residues mulched both in field and microcosmic scales. It was concluded that the nutrient-enrichment processes (NEP) rather than the gut-associated processes (GAP) are responsible for the increased emissions of N2O in the presence of earthworms.更多还原