珠江口湿地氮循环及其对环境胁迫的响应

For wetlands of mangrove and Spartina alterniflora in Pearl River Estuary, by establishing the field plots and simulated wetland experiments in greenhouse, this propsal takes the wetland system in its entirety, to quantitative analysis the subsidence of nitrogen in air or input amount of 15N to the ecosystem, by using the stable isotope 15N to study the changes of nitrogen transportation and partition in subsystems of sediment, pore water, presentative plants and animal, including the sediment nitrification and denitrification with microbe activity, which affactted by climate changes (especilly drought and salty tide), and output of nitrogen from the ecosystem (greenhouse gas N2O), to campare the process of nitrogen cycle in nature field plots and artificial simulated system in greenhouse, to reveal the responses and adaptations for alien species of Sonneratia apetala, Spartina alterniflora, and native species of Avicennia marina, and Bruguiera cylindrica, snails and shells, also the process of biogeochemistry of wetland sediment to the stress environmental factors of drought and salty tide. The aims of this proposal are to cetify that the hypothesis of the ecological factors of drought and salty tide maybe affact the nitrogen cycle by impacting the physi-chemical characteristics of sediment and the development of organisms, and then result in the degradation or block the development of coastal wetlands. To study the potential damage of alien plant species on native ecosystem is good for explaining the degradation process and driving machinsm, give some data for reservation and sustanitable development of coastal wetlands, and is also helpful for knowing the globe climate changes and environmental effects.

以珠江口红树林和互花米草湿地为对象，把湿地系统作为整体，通过建立野外样地和温室模拟潮汐湿地，定量分析大气氮沉降或人工施15N迁入，采用稳定15N同位素稀释法研究底泥、孔隙水、代表动植物等组分受气候变化（干旱、咸潮）联合胁迫的氮迁移与分配（含微生物作用的底泥硝化-反硝化）,以及系统中氮的迁出（温室气体N2O排放），比较野外自然系统和温室模拟系统的氮循环过程，并研究外来种无瓣海桑和互花米草、本地种白骨壤和木榄、贝类螺类及其湿地底泥的生物地球化学进程对逆境联合胁迫的响应和适应性。以期证明干旱和咸潮等因子可能因影响底泥物理化学性质、生物的生长发育而影响湿地氮循环过程，进而导致海岸湿地退化或发育受阻的假设。研究外来植物对本地生态系统的潜在危害，有助于阐明湿地的退化过程和驱动机制，为海岸湿地的保护和可持续发展提供科学依据，对进一步了解全球气候变化与环境效应具重要意义。

全球气候变化导致干旱和咸潮在珠江口频繁发生，沿海红树林等生态系统的氮素循环过程是否受它们显著的影响？同时，外来植物的生态危害日趋严重，本地红树植物与它们的竞争关系如何？为此，本项目研究了珠江口湿地（珠海淇澳和广州南沙湿地）在干旱和咸潮胁迫下的生态学过程，结合野外监测和温室模拟湿地系统调控数据，探讨了本地红树植物湿地的退化机制。.①温室中的互花米草湿地，温室气体N2O的排放通量与气温表现出正相关，与相对湿度负相关。②外来入侵植物互花米草在珠海淇澳的生长已显著改变了生境中的某些化学因子，如导致表土上部pH显著下降、Eh显著高于本地种桐花树湿地等，为此应严格控制其草生长范围。南沙湿地中，外来红树植物无瓣海桑和拉关木生长迅速，可能因加快了有机质分解与物质循环过程，导致底泥部分因子（如pH、Eh值等）发生明显改变。③珠海淇澳湿地底泥的δ13C和δ15N值高于南沙湿地底泥的相应值。对于δ15N值，淇澳的互花米草（平均8.26‰）和无瓣海桑（9.35‰）均显著高于本地种桐花树（6.16‰）和卤蕨（5.69‰）。南沙的无瓣海桑（3.78‰）和拉关木（5.56‰），也显著高于桐花树（2.26‰）和卤蕨（2.01‰），提示这3种外来植物的δ15N在植物体内的贮存利用上与本地2种红树植物有显著区别，可能导致了海岸湿地生态过程和生物地球化学循环的改变。④互花米草根只有初生结构，具发达的外皮层和皮层通气组织，内皮层细胞壁五面加厚明显，且随盐度的升高呈先增大后减小的趋势；中柱鞘细胞壁也出现加厚现象，该结构体现出对盐浸环境的适应性。无瓣海桑叶片中脉维管束具微弱形成层，叶脉维管组织比海桑更发达；贮藏组织中含单宁细胞、晶体细胞较多；栅栏组织含叶绿体多于海桑等特点，因而对不利的生长环境具更强的适应性。无瓣海桑生长迅速，林冠郁闭，导致本地红树植物秋茄等生长受限，且它能自然繁殖更新，提示无瓣海桑存在生态入侵风险，建议在沿海地区不再种植。