黄河口新生湿地系统碳氮循环关键过程对外源氮输入的响应

The coastal wetland in the Yellow River estuary, formed by the interaction of Yellow River estuary and Bohai sea, is an important ecological type, which acts as an important "sink" of exogenous nitrogen (N) (N deposition and terrestrial N import). In order to evaluate the effects of exogenous N import on the key processes of carbon (C) and N cycles in the new-born wetland, the Suaeda salsa wetland and Phragmites australis wetland in the new-born region are chosen and the key C and N cycling processes, influced by exogenous N, were systemically researched by using 15N isotope technique, acetylene (C2H2) inhibition technique, and static-chamber and gas-chromatography methods. The main goals of this project are:(i) to discuss the influences of exogenous N on the dynamic characteristics of C and N in the plant-soil (water) system, (ii) to determine the response mechanisms of exogenous N on the key transformation processes of C and N in the plant-soil (water) system, (iii) to confirm the effects of exogenous N on the emission of carbon dioxide (CO2), methane(CH4) and nitrous oxide (N2O), and their production mechanisms and 'source/ sink' functions, (iv) to evaluate the influences of exogenous N on the C or N balance and change trend of the new-born wetland, and put forward the regulation measures for maintaining stability and health of the new-born wetland in the Yellow River estuary under the effects of different N import intensities. The results of this project not only can reveal the response mechanism of exogenous N on the key processes of C and N cycles, but also can offer some important scientific gists for the ecological protection and management of the new-born wetland.

黄河口新生湿地是黄河河口与渤海相互作用形成的重要生态类型，是外源氮（氮沉降和陆源氮输入）的一个重要"汇"。为了评估外源氮输入增加对新生湿地碳氮循环关键过程的影响，项目选择新生湿地区的碱蓬湿地和芦苇湿地为研究对象，基于野外观测、微区试验和培养实验，应用15N同位素示踪、乙炔（C2H2）抑制和静态箱-气相色谱等技术，探讨外源氮输入对新生湿地植物-土壤（水）系统碳氮动态特征的影响，揭示新生湿地植物-土壤（水）系统碳氮转化关键过程对外源氮输入的响应机制，明确外源氮输入对新生湿地CO2、CH4和N2O释放规律、生成机制及"源/汇"功能的影响，评估外源氮输入强度对新生湿地碳氮循环平衡状况及变化趋势的影响，提出不同氮输入强度下维持新生湿地系统稳定与健康的调控措施。研究结果不仅可深入揭示新生湿地碳氮循环关键过程对外源氮输入的响应机理，而且还为新生湿地的生态保育与管理提供重要科学依据。

为了深入理解外源氮输入对黄河口新生湿地碳氮循环关键过程的影响，项目探讨了外源氮输入对湿地土壤碳氮时空分布及植物氮累积与释放过程的影响，揭示了氮输入影响下湿地温室气体释放规律及其生成机制，评估了氮输入强度对湿地氮循环平衡状况的影响。研究表明：（1）外源氮输入并未改变湿地土壤TN和NH4+-N的变化模式，但明显改变了SOC和NO3--N的动态特征；适量氮输入明显提高了土壤中NO3--N含量，但持续输氮不利于SOC转化。（2）外源氮输入条件下湿地土壤矿化速率和累积矿化量均发生了明显改变，低氮输入土壤的矿化能力最低，高氮输入最高，而中氮输入土壤的矿化量较高且最为稳定。（3）外源氮输入并未改变植物地上生物量的季节变化模式，但改变了其地下生物量的动态变化特征；外源氮输入不但延长了植物生长高峰期，而且也使得地上生物量最大值取得时间推迟20 d左右；氮输入并未改变植物不同器官的氮累积分配格局以及地上与地下之间的养分供给关系，但其为适应不同养分条件而调整自身养分供给与分配的特性在中氮输入下尤为明显。（4）外源氮输入条件下残体基质质量改变促进了其分解，且该促进作用在低氮处理下最为明显；氮输入条件下残体中的氮在分解过程中呈累积状态，且累积量随氮输入增强而增加。（5）不同氮输入强度下湿地均表现为较强的CO2和N2O释放源；氮输入整体抑制了CO2和N2O释放，且该抑制作用在低氮和高氮处理下较强。湿地土壤有机碳矿化速率 (CO2释放) 及CH4产生与氧化能力受温度、水分及碳氮基质等因素的影响。特别是N输入（NH4+、NO3-）类型与强度对不同潮滩湿地土壤CH4产生与氧化的促进/抑制程度差异显著。未来氮输入量增加情况下, CO2、CH4和N2O的源功能将明显增强。（6）建立了不同氮输入强度下湿地氮循环分室模式，定量确定了各分室氮储量及流通量，并指出：当湿地氮养分水平较低时，可适当增加湿地氮养分，并使其维持在中等氮水平；当湿地氮养分达到很高水平时，应采取有效养分削减措施以维持湿地系统的稳定与健康。