黄河三角洲湿地是典型的滨海湿地，处于海陆相互作用地带，是全球环境变化的缓冲区，是响应全球变化和人类活动较为敏感的生态系统之一。滨海湿地是海岸带一个非常重要的生态类型，承接来自陆地人类活动带来的大量含氮物质，其在净化环境、减轻灾害、保护海岸线和维持生物多样性中发挥着重要作用。黄河三角洲滨海湿地生态系统中氮素的生物地球化学过程十分复杂，其不但影响湿地生态系统本身的调节机制，而且在环境介质中的特殊动力学过程与一系列全球环境问题息息相关。因此，加强滨海湿地基础研究对于合理开发利用和保护滨海湿地具有重要的现实意义。为了更深入的了解黄河三角洲滨海湿地氮的生物地球化学循环特征及其关键机制，本研究以黄河三角洲两种优势植物（芦苇和盐地碱蓬）作为研究对象，通过野外样品采集、原位试验、盆栽试验和室内试验，研究了黄河三角洲地区大气干、湿沉降中氮素的季节变化、湿地土壤氮的季节变化与化学转化特征，探讨了湿地优势植物生物量与氮累积季节变化特征、添加氮素的利用率、湿地土壤微生物生物量氮的季节变化、湿地植物残体分解及分解过程氮动态特征，主要结论如下：（1）黄河三角洲地区氮沉降具有明显的季节性，其中69%集中在降雨量较丰沛的6至8月。湿沉降输入的氮素约占总沉降量的67.98%。大气硝态氮沉降与铵态氮沉降对表层0-10 cm土壤硝态氮与铵态氮的月平均贡献率分别为31.38%和20.50%，表明大气氮沉降是黄河三角洲滨海区域土壤主要氮素来源之一。（2）黄河三角洲滨海湿地芦苇和盐地碱蓬群落区表层土壤（0~10 cm）无机氮库具有明显的季节变化特征，其中全氮的变化范围分别介于305.81 ± 47.60~652.61 ± 51.58 μg·g^-1、351.85 ± 50.85~572.91 ± 62.20 μg·g^-1。（3）两种优势植物群落区土壤氮的净矿化/硝化速率、总矿化/硝化速率均呈波动变化，5~10月的植物生长季中，两群落区土壤氮的净矿化量、净硝化量、总矿化量、总硝化量分别为5.92 g·m^-2、6.40 g·m^-2、1222.39 g·m^-2、1874.57 g·m^-2和2.67 g·m^-2、6.56 g·m^-2、1843.51 g·m^-2、1744.18 g·m^-2，表明净矿化/硝化速率仅仅能显示出一小部分矿化/硝化作用的真实速率。（4）两种试验植物不同器官和总生物量均具有明显季节变化特征，且均符合抛物线模型，但每种植物三种水位处理之间各器官和总生物量之间的差异均未达到显著水平（p>0.05）。（5）三种水位处理的芦苇根的氮累积量均高于其他器官，说明芦苇储存氮素的主要器官是根，而三种水位处理的盐地碱蓬叶的氮累积量最高，说明叶是盐地碱蓬储存氮素的主要器官。（6）添加的¹⁵N在三种水位处理的芦苇各器官中的分配均表现为：叶>根>茎，而其在三种水位处理的盐地碱蓬各器官中的分配均表现为：叶>茎>根。芦苇盆栽试验中，添加的¹⁵N的损失率较高，均超过60%，而盐地碱蓬盆栽试验中，添加的¹⁵N的损失率在40%左右。（7）芦苇群落区与盐地碱蓬群落区土壤微生物生物量碳与生物量氮均存在明显的季节变化。植物生长季内，芦苇群落区表层土壤（0~10 cm）微生物量氮介于11.22~236.27 μg·g^-1之间，盐地碱蓬群落区表层土壤微生物量氮介于6.74~76.80 μg·g^-1之间。（8）芦苇和盐地碱蓬残体各器官的失重率和分解速率均存在明显的季节变化，差异均达到显著水平（p<0.05），分解速率受初始C/N的影响，两种湿地植物残体各器官的干物质残留率均符合单项指数模型。（9）芦苇和盐地碱蓬植物残体分解过程中各器官TN含量呈明显的季节变化趋势，C/N的变化大体呈现出与全氮含量相反的特征，两种植物各器官在整个试验期间大部分时间里NAI值小于100%，即各器官在分解过程中主要表现为氮的释放。

The Yellow River Delta wetland is typical costal wetland, which located in the interactive areas between land and sea. It is the buffer zone of global environmental change. It is a very important ecosystem, which is sensitive to the global chang and human activities. As an important ecosystem in coastal zone, costal wetlands undertake a large number of nitrogenous compounds form terrestrial human activities, and play an important role in cleaning up the environment, mitigating disaster, protecting the coastline and maintaining biological diversity. Biogeochemical process of nitrogen in the Yellow River Delta wetland ecosystem is enormously complex. It not only affect regulation mechanism of wetland ecosystem, but also the special kinetics process occurred in environmental medium is closely correlated with a series of global environmental problems. Therefore, the basic research of coastal wetlands is great important for developing and protecting coastal wetlands. In this work, two dominant plants (Phragmites australis and Suaeda salsa) in the Yellow River Delta were selected as study objects in order to understand the nitrogen biogeochemical cycle rule and its key mechanism. The field sample collection, in-situ and lab test, pot experiment were performed to study the monthly variation of wet and dry atmospheric nitrogen depositions, the monthly variation and transformation characteristics of nitrogen in wetland soil, the seasonal dynamics of dominant plants biomass and nitrogen accumulation, the efficiency of adding nitrogen, the seasonal dynamics of microbial biomass nitrogen in wetland soils，the litter decomposition rules and nitrogen dynamics in decomposition process. The main results were drawn as follows：(1) The atmospheric nitrogen deposition had significantly seasonal dynamics, and 69% of it occurred in rainy season (from June to August). The main form of atmospheric nitrogen input was wet deposition which accounted for 67.98% of the total atmospheric nitrogen deposition. The average monthly attribution rate of atmospheric deposition of NO₃^--N and NH₄⁺-N were about 31.38% and 20.50% for the contents of NO₃^--N and NH₄⁺-N in 10 cm soil layer , respectively. Therefore, the atmospheric nitrogen was one of main sources for soil nitrogen in coastal zone of Yellow River Delta. (2) The inorganic nitrogen of topsoil (0~10cm) in Phragmites australis and Suaeda salsa communities zones in the Yellow River Delta had significantly seasonal dynamics. The TN of two communities zones were 305.81 ± 47.60~652.61 ± 51.58 μg·g^-1, 351.85 ± 50.85~572.91 ± 62.20 μg·g^-1, respectively. (3) The soil nitrogen net mineralization/nitrification rates and gross mineralization/nitrification rates in two community’s zones presented significant fluctuations. In the growth season (from May to October), the nitrogen net mineralization and nitrification amounts, gross mineralization and nitrification amounts in soil of two communities zones were 5.92 g·m^-2, 6.40 g·m^-2, 1222.39 g·m^-2, 1874.57 g·m^-2 and 2.67 g·m^-2, 6.56 g·m^-2, 1843.51 g·m^-2, 1744.18 g·m^-2, respectively. Hence, net mineralization/nitrification rates reveal only a small fraction of the true rate of mineralization/nitrification. (4) The biomass in different organs and the total biomass of two species had significantly seasonal dynamics, and they could be described by parabolic model. But no significant differences among the biomass in different organs and the total biomass of each species in three different water tables were noted (p>0.05). (5) The accumulative nitrogen amount in roots of Phragmites australis was higher than it in other organs. It suggested that root was the important organ to keep nitrogen. In contrast, the accumulative nitrogen in leaves of Suaeda salsa was highest, suggested that leaf played a key role in storing nitrogen. (6) The distribution of the adding ¹⁵N in leaf of Phragmites australis in three water tables was highest, followed by roots, stems. But the distribution of the adding ¹⁵N in leaf of Suaeda salsa in three water tables was highest, followed by stems, roots. The rate of added ¹⁵N loss was higer in pot experiment of Phragmites australis, and it was more than 60%. In pot experiment of Suaeda salsa, the rate was about 40%. (7) The microbial biomass carbon and nitrogen both had significantly seasonal dynamics in two community’s zones soil. In the plant growth season, the MBN in topsoil (0~10 cm) of two community’s zones were 11.22~236.27 μg·g^-1, 6.74~76.80 μg·g^-1, respectively. (8) There were significantly seasonal dynamics of weightlessness rates and decomposition rates of two dominate plants litter and achieved significant differences (p<0.05). The decomposition rate was greatly affected by initial C/N. The residual rate of dry matter could be described by single exponential model. (9) The significantly seasonal dynamics of TN content of different organs litter in decomposition process appeared, and the variation trend of C/N and TN content presented opposite character. In most of study period, NAI of two plants different organs were less than 100%, indicated that the nitrogen release was the dominant process in decomposition process of different organ litters.