【作者】 丁维新；

【导师】 蔡祖聪；

【作者基本信息】 中国科学院研究生院（南京土壤研究所） ， 土壤学， 2003， 博士

【摘要】 为了阐明我国沼泽湿地甲烷排放的数量、甲烷排放的时空变化特点及其控制因素、植物在甲烷排放过程中的作用和排干沼泽农业利用对大气甲烷氧化的影响,在野外测定了沼泽湿地甲烷排放通量、沼泽水中甲烷浓度、水溶性有机碳(DOC)和乙酸含量,同时测定了沼泽氧化还原电位、温度、植物地上部分生物量和密度,室内培养试验研究了沼泽水产甲烷潜能。三江平原毛果苔草沼泽在植物生长期间甲烷排放通量变化在0.16~54.6 mg CH4 m-2 h-1之间,平均19.6 mg CH4 m-2 h-1。青藏高原若尔盖地区苔草泥炭沼泽甲烷排放通量波动在0.16~10.0 mg CH4 m-2 h-1之间,平均2.96 mg CH4 m-2 h-1。青藏高原高海拔导致的夏季温度较低是引起该地区沼泽甲烷排放量低的主要原因。初步估算我国沼泽湿地甲烷年排放总量为1.76Tg。毛果苔草对内源甲烷的氧化作用大于对甲烷的产生作用,乌拉苔草对两者的影响大致相当,而小叶章则对甲烷的产生作用大于对甲烷的氧化作用。在淡水腐泥沼泽(freshwater marsh)中,随着沼泽静水层深度的增加,植物种类由禾本科植物变为莎草科植物,植物传输甲烷的能力显著提高,占沼泽甲烷排放总量的比例从31%上升到72%~86%。三江平原沼泽湿地甲烷排放呈如下规律:毛果苔草沼泽>乌拉苔草沼泽>小叶章沼泽。静水层不同不仅引起其上生长的植物种类不同,而且也导致被水淹没的植物立枯量不同,使得沼泽中水溶性或易还原性有机碳含量产生差异,进而引起沼泽产生的甲烷数量不同,最终表现在甲烷排放通量的不同。在同种植物生长的沼泽不同采样点之间甲烷排放通量也存在一定的差异,这是由于植物地上部分生物量和植物密度的不同所致。毛果苔草沼泽甲烷排放存在明显的昼夜变化,午夜0:00出现最低值,大约在上午9:00达到最大值。小叶章沼泽排放的甲烷不仅数量少而且昼夜变化幅度小。引起沼泽湿地甲烷排放昼夜变化的主要原因是温度和植物光合作用产生的并传输到植物根茎和根际的氧气数量不同,使得植物根茎和根际中甲烷氧化和产生的数量在一天的不同时段不同,从而改变了沼泽水和根茎中的甲烷浓度,以及甲烷产生对温度昼夜变化的响应。毛果苔草沼泽水中甲烷浓度也存在明显的季节性变化规律。植物生长前期沼泽水中低的甲烷浓度不是由于乙酸供应限制了甲烷产生,而是由于低的温度和较高的氧化还原电位限制了甲烷的产生。沼泽不仅是大气甲烷的源,当沼泽排干后也是大气甲烷的汇。然后当排干沼泽被开垦为农田时,土壤氧化大气甲烷的能力受到强烈的影响。对土壤的耕翻破坏了甲烷氧化菌群落原有的最佳生境(optimal niche),提高表层土壤的容重,增加大气中氧气和甲烷扩散进入土壤的阻力,降低了土壤氧化大气甲烷的能力。氮肥的施用提高了土壤中NH4+的含量,可能激活土壤硝化菌的繁殖,降低甲烷氧化菌的数量和活性。排干沼泽土壤农业耕种初期氧化大气甲烷能力的降低主要起因于耕种行为本身,而氮肥施用则起着缓慢但长久的影响。更多还原

【Abstract】 To estimate the magnitude of methane emission from mires in China and to understand①temporal and seasonal pattern of methane emission from the freshwater marsh,②the effect of plants on methane emission from the freshwater marsh and③cultivation, fertilizer application and set-aside effects on atmospheric methane uptake in the drained marsh, the fluxes of methane emissions from and methane, dissolved organic carbon (DOC) and acetate concentrations in porewater in the freshwater marsh or the peatlands as well as redox potential in the vertical profile and plant biomass were measured in the field in Sanjiang plain, Heilongjiang province, northeast China, and in Hongyuan county, Sichuan province, west China.The flux rate of methane emission from the peatland in Qinghai-Tibet highland and the freshwater marsh in Sanjiang plain ranged from 0.16 to 10.0 mg CH4 m-2 h-1 with an average of 2.96 mg CH4 m-2 h-1 and 0.16-54.6 mg CH4 m-2 h-1 with an average of 19.6 mg CH4 m-2 h-1. The low flux in Qinghai-Tibet highland was due to low methane production stemmed from low temperature in summer. Based on our in situ measurement and the available data measured in previous studies around China, the estimated budget of methane emission from mires in China was 1.76 Tg a-1.The fraction of methane emission through Carex lasiocarpa, Carex meyeriana and Deyeuxia angustifolia was 72, 86 and 31%, respectively. Carex laisocarpa made a greater contribution to methane oxidation than to methane production and Carex meyeriana contributed equally to both functions, whereas Deyeuxia angustifolia stimulated methane production. As the depth of the standing water in the freshwater marsh increased and cyperaceous plants replaced the gramineous plants, the capacity of plants to transport methane from the marsh into the atmosphere increased, however the comprehensive effect of plants on methane production decreased.The flux rate of methane emission from the freshwater marsh vegetated with the different type of plants over the measuring period was in the following order: Carex lasiocarpa > Carex meyeriana > Deyeuxia angustifolia. Standing water depth determined the type of marsh plants, which governed methane transport, and the amount of plant litters inundated in water, which resulted in the difference in dissolved organic carbon for methanogenesis. The latter in turn affected methane concentration in porewater and methane emission. The aboveground plant biomass and plant density controlled spatial variation of methane emission from plots within a certain marsh.There was an apparent diel variation of methane emission from the marsh vegetated with Carex lasiocarpa with a peak at 9:00 and the lowest at 0:00. By contrast, an unclear diel pattern was observed in the Deyeuxia angusitfolia marsh. The diel variation was due likely to the variation of methane oxidation in the rhizome and rehizosphere, which was caused by the difference in the magnitude of oxygen produced through plant photosynthesis over the course of the day, and to the variation of methane production responding to diel variation of temperature.There was an apparent seasonal variation in methane concentration in porewater in the Carex lasioarpa marsh. Low metehane concentration in June was due likely to low temperature and high redox potential resulted from the more oxygen content in the rhizosphere rather than to unavailability of acetate, which inhibited methane production.The marsh is not only a source but also a sink for atmospheric methane when it was drained. Cultivation of the drained marsh enhanced bulk density of the surface soil and greatly destroyed optimal niche of methanotrophic community, which enhanced diffusion resistance of methane and oxygen and reduced methane uptake rate. Nitrogen fertilizer application increased NH4+ content in the surface soil, which possibly decreased methanotroph population and activity, leading to reduction of methane uptake. Cultivation strongly affected methane uptake rate at the initial stage of marsh cultivation and nitrogen fertilizer slowly reduced but persistently affected methane uptake.更多还原