基于生态化学计量学的洞庭湖湿地植被演替规律及水文驱动机制

In recent years, the process of vegetation succession in the Dongting Lake has been significantly accelerated due to the global change and high-intensity of human disturbance, and which results in significant worrying about the degraded functions of this lake. The law of vegetation succession can be reflected well by studying on the ecological stoichiometric characteristics of different successional stage vegetation. However, studies on the relationship of vegetation succession and ecological stoichiometry are scares espeically in the wetland ecosystem. In this project, the ecological stoichiometry explanation for the vegetation succession with its hydrological driving mechanism in the Dongting Lake Wetland was studied. The contents of this project are as following: firstly, the ecological stoichiometric pattern and stoichiometric homeostasis characteristics of vegetation with different successional stage, as well as its key influencing environmental factors were investigated by fixed - plot investigation and environmental factors analysis; secondly, the influences within mechanisms of the water level elevation on the dynamics and variance of ecological stoichiometry of typical vegetation were examined by the fixed - plot investigation and environmental factors analysis. Furthermore, the adjusting mechanisms of typical water regimes (water level, inundation cycle) on the ecological stoichiometry of typical wetland vegetation were investigated by varies of simulating experiments. The objective of our study was to improve our understanding on the rule of vegetation succession and the relationship between vegetation succession and ecological stoichiometry, and to provide theoretical basics for the protection and utilization of wetland vegetation resource.

近年来受全球变化及人类重大工程的影响，洞庭湖湿地植被带整体下移，正向演替趋势明显，引发了人们对湖泊湿地生态服务功能下降的担忧。不同演替阶段植被生态化学计量学的研究可以很好的反映植被演替规律。但当前湿地生态系统中，有关二者相关性的研究相对较少。本项目拟以洞庭湖不同演替阶段湿地植被为对象，通过不同时期固定样地调查及环境因子分析，揭示不同演替阶段植被化学计量格局、生态化学计量内稳性特征及关键影响因子；通过不同高程典型植被群落调查及环境因子分析，揭示典型植被化学计量特征在不同水位高程下的动态及变异规律；通过典型水文情势（水位、淹水周期）下的控制实验，阐明典型水文情势调控湿地植被演替的生态化学计量学机制。最后整合各项研究成果，系统分析植被生态化学计量特征与湿地植被演替的相关性，深入揭示湿地植被演替规律及其生态化学计量学机制，为洞庭湖植被演替规律的预测、湿地保护与利用提供科学依据。

本项目主要以洞庭湖湿地为研究对象，通过野外大范围调查、野外固定样地监测及模拟控制实验等手段，系统研究洞庭湖不同演替阶段湿地植被、土壤生态化学计量特征，阐明海拔、不同水文情势及养分添加等条件下湿地植被生态化学计量特征的变化规律及作用机制，主要结论如下：（1）短尖薹草群落土壤总碳、碱解氮含量、C:P和N:P明显高于藜蒿和荻群落，C:N最高值为荻群落；虉草和南荻叶片的总氮、总磷平均含量高于苔草，叶片N:P值随海拔增加逐渐减少，土壤含水量是影响植被生长及生态化学计量特征的关键因子；（2）不同高程植被的土壤SOC、TN、C:N、C:P 和N:P均随高程增加而增加，SOC、TN、C:P和N:P的空间分布相似，C:N空间分布均一；（3）短尖薹草株高、密度、盖度、地上生物量和土壤有机质、全氮、全磷含量均随高程增加先增加后减少，短尖薹草叶片总碳含量与C:N、C:P、N:P比值随高程增加而增加，而总氮、总磷含量则相反，海拔高程可通过影响淹水时间、土壤水分含量等影响植被生长及化学计量特征。随着时间的推移，低海拔下短尖薹草叶片总碳含量逐渐减少，而中高海拔叶片总碳含量则先增加后减少，叶片总氮和总磷含量、C:N和C:P则相反；（4）苔草地上生物量、密度和株高、总碳、C:N和C:P比值均随着水位的增加而降低，而总氮、总磷含量则相反；淹没和恢复条件下短尖苔草的生物量、密度、C:N和C:P比值均随着淹水时间的增加而降低，而总氮、总磷含量则相反；（5）不同基质和水位交互作用下，短尖苔草和辣蓼地上部分符合生长速率假说而地下部分不符合；（6）不同养分添加实验表明短尖苔草生物量累积、生物量分配、总氮含量均以添加0.2 g kg-1磷肥处理最高，叶片和根磷含量随着磷浓度增加而显著增加，而C:P和N:P则相反；短尖薹草生物量累积在两次添加下最高，叶氮含量在一次添加下最低，叶和根的C:N在对照组最低，而C:P和N:P则相反，表明不同频次磷添加对短尖薹草不同器官生物量分配及化学计量特征具有明显影响。