云贵高原富营养化湖泊优势沉水植物维持机制的化学计量内稳性研究

Eutrophication has caused serious degradation of aquatic plants, especially submerged macrophytes, in Yangtze River floodplain lakes besides plateau lakes. Therefore, degradation and maintenance mechanisms of submerged macrophytes has been becoming an urgent task of lake restoration at present. Ecological stoichiometry is a useful concept with which to explore organisms' life forms and ecosystem structure and function in relation to the elemental ratios (stoichiometry) of environment (water, soil) and organisms. Stoichiometric homoeostasis is the ability of an organism to maintain a given elemental composition despite variation in the elemental composition of its environment or diet and re?ects the net outcome of many underlying physiological and biochemical adjustments as organisms respond to their surroundings. It is fundamental for establishment of ecological stoichiometry. Ecosystems are controlled by non-equilibrium flows of both materials (nutrients) and energy (carbon). Environmental stoichiometry can strongly affects an organism's stoichiometry, which may alter competitiveness of a species, leading to a shift of species composition. In the applying project, we want to explore whether/how environmental stoichiometry (eutrophication) change the stoichiometric homeostasis of submerged macrophytes in different eutrophic lakes of Yunnan-Guizhou plateau using the methods of comparative limnology and experimental limnology. The aim is to test the hypothesis that dominant submerged macrophyte has higher stoichiometric homeostasis with the increase of eutrophication. We also compare the differences in maintenance mechanism and restoration strategy of submerged macrophytes between plateau lakes and floodplain lakes. We hope restore aquatic plants in different eutrophic lakes according to stoichiometric homeostasis in order to gain biodiversity.

湖泊营养化进程导致水生植被尤其是沉水植被严重退化，高原湖泊也未能幸免，因此弄清营养化湖泊沉水植被的退化机理和优势沉水植物的维持机制，就成为我国富营养化湖泊沉水植被成功恢复的首要任务。基于此，本项目拟在前期沉水植被退化机理研究的基础上，围绕"化学计量内稳性高是富营养化湖泊现存优势沉水植物的维持机制"假设，以云贵高原湖泊和围隔生态系统为研究对象，将野外调查与控制实验相结合，运用生态化学计量学理论，阐释生态系统内C、N、P元素生态过程的改变(富营养化)对沉水植物的生活史、种群动态、群落结构的影响，明确不同营养水平下优势沉水植物的化学计量内稳性特征，揭示化学计量内稳性在富营养化湖泊优势沉水植物维持机制中的作用；并将高原与长江中下游富营养化湖泊中沉水植物的生态化学计量特征进行比较研究，探讨不同区域富营养化湖泊沉水植物的维持机制与恢复策略的异同。

基于生态化学计量学理论，我们选取了20个云贵高原富营养化湖泊作为对象，研究了富营养化湖泊现存优势沉水植物的维持机制。取得的主要结果如下：（1）典范对应分析结果表明，20个湖泊的营养水平可显著影响优势沉水植物组织的C, N, P等常量元素的含量和比例；而物种分类可显著影响Ca, K和Se等微量和有益元素的含量和比例。（2）微齿眼子菜、穗花狐尾藻、苦草和金鱼藻在不同N、P营养浓度胁迫下，他们的生长速率与组织N:P并没有一致的变化趋势，但是protein:RNA与生长速率的变化一致，均是负相关，表明protein:RNA与生长速率的关系可作为判定生物是否符合生长速率假说的可靠指标。另，苦草相比于其他三种水生植物，具有更高N:P内稳性，可能比其他三种更加耐高浓度氮磷营养胁迫。（3）无论是在云贵高原湖泊还是长江中下游平原湖泊，Co元素的化学计量内稳性均较高；长江平原湖泊还有较高的Cd元素化学计量内稳性，而云贵高原湖泊则有更高的Cr, Li和Pb的化学计量内稳性。典范对应分析的结果表明，两种湖泊类型的水体总氮 (WTN) 均显著影响沉水植物组织的As和Cd的含量和比例。典范判别分析的结果表明沉水植物物种组分显著影响两种类型湖泊沉水植物组织的元素含量和比例。（4）洪湖的研究结果表明，蓖齿眼子菜的N含量在两个湖区差异较大，然而沉水植物P含量在两个湖区间没有显著差异。与东部湖区相比，西半湖区有显著更高的C和C:P比。在全湖尺度上，沉水植物对沉积物N和N:P有显著影响。从2013年至2015年的调查数据表明，洪湖C含量逐渐降低，与透明度一致；但2017年C含量又上升，可能与2016年洪水冲刷有关。（5）云南高原湖泊有无沉水植物区域的沉积物和水体中金属含量没有显著差异。湖水和沉积物主要受金属As, Cr和Pb的污染。眼子菜对铁元素具有超级累作用。沉水植物组织的Cr元素与水体Cr具有显著的相关性。通过上述结果，希望能为高原湖泊的治理提供理论指导。