互花米草入侵生境中红树植物更新动态与生长适应策略

Intertidal mangrove forests occur on tropical and subtropical shorelines, and support ecosystem goods and services. Cordgrass (Spartina alterniflora) was introduced to China from the USA in 1979. It grows vigorously in China and has spread over much of the Chinese coast, mixed with mangroves in the south. Sonneratia apetala (keora), was introduced to China in 1985 from Bangladesh. Because of its higher survival and growth rate compared to native mangrove species, S. apetala has been used for mangrove restoration and afforestation in China. However, the potential invasiveness of the exotic S. apetala is of concern. The invasion of S. alterniflora has influenced the growth and regeneration of native mangroves over the past two decades, while S. apetala has naturally dispersed into the dense monoculture of S. alterniflora meadows within recent few years. This provides opportunities to study the community dynamic and succession of the ecotone between mangroves and S. alterniflora for understanding the responses of coastal wetland vegetation to global change..In this project, we will choose the exotic mangrove and native mangrove species as comparison study, and focus on the establishment of their seedlings during the stage of early growth. We will experimentally manipulate shade to evaluate the morphological and physiological responses of different mangrove species in order to understand how S. apetala adapt to the low light intensities and maintain its fast growth strategy. We will conducting field manipulate experiments, in order to quantify the above- and below-ground competition between S. alterniflora and mangrove seedlings, as well as the relative contributions and underlying mechanisms of above- and below-ground competition between species, then will estimate the influence of varied mangrove species to the interaction strength and direction between S. alterniflora and mangrove seedlings. We will manipulate with and without competition from S. alterniflora at field sites to investigate the growth and interactions between transplanted mangrove seedlings and S. alterniflora along latitudinal gradient, concurrently document the propagule dispersal, seedling establishment, and sapling growth of mangroves, in order to understand how the mechanisms maintaining the mangrove-Spartina ecotone are affected by biotic and abiotic factors, and to predict how this ecotone is likely to change in the future..By comparing the species traits, interspecific interactions, and abiotic conditions between exotic and native mangrove species, we will seek to understand why the growth and dynamics of the interaction between S. alterniflora and mangroves are proceeding so differently between exotic and native mangrove species, identify the main drivers for community succession in the intertidal zones, and predict the future status of the mangrove-Spartina ecotones along the coast of southern China. The results of this study will provide scientific support for ecological and environmental conservation, as well as shedding insight into how these vital habitats will respond to global change.

互花米草入侵中国东南沿海红树林，抑制乡土红树植物更新，但外来速生红树植物无瓣海桑能够在互花米草入侵生境中实现自然更新。这为研究全球变化下“红树林——互花米草生态交错带”的群落动态过程与演替提出新的科学问题。本项目选择乡土和外来红树植物，聚焦幼苗早期建立这一关键阶段，采用遮荫控制实验，对比不同红树植物对光照变化的形态和生理响应，揭示无瓣海桑在低光下维持快速生长的生物学特性和适应策略；通过野外地上与地下竞争控制实验，研究互花米草和红树植物之间相互作用的过程和机制，阐明地上和地下竞争的相互关系，分析红树植物种类的改变对种间相互作用方向和强度的影响；进一步沿大尺度纬度梯度，研究红树植物的更新生长对温度变化的响应，结合野外固定样地的长期观测，辨析红树植物更新的主要限制因子，预测互花米草和红树林的竞争格局和植被演替趋势。研究结果可为应对滨海湿地生物入侵提供理论基础，为我国红树林保护和恢复提供科学依据。

滨海湿地极易被外来生物入侵。外来入侵植物互花米草侵占我国东南沿海，显著抑制乡土红树植物更新。但外来红树植物无瓣海桑可在互花米草生境中自然扩散，多物种入侵下，正逐渐改变中国东南沿海滨海湿地植被分布格局。.项目组采用现场调查结合无人机航拍，监测东南沿海红树林区互花米草的入侵动态，结果表明：互花米草和乡土红树植物生态位重叠，虽然致密的红树林内无互花米草生长分布，但互花米草比乡土红树植物更耐淹水，在光滩前沿低潮位仅有互花米草的分布。.项目组选择互花米草入侵生境开展野外地上与地下竞争控制实验，结果表明：互花米草丛中红树植物幼苗的更新生长受互花米草地上和地下竞争的抑制，并随物种和时间而变化。乡土红树植物难以在互花米草丛更新，但外来种无瓣海桑有可能成功更新。.项目组进一步开展乡土和外来红树植物幼苗野外移植实验，结合遥感影像分析，结果表明：不同纬度研究地点、不同植被生境，外来种无瓣海桑均比乡土红树植物生长迅速、适应性强。特别是在低纬度地区，无瓣海桑快速扩散，侵入并取代互花米草和乡土红树林。随着外来种互花米草、无瓣海桑的快速扩散，多物种的入侵将改变中国东南沿海潮间带植物的竞争和演替过程。.为深入了解互花米草的入侵特性，项目组在入侵地和原产地开展全境性研究，沿大尺度纬度梯度开展野外现场观测，并结合同质种植园实验，系统对比原产地和入侵地互花米草生活史性状（种子萌发、营养生长、有性繁殖、物候等）在不同地理区域之间以及沿纬度梯度的性状差异，结果表明：入侵地中国互花米草已发生快速适应进化，其在野外和温室同质种植园中都比原产地美国的植株高大、密集、生物量和结实率高。.本项目的研究结果，可为预测外来植物和乡土红树林的竞争格局和植被演替趋势，应对滨海湿地生物入侵提供理论基础，并为我国红树林保护和恢复提供科学依据。