沉水植物繁殖生物学特性对人为水位节律的适应

Over evolutionary time, submerged plants have evolved traits that enable them to adapt to natural water level fluctuations. However, with the increasing use of water resources by human, seasonal water level fluctuation of rivers and their connected lakes are changing intensely. How do submerged plants, which have adapted to natural water regimes, respond to the environmental change to maintain and expand their populations and to function in river and lake wetlands? This project will select several widespread submerged species as materials, comparing with their closely-related non-widespread and exotic spcies. Extensive field investigations will be carried out in rivers and lakes in the middle and lower reaches of the Yangtze River to record the environmental factors such as water level, temperature and sunlight at the life stages of propagule production, dormancy and germination. Based on the environmental data abtained from field investigations, many combinations of gradients of water level fluctuation and other environmental factors will be designed in indoor experiments to analyze the relationships among environmental factors, which affect the life activities of propagules in an interactive way. Through the relationships among the factors, the determinative factor in each stage will be disclosed. Simultaneously, in ourdoor experiments, water level fluctuations simulating the water regulation of dams and sluices, combined with other environmental factors, will be designed to study the responses of propagules to seasonal water level fluctuation modified by human activities in different life stages. The results from this project will provide scientific basis for predicting the potential population development of submerged species subjected to seasonal water level fluctuations modified by human activities and for establishing management measures of sustainable development of wetland ecosystems.

在长期的进化过程中，沉水植物已经适应了自然的水位季节节律。然而，随着人类对水资源利用的日益增加，河流及与其相通的湖泊的水位节律发生了巨大改变。在进化过程中已经适应自然水位节律的沉水植物会怎样适应剧变的环境而获得种群的维持和发展，发挥它们在河流和湖泊湿地生态系统中的作用？本项目拟以几个沉水植物广布种为主要研究材料，并与它们近缘的非广布种和外来种相比较，在长江中下游地区的河流和湖泊中进行广泛的野外考察和样品采集，记录繁殖体形成、休眠和萌发期间的水位、温度、光照等环境条件；然后设计室内实验，研究各生活史阶段环境因子在影响繁殖体生命活动中的相互关系，辨别各阶段的主导因子；并在室外模拟大坝和涵闸对水位的控制，研究水位节律与其它环境因子关联性发生改变后沉水植物繁殖体的生命活动。本项目的研究成果有望增进我们理解人为水文情势下沉水植物的种群发展动态，为制订河流和湖泊湿地生态系统的有效管理措施提供依据。

为了利用水资源，人类建造的河流大坝和江湖涵闸使河流及与其相通的湖泊的水位节律发生了巨大改变。河流大坝上游水位节律一般为冬春高水位、夏季低水位，常与冬春低水位、夏季高水位的自然节律相反。江湖涵闸使阻隔湖泊水位的波动减少，趋于稳定。沉水植物是河流和湖泊生态系统的重要组成成分，它们在长期的进化过程中已经适应了自然的水位季节节律，而面对人为干扰的水位节律沉水植物会做出相应的调整。本项目通过模拟河流大坝和江湖涵闸控制下的人为水位节律，并与模拟的自然水位节律比较，研究了人为干扰的水位节律对沉水植物生命活动的影响，发现水位节律变化对沉水植物的影响因物种而异。有些物种的生长受到人为水位节律的促进，如在模拟河流大坝上游水位中苦草生长得更旺盛并具有更强的营养繁殖能力，模拟江湖涵闸引起的稳定水位有利于伊乐藻的春季生长并可能提高穗花狐尾藻在春季群落中的地位；有些物种的生长却受到人为水位节律的抑制，如模拟江湖涵闸引起的稳定水位抑制菹草的生长；有些物种受人为水位节律的影响因季节而异，如模拟河流大坝上游水位节律抑制了金鱼藻夏季的生长，而其冬季生长却没有受到显著影响。本项目的研究结果表明：在湿地生态系统的管理、保护和恢复过程中，河流大坝和江湖涵闸引起的人为水位节律变化是一个不容忽视的重要因素。水位节律变化可能引起沉水植物营养生长和繁殖活动的变化，这种变化因物种而异，从而可能引起沉水植物群落结构的变化以及与之相关的生态功能的变化。