• 关键词：水生维管束植物  通气组织  N₂O  N-15示踪技术  硝化反硝化

• 基金项目：国家自然科学基金（No.41571458，41301517，41471415）；江苏省农业科技自主创新项目（No.CX（14）2093）；江苏省科技支撑计划项目（No.BE2013436）；公益性行业（农业）科研专项（No.201203050）

• 高岩
• 江苏省农业科学研究院农业资源与环境研究所, 南京 210014

• 张芳
• 江苏省农业科学研究院农业资源与环境研究所, 南京 210014

• 刘新红
• 江苏省农业科学研究院农业资源与环境研究所, 南京 210014

• 易能
• 江苏省农业科学研究院农业资源与环境研究所, 南京 210014

• 王岩
• 江苏省农业科学研究院农业资源与环境研究所, 南京 210014

• 张振华
• 江苏省农业科学研究院农业资源与环境研究所, 南京 210014

• 严少华
• 江苏省农业科学研究院农业资源与环境研究所, 南京 210014

• 摘要：漂浮水生维管束植物具有发达的通气组织，然而关于其传输水体中产生温室气体N₂O方面的研究还很匮乏.本研究以漂浮水生植物凤眼莲为代表，利用稳定氮同位素示踪技术，设计能够分隔根室和叶室的水生植物生长系统，通过微宇宙实验定量追踪N-15标记的氮素在凤眼莲根系介导下的转化途径、N₂O产生规律及N₂O通过通气组织向空气的传输过程.研究结果表明，加入水体的¹⁵NO₃^-有少部分通过异化还原成为铵（DNRA）过程转化为NH₄⁺-¹⁵N，主要通过反硝化反应生成N₂O；加入的¹⁵NH₄⁺主要发生了耦合硝化-反硝化反应.种植凤眼莲均使叶室中N₂O-¹⁵N原子百分超和¹⁵N₂O浓度明显高于无植物的对照，一方面说明凤眼莲根系能够促进反硝化、硝化-反硝化反应过程，同时也说明水体中的¹⁵N₂O有相当一部分通过植株体传输到空气中.凤眼莲通气组织主要通过分子扩散从高浓度空间向低浓度空间输送¹⁵N₂O.在标记NO₃^--¹⁵N的水体中，凤眼莲在前期促进了¹⁵N₂O向顶空排放，但并未在整个生长期持续促进N₂O释放.在标记NH₄⁺-¹⁵N的水体中，植株体富集是NH₄⁺-¹⁵N的一个主要归趋途径，但同时也有部分NH₄⁺-¹⁵N转化为N₂O通过植株通气组织持续、缓慢地释放到顶空当中.研究结果阐明了漂浮植物对水体氮转化过程及N₂O输移途径的调节作用，可为全面理解水体生态系统氮循环过程提供理论基础.

• Abstract：The aquatic vascular plants, including free-floating plants, have well-developed vascular tissues. However, little is known about the transportation of N₂O, produced from the biological nitrogen transformation process in water, via the vascular tissues of the free-floating plants. In this study, water hyacinth was used as a representative for free-floating plant. In order to distinguish between two N₂O diffusion sources (i.e. coming from water and from the vascular tissues), a plant growth system that can separate the root compartment from the aerial compartment was designed. The stable isotope N-15 tracing method was used to investigate the fate of N in water with or without growth of water hyacinth using microcosm experiments, including the transformation of N-15 in water, the production of ¹⁵N₂O and the transfer of ¹⁵N₂O via vascular tissues of water hyacinth. The results show that dissimilatory nitrate reduction to ammonium (DNRA) process occurred in water with addition of ¹⁵NO₃^- although a large proportion of ¹⁵NO₃^- was transformed via denitrification. The coupled nitrification and denitrification was the major process for biological transformation of ¹⁵NH₄⁺ in water. N-15 excess percentage of N₂O and ¹⁵N₂O concentrations in the headspace of aerial apartment from treatments with water hyacinth were significantly higher than those without water hyacinth, indicating that the roots could promote the denitrification of NO₃^--¹⁵N and nitrification/nitrification-denitrification of NH₄⁺-¹⁵N to produce ¹⁵N₂O. This could also illustrate that a large proportion of ¹⁵N₂O produced in water would diffuse into air via the aerating tissues of water hyacinth. In water with NO₃^--¹⁵N, the growth of water hyacinth could only promote the ¹⁵N₂O emission during the early stage of incubation, while relatively slow and continuous emission of ¹⁵N₂O via the aerating tissues were observed in water with NH₄⁺-¹⁵N during the whole experimental period. In addition, plant assimilation was one of the major fates of NH₄⁺-¹⁵N in water. The results could help to elucidate the role of free-floating aquatic plants in mediating the production and transportation of gaseous nitrogen in eutrophic water, providing the theoretical basis for comprehensive understanding of nitrogen cycling process in aquatic ecosystem.

• Key words：aquatic vascular plants  aerating tissue  N₂O  N-15 tracing method  nitrificantion and denitrification

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