闽江河口湿地CH4和N2O释放对氮输入增加与互花米草入侵交互作用的响应

Nitrogen addition, exotic species invasion and global climate change are important research contents of the global change. Coastal region, acts as the important "sink" of terrestrial nitrogen, has significant effects on the global climate. How does its greenhouse gas emission respond to the double effects of increasing nitrogen input and exotic plant invasion? The native Cyperus malaccensis and invasive Spartina alterniflora salt marshes, located in the Min River estuary, are selected as study objects, and the effects of nitrogen addition on CH4 and N2O emission will be studied for three years based on the field experiment and control experiment. The main goals of this project are (i) to discuss the effect of exogenous nitrogen input and Spartina alterniflora invasion on CH4 and N2O flux characteristics and "source/sink" function. (ii) to study the temporal variability of CH4 and N2O emission as affected by the nitrogen addition. (iii) to confirm the effect and contribution of plant in the process of CH4 and N2O emission as affected by the nitrogen addition.(ⅳ) to reveal the responses of CH4 production and oxidation processes to the nitrogen input in the native and invasive wetland soils. (v) to evaluate the contributions of nitrification, denitrification, nitrifier denitrification and other process on CH4 and N2O emission in response to the nitrogen input. The results of this project not only has important theoretical significance for the further understanding of carbon, nitrogen biogeochemical processes in the native and invasive estuarine wetlands as affected by exogenous nitrogen input, but also can offer important scientific base which is propitious to the restoration and management of degraded wetland caused by the Spartina alterniflora invasion.

氮输入增加、外来生物入侵与温室效应引起的全球气候变化是当前全球变化研究的重要内容。滨海河口湿地作为陆源氮的一个重要"汇"区，其温室气体排放如何应对氮输入增加与外来植物入侵的双重影响？本项目选择闽江河口短叶茳芏湿地和互花米草入侵湿地为研究对象，基于野外原位实验和室内控制实验，通过连续3年的研究，探讨外源氮输入和互花米草入侵对河口湿地CH4和N2O通量特征及"源/汇"功能的影响，研究氮输入对湿地CH4和N2O排放影响的时间变异性，明确氮输入影响下湿地植物对CH4和N2O排放的影响及贡献，揭示天然与入侵湿地土壤CH4产生与氧化过程对氮输入的响应，定量评估氮输入及互花米草入侵影响下硝化作用、反硝化作用、硝化细菌反硝化作用及其他过程对N2O 排放的贡献。研究结果对于深入理解外源氮输入和互花米草入侵影响下河口湿地碳、氮生物地球化学过程具有重要的理论意义，并可为互花米草入侵湿地的恢复与治理提供科学依据。

项目以闽江河口短叶茳芏湿地为研究对象，基于野外原位实验和室内控制实验，探讨氮输入和互花米草入侵对湿地CH4和N2O释放的影响。结果表明：氮输入对湿地N2O排放的影响具有显著的短期时间变异性，而对CH4排放的短期影响并不明显。在较长时间尺度上，闽江河口湿地总体表现为CH4的排放源和N2O的弱源/弱汇。氮输入促进了短叶茳芏和互花米草湿地的N2O排放，分别比对照增加了136.73%和24.23%。氮输入对短叶茳芏和互花米草湿地CH4排放具有一定的抑制，分别比对照降低了39.24%和1.01%。互花米草入侵并没有显著影响湿地的 N2O排放，但增加了湿地CH4排放，平均比短叶茳芏湿地高了74.85%。湿地CH4排放通量与温度、EC等具有一定相关性，而N2O的排放与气温、地温、EC、pH等环境因子的相关性较弱。植被对CH4和N2O通量具有重要影响，割除植被后N2O通量低于割除植被前，而割除植被后CH4通量在不同处理间规律不同。互花米草入侵能够显著提高湿地土壤的CH4产生潜力，氮输入对两种湿地土壤的CH4产生潜力影响显著，外源氮输入引起的土壤DOC和矿质氮含量以及EC的变化是导致CH4产生潜力变化的重要原因。氮输入对湿地土壤CH4氧化潜力的影响与外源氮的浓度和类型有关，且盐分和氮输入对湿地土壤CH4氧化速率存在一定的交互影响。硝化细菌反硝化作用是短叶茳芏和互花米草湿地土壤N2O产生的关键过程，对湿地N2O排放的贡献不容忽视。硝态氮输入主要通过促进反硝化作用和其他过程从而促进了两种湿地土壤的N2O总生产。铵态氮输入对短叶茳芏湿地土壤N2O产生过程的影响与氮浓度有关，不同浓度铵态氮均通过促进硝化细菌反硝化作用和其他过程从而促进了互花米草湿地土壤的N2O产生，但显著低于硝态氮的促进作用。