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模拟氮输入对黄河三角洲盐沼湿地碳循环关键过程的影响
李隽永
Subtype博士
Thesis Advisor韩广轩
2021-05-15
Training institution中国科学院烟台海岸带研究所
Degree Grantor中国科学院烟台海岸带研究所
Place of Conferral中国科学院烟台海岸带研究所
Degree Name工学博士
Degree Discipline环境科学
Keyword氮输入 净生态系统 CO2 交换 光合碳分配 有机碳流失 盐沼湿地 Nitrogen input Net ecosystem CO2 exchange Photosynthetic carbon allocation Soil organic carbon loss Salt marsh
Abstract盐沼湿地具有较高的初级生产力和较低的土壤有机碳(SOC)分解速率,同时因其沉积效率极高,因而在捕获和埋藏有机碳方面具有极大潜力,被认为是地球上重要的“蓝色碳汇”。然而,在化肥大量生产和施用、化石燃料燃烧及畜牧业集约化经营等因素的共同作用下,越来越多的氮素(特别是硝态氮)通过地表径流和河流输入等途径进入近海生态系统,导致近岸水体富营养化现象日益加剧。径流和潮汐作用下大量氮素输入到盐沼湿地生态系统中,对碳循环过程产生深刻影响。本研究以黄河三角洲盐沼湿地生态系统为研究对象,设置氮输入野外控制试验、室内模拟氮输入和潮汐淹水耦合试验,并结合稳定碳同位素(13C)脉冲标记示踪技术,重点探讨不同氮输入水平梯度对盐沼湿地净生态系统CO2交换(NEE)、光合碳分配、土壤CO2和CH4排放、可溶性有机碳(DOC)流失等碳循环关键过程的影响机制,同时揭示氮输入水平和潮汐淹水频率对SOC流失过程的控制作用。主要结果如下: (1)氮输入增加显著增强了盐沼湿地生态系统CO2吸收能力,使其提高84.06%-220.54%,这主要得益于生长季生态系统CO2吸收能力随氮输入升高而显著增强。氮输入提高了土壤中无机氮的含量,缓解了养分限制,进而提高了盐地碱蓬群落地上生物量、盖度、平均株高及频度,最终增强了生态系统CO2吸收能力,其中植被盖度是影响净生态系统CO2交换的最重要生物因子。生态系统CO2交换(NEE)的季节变化则主要与土壤温度密切相关,生态系统CO2吸收能力随土壤温度升高而显著增强,且氮输入强化了温度对盐沼湿地NEE的影响。 (2)氮输入增加显著提高生态系统光合碳输入量和净同化量,其中+20 g N m-2 y-1氮输入水平导致生态系统光合13C净同化量超过200%。增加的光合碳主要以植物地上生物量和SOC的形式存在于植被-土壤体系中。随着氮输入水平升高,植被总生物量不断增大,地上生物量的分配比例也不断增大,而植物地下生物量分配比例和根冠比则不断降低。植物地上、地下生物量对氮输入量的响应效率低于5 g N m-2 y-1时快速降低。氮输入通过提高植物生物量,进而显著提高了土壤中有机碳含量,特别是DOC和微生物生物量碳(MBC)等活性有机碳含量显著升高。 (3)氮输入增加提高了盐沼湿地生态系统土壤CO2和CH4的排放,其中CO2排放通量升高主要表现在生长季,而CH4排放通量升高主要表现在淹水期。氮输入主要通过提高土壤养分含量(铵态氮、硝态氮等)刺激植物生长,从而向土壤中传输更多活性有机碳,如DOC等,进而刺激微生物的代谢活性以产生和排放更多CO2和CH4。土壤CO2排放通量季节变化主要受到温度的控制,随土壤温度升高,土壤CO2排放通量呈指数升高,且氮输入显著抑制土壤CO2排放通量的温度敏感性Q10;土壤CH4的排放通量季节变化主要受到土壤含水量的控制,随土壤含水量升高,土壤CH4排放通量呈指数升高。氮输入提高了土壤CH4排放通量对水分的响应敏感性。 (4)淹水频率是控制盐沼湿地SOC流失的主要因素,而氮输入增加弱化了淹水频率对土壤CO2和CH4排放以及DOC流失的控制作用。提高淹水频率显著抑制盐沼湿地土壤CO2排放、刺激CH4排放。此外,淹水频率升高通过提高物理冲刷作用刺激土壤DOC流失。氮输入抑制了无植被生长的盐沼湿地SOC的流失,这与有植被的盐沼生态系统有所不同,主要归因于无植被输入活性有机碳。模拟月潮汐处理下SOC分解量与土壤DOC流失量呈线性正相关,而模拟半日潮处理下两者没有显著相关性,这是由于土壤DOC在不同淹水频率下的流失途径不同,低频淹水时DOC分别主要以分解形式流失,而高频淹水时DOC主要以淋溶形式流失。 综上所述,氮输入增加显著改变了盐沼湿地碳输入、碳分配和碳排放等碳循环关键过程,同时氮输入还影响了上述碳循环过程与土壤温度、水分动态的相互作用关系。因此,评估盐沼湿地生态系统碳汇功能及其未来变化趋势时,应考虑近岸水体富营养化对盐沼湿地碳循环关键过程的影响,同时还强调周期性潮汐作用与氮输入的耦合作用对碳循环关键过程的影响。这将有助于对未来全球变化过程中盐沼湿地“蓝色碳汇”功能进行预判并提出合理的管理措施。
Other AbstractDue to the high primary productivity, low decomposition rate of soil organic carbon (SOC) and high efficiency in sedimentation of salt marshes, they have great potential in capturing and burying SOC. Thus, these ecosystems are generally considered as important "Blue carbon sinks" on Earth. However, in recent years, under the combined effect of large-scale production and application of chemical fertilizer, fossil fuel combustion and intensive management of animal husbandry, more and more nitrogen (N), especially nitrate nitrogen, enters the marine ecosystem through surface runoff, resulting in the increasing eutrophication of coastal water. N carried by the tide input into a salt marsh ecosystem, which have great uncertainty of the influence on the biogeochemical cycle of organic carbon in a salt marsh ecosystem. Therefore, in this study, we took a salt marsh ecosystem in the Yellow River Delta (YRD) as the research object, through conducting a field experiment of N input and a laboratory experiment of N input coupled with tidal flooding, combining with 13C-CO2 labelling technic. We mainly discussed the responses of key processes of carbon cycle, such as net ecosystem CO2 exchange (NEE), photosynthetic carbon allocation, soil CO2 and CH4 emissions, and dissolved organic carbon (DOC) loss of a salt marsh to different N input levels in the Yellow River Delta, the effects of environmental and biological factors on each process of carbon cycle under N input conditions, and the effect of N input on the control of the inundation frequency on SOC loss. The main results were as follows: (1) N input significantly increased CO2 uptake of ecosystem by 84.06%-220.54%, mainly contributed to the significant increase of CO2 uptake in the growing season with the increasing N input. The increase of CO2 uptake caused by N input was mainly due to the increase of aboveground biomass, coverage, average height and frequency of Suaeda salsa. N input increased the contents of inorganic N in soil, alleviated nutrient stress, thereby stimulated plant growth and improved the ability of ecosystem to absorb CO2. The seasonal variation of NEE was mainly related to soil temperature. NEE decreased significantly with the increasing soil temperature, and N input strengthened the effect of temperature on NEE in a salt marsh. (2) N input significantly increased the input of photosynthetic carbon and net carbon assimilation. The treatment of +20 g N m-2 y-1 increased the net photosynthetic 13C by over 200%. The increased photosynthetic carbon mainly existed in the form of plant aboveground biomass and SOC in the vegetation-soil system. With the increase of N input, the total biomass of plant and the fraction of aboveground biomass increased, while the fraction of belowground biomass and root/shoot ratio decreased. The N response efficiency of plant aboveground and underground biomass was decreased rapidly when the N input level lower than 5 g N m-2 y-1. The increase of plant biomass caused by nitrogen input increased SOC content, especially DOC and microbial biomass carbon (MBC) contents. (3) N input increased soil CO2 and CH4 emissions in a vegetated salt marsh ecosystem. The increase of CO2 emission flux mainly occurred in the growing season, while the increase of CH4 emission flux mainly occurred in the flooding period. N input stimulates plant growth by increasing soil nutrient content (ammonium N nitrate N etc.), so as to transfer more active organic carbon, such as DOC, to the soil, and then stimulate microbial metabolic activity and produce more CO2 and CH4. The seasonal variation of soil CO2 emission flux was mainly controlled by temperature. With the increase of soil temperature, soil CO2 emission flux increased exponentially, and Ninput inhibited the temperature sensitivity Q10 of soil CO2 emission. The seasonal variation of soil CH4 emission flux was mainly controlled by soil water content, and soil CH4 emission flux increased exponentially with the increase of soil water content. Nitrogen input increased the sensitivity of soil CH4 emission flux to water. (4) Inundation frequency is the main factor controlling SOC loss in a salt marsh, while Ninput weakens the control of inundation frequency on the production and emission of soil CO2 and CH4 and DOC loss. With the increasing frequency of inundation, the emission of CO2 was significantly inhibited and the emission of CH4 was stimulated. In addition, the increase of inundation frequency stimulates the loss of DOC by increasing tidal flush. N input inhibited the loss of SOC in this experiment conducted in the salt marsh wetland without vegetation, which was different from that in the salt marsh ecosystem with vegetation, mainly due to the lack of active organic carbon input by plants. There was a positive linear correlation between the decomposition of SOC and the loss of soil DOC under the lunar tide treatment, but there was no significant correlation between the two under the semidiurnal tide treatment. This was due to the different ways of soil DOC loss under different inundation frequencies. DOC was mainly in the form of decomposition and leaching under low and high frequency flooding, respectively. In summary, N input significantly changed the key processes of carbon cycle, including carbon input, carbon allocation and carbon emission. Meanwhile, Nnput also affected the relationships between the carbon cycle and soil temperature, dynamics of soil water and salinity, which was mainly owing to the changes of soil nutrient content and vegetation productivity. In the future, when evaluating the carbon budget and carbon sink function of a salt marsh ecosystem, we should consider the impact of large amount of N nput caused by coastal eutrophication on the key process of carbon cycle, as well as the coupling effect of periodic tidal inundation and N input. This will help to predict the ecological function of "Blue Carbon" sink of salt marsh under global change in the future and put forward reasonable management measures for salt marshes.
Language中文
Document Type学位论文
Identifierhttp://ir.yic.ac.cn/handle/133337/29346
Collection中科院烟台海岸带研究所知识产出
Recommended Citation
GB/T 7714
李隽永. 模拟氮输入对黄河三角洲盐沼湿地碳循环关键过程的影响[D]. 中国科学院烟台海岸带研究所. 中国科学院烟台海岸带研究所,2021.
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