洞庭湖典型群落交错带植被动态及群落维持机制

In recent years, the downward moving of vegetation zone indicates that the process of positive vegetation succession has been significantly accelerated in the Dongting Lake, and then leading to the comprehensive worries on the decline of lake's services and functions. Ecotone, as the transition zone between adjacent ecosystems, is the most sensitive area to the environmental change and also is the pioneer zone of the vegetation succession. Moreover, it is also the first step to understanding the succession rules of weltand vegetation correctly. In this project, the vegetation dynamic and community maintaining mechanism of the typical community ecotone in the Dongting Lake were studied. The contents of this project are as following: firstly,the characteristics of vegetation dynamic with the key influencing environmental factors were investigated by field investigation and indoor environmental factors analysis; secondly, the influencing mechanisms of the key environmental factors (e.g. flooding, sedimentation) on the vegetation dynamic were examined by periodic investigation in the fixed plots. Furthermore,the biological mechanism for the community maintaining was also investigated by varies competition experiments under different intensities of sedimentation or flooding. The objective of our study was to enrich the study content of community ecotone in the wetland system, and to provide theoretical rules for the protection of wetland resource and rehabilitation of degraded wetlands.

近几十年来，洞庭湖湿地植被正向演变趋势明显，表现为植被带整体下移，引发人们对湖泊湿地服务功能下降的担忧。群落交错带作为相邻生态系统的过渡带，具有生境异质性高、环境敏感性强等特点，是植被演变的先锋地带，也是正确认识湿地植被演替规律的基本前提。本项目拟以洞庭湖典型群落交错带为对象，通过野外调查及室内环境因子分析掌握交错带植被动态变化特征，揭示影响其动态的关键环境因子；通过野外模拟试验的定期监测，揭示关键环境因子（如水位高程、泥沙淤积）对交错带植被动态的影响及作用机理；通过不同水沙梯度下的竞争实验，揭示交错带群落维持的生物学机制。最后，综合各项研究成果，系统揭示洞庭湖典型群落交错带植被的动态变化及群落维持机制。本项目可充实和完善湿地群落交错带的研究内容，为水生植物资源保护、受损湿地的恢复提供依据。

近几十年来，洞庭湖湿地植被正向演变趋势明显，表现为植被带整体下移，引发人们对湖泊湿地服务功能下降的担忧。群落交错带作为相邻生态系统的过渡带，具有生境异质性高、环境敏感性强等特点，是植被演变的先锋地带，也是正确认识湿地植被演替规律的基本前提。本项目以洞庭湖典型群落交错带为对象，通过野外调查、室内环境因子分析及控制实验等方式对洞庭湖典型群落交错带植被动态及关键影响要素进行分析。研究结果表明：(1)洞庭湖荻-苔草群落交错带不同高程下植被特征、土壤特征差异明显。土壤含水量随高程增加逐渐降低，丰富度指数和多样性指数随高程增加呈先降低再增加的趋势。典型相关分析说明，土壤含水量与植物生物量及群落丰富度、多样性间具有很好的相关性；（2）典型群落交错带苔草生物量累积和分株数随淹水时间增加而减小，苔草可通过生物量分配和繁殖策略的调整来适应淹水环境。而南荻的生物量，高度均随时间增长而迅速积累，且低程区的总量和增长量均高于高程区；（3）干旱和水淹条件下，苔草 、辣寥和虉草三种植物的生长速率均受到抑制。丙二醛、质膜透性和脯氨酸分析结果表明，荻耐干旱的能力要强于其他两个物种，但耐水淹的能力明显弱于苔草和辣蓼；同时研究发现三种植物的淀粉和糖含量与其耐水淹及恢复能力存在一致性；(4)虉草、苔草和荻均具有明显的促淤效应，但促淤能力存在明显差异。具体表现为虉草>荻>苔草。同时，植被的存在明显改变了群落土壤的颗粒组成。多元线性回归分析表明，泥沙淤积特征与植被特征（如密度、高度、生物量）、淹水时间和群落分布高程具有明显的相关性；(5)不同密度+沙埋和不同密度+水位实验结果表明：较高的植物密度有助于植物抵抗干旱、泥沙淤积的胁迫，这主要通过植被改变生物量分配、淀粉及可溶性糖含量来实现的；(6) 不同沙埋强度下的竞争实验结果表明，沙埋条件下，邻体植株对苔草竞争强度逐渐减弱，苔草可通过间隔子伸长和游击性分株增加来适应竞争和淤积的环境。而不同水位条件下的竞争实验表明，不同水位条件下植被种间竞争强度随水位增加而明显减弱，辣廖可通过根系结构和生物量分配的调整来适应不同的水位和竞争环境。该项目对于系统揭示洞庭湖典型群落交错带植被的动态变化及群落维持机制以及水生植物资源保护、受损湿地的恢复具有重要意义。