典型滨海湿地反硝化与硝态氮氨化耦合的干湿交替驱动机制

Coastal wetlands have being increasingly concerned, particularly in sediment nitrogen transformation and corresponding environmental impacts under global climate changes and artificial accelerated disturbances. Simultaneous investigation to a coupled processes, denitrification and nitrate ammonification, is a key method of studying variations and environmental effects of nitrogen reduction. Chongming east intertidal flat, a typical coastal wetland near the entrance of Yangzi River to the East China Sea is employed to define variations of both denitrification and nitrate ammonification under the unique physical drying and re-flooding cycles driven by periodic tidal movements and different vegetations. Using methods of in-situ and sediment core incubations, strenghth of the two processes are investigated by 15N isotope dilution technique under repeated natural and simulated spring and semi-diurnal tides, and continuous waterflooding with 4 types of vegetation (Phragmites australis, Spartina alterniflora and their symbiosis systems, and no vegetation) during 4 seasons, respectively. The effects of plant harvest are also to be deliberately estimated. With the aids of isotope ratio mass spectrometer, PCR-DGGE and soil enzyme techniques, changes in contents, ratios and fraction of carbon and nitrogen substrates, structures and diversity of microbial communities, and potential activities and Km, Vmax parameters of N-related soil extracellular enzymes in sediments are used to uncover mechanisms and relations of denitrification and nitrate ammonification. Our project would substantially enhance the understanding of nitrogen reductions in coastal wetlands and provide theoretical and practical inspirations for impartially understanding and evaluating the environmental effects of denitrification and nitrate ammonification.

全球气候变化及人为活动加速影响下，滨海湿地氮素转化及其环境影响备受关注。同步研究反硝化与硝态氮氨化的变化特征并揭示其机制是评估湿地氮素还原之环境影响的重要方法。以长江入海口典型滨海湿地- - 崇明东滩为研究对象，围绕潮汐驱动下的干湿交替过程以及湿地覆被差异，通过原位试验与土柱模拟相结合的方法，采用15N稀释法，研究半月潮、日潮及持续淹水过程沉积物反硝化与硝态氮氨化强度的变化特征，分析干湿交替循环的影响；研究芦苇、芦苇-米草交错带、米草和光滩覆被类型在春夏秋冬季节沉积物反硝化与硝态氮氨化强度的变化特征，分析植被收割的影响。借助同位素质谱、PCR-DGGE以及土壤酶等技术，从沉积物碳氮形态、含量及比例，微生物群落结构与多样性，氮还原相关胞外酶活性及其表观酶促反应动力学参数（Km、Vmax）等，多层次揭示两个还原过程的耦合机制。项目研究是正确认识和科学评估滨海湿地氮素还原之环境影响的迫切需要与基础。

全球气候变化及人为活动加速影响下，滨海湿地氮素转化及其环境影响备受关注。同步研究反硝化（Den）与硝态氮氨化（DNRA）的变化特征并揭示其驱动机制对湿地氮素还原之环境影响评估而言显得十分必要。以长江入海口典型滨海湿地——崇明东滩为对象，围绕潮汐驱动下的干湿交替过程以及湿地覆被差异及其管理，通过原位试验与土柱模拟相结合的方法，采用15N稀释法，研究湿地土壤Den与DNRA相对重要性特征及机制。结果表明，.（1）半月潮干湿交替过程中，DNRA/Den随着含水率的降低（65 %-3 %）而升高，从1.0（含水率65 %）升至2.9×105（含水率3 %）。沉积物中的微生物主要以Proteobacteria(变形菌门)、Bacteroidetes(拟杆菌门)、Firmicutes (硬壁菌门)、Gemmatimonadetes(芽单胞菌门)以及Actinobacteria(放线菌门)为优势菌群。这表明，崇明东滩湿地干湿交替过程沉积物中的NO3--N倾向以DNRA途径还原为NH4+-N。.（2）冬季时节，互花米草植被带沉积物Den强度高达0.2 g/(m2•d)（以20 cm土层，1.35 g/cm3容重计），显著高于其他植被类型。因此，冬季可能是互花米草植被带沉积物氮素Den逸失高峰期。从植被调控策略而言，减控互花米草有利于湿地N2O排放的减少。.（3）湿地沉积物C/N增加30%（添加C6H12O6），光滩、互花米草、互花米草-芦苇交互带、芦苇带沉积物Den强度分别低于对照（原土，无添加）27、9、1、8倍。这表明，沉积物C/N升高有望显著控制Den过程相关温室气体的排放。.（4）无论C/N增加还是降低（±30%），不同植被类型下沉积物DNRA强度均显著低于对照(P<0.05)。这表明，滨海湿地“高碳低氮”大背景下，短期的偏离沉积物常态背景C/N的改变（±30%）均会降低沉积物DNRA强度。.（5）冬季收割芦苇使沉积物N2O的释放增加，相比较而言，收割互花米草则显著降低沉积物N2O的释放。当温度升高10℃时，芦苇收割并没有增加N2O的释放，但互花米草沉积物N2O的释放增加。由此可见，未来温度升高可能会改变沉积物氮素还原途径及强度。