红树林和互花米草相互作用对环境变化的多尺度响应

Coastal wetlands provide a variety of important services to humans, including protecting the shoreline from storms, cleaning waters, and supporting fisheries. In China, coastal wetlands are dominated by exotic Spartina alterniflora along almost the entire coast, mixed with mangroves in the south. In the United States, a similar geographic pattern occurs where S. alterniflora is native. The ecotone between mangroves and S. alterniflora is affected by climate change and human impacts, and therefore provides a useful study system for understanding the responses of coastal wetland vegetation to global change and anthropogenic impacts. In order to protect and restore mangrove wetland in China, there is an urgent need to understand the patterns and mechanisms of S. alterniflora invasion and the subsequent ecological effects of S. alterniflora on the native mangrove ecosystem..In this project, we will study the mechanisms by which mangroves and S. alterniflora interact across three different spatial scales (latitudinal, estuarine and intertidal gradient). We will manipulate with and without competition from S. alterniflora at field sites, or within elevation platforms (containing mesocosms at different elevations that manipulate elevations at a single point in an attempt to isolate the effect of hydroperiod from other variables) to investigate the growth and interactions between transplanted mangrove seedlings and S. alterniflora along different environmental gradients (temperature, salinity, and vertical elevation) 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. .Concurrently, we will document the propagule dispersal, seedling establishment, and sapling growth of mangroves with and without competition from S. alterniflora at field sites in order to disentangle the roles of dispersal limitation and habitat limitation due to competition from S. alterniflora on establishment success of mangroves. By comparing the species traits, interspecific interactions, and abiotic conditions between China and US, we will seek to understand why the dynamics of the interaction between S. alterniflora and mangroves are proceeding so differently in the US and China, identify the main drivers for invasion, and predict the future status of the mangrove-Spartina ecotones of these two regions..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.

互花米草在中国（入侵地）和美国（原产地）均与红树林共同形成"红树林- - 互花米草生态交错带"，在气候变化和人类活动双重影响下呈扩张趋势，成为监测和研究滨海湿地植被响应全球变化的重要区域。互花米草入侵红树林的格局、机制与后果，是中国红树林保护和恢复亟需解决的问题。.本项目采用野外竞争实验和水位梯度控制平台，从纬度、流域和潮间带尺度，研究红树植物和互花米草的种间相互作用对温度、盐度和潮位变化的响应，揭示生物和非生物因子交互作用下红树林- - 互花米草生态交错带的群落组织机制，预测交错带演替趋势；监测互花米草对不同发育阶段（繁殖体、幼苗、幼树）红树植物的影响，阐明互花米草影响下传播限制和生境限制在红树植物更新过程中的作用；对比分析中国和美国红树林- - 互花米草生态交错带的物种特性、种间相互作用和环境要素，探求引发中美交错带格局演变差异的主要驱动力。研究结果可为保护区域生态环境、应对全球变化提供科学依据。

互花米草于1979年从美国引入中国，经过近40年的扩散，已分布到沿海各省。互花米草在入侵地中国和原产地美国均与红树林形成“红树林——互花米草生态交错带”，在气候变化和人类活动双重影响下呈扩张趋势，是监测和研究滨海湿地植被响应全球变化的关键区域。互花米草入侵红树林的格局与机制，是中国红树林保护和恢复亟需解决的问题。.为全面了解互花米草的入侵特性，本项目沿大尺度纬度开展野外观测，分析了各地环境因子与植物生长的相关关系；通过同质种植园实验比较不同种源地互花米草的表型性状差异。研究发现：互花米草个体和种群水平的营养生长和繁殖性状随纬度变异显著。相比中高纬度，低纬度互花米草的生长和繁殖力低，扩散缓慢；除结实率这一有性繁殖特征外，其他表型性状的地理变异在同质种植园里消失了。这表明入侵中国的互花米草已呈现潜在的遗传分化；而互花米草的表型可塑性可能有利于其在入侵地的迅速扩张。.本项目从植物种间相互作用为切入点，采用竞争控制实验，探讨了沿纬度和潮位梯度的盐沼植物对红树植物的影响。在中国，互花米草均抑制红树植物幼苗的存活和生长；而在美国，盐沼植物对红树植物幼苗存活和生长为高纬度促进，低纬度抑制；红树植物在中潮位生长最好，而在高位和低位盐沼生长和存活较差。.我们进一步从“植物——动物”种间相互作用解释了红树林对互花米草入侵的响应机制。通过野外观测、控制实验和室内喂饲实验，揭示了蟹类对互花米草种子和实生苗的取食在互花米草早期建立过程中的关键作用，动物取食和植物竞争共同导致了红树林生境中互花米草更新失败。但在光滩，实生苗逃过动物取食而成功定居。互花米草通过大量传播种子和快速的无性克隆生长，已迅速侵占绝大部分的光滩、入侵到林窗，并包围健康完整的红树林。这一“草进林退”状况的持续发展，将可能导致红树林不可逆地转换为互花米草植被。我们需要采取早发现早治理的措施，以应对互花米草对高强度自然和人为活动影响下的中国红树林的威胁。