桂林寨底地下河沉水植物群落结构调查及影响因子分析

为研究岩溶地下河沉水植物分布、群落组成及生境对群落结构的影响,2013年7-8月,对寨底地下河沉水植物分布及群落多样性进行了调查,并结合全年水质监测数据,分析了生境对沉水植物群落多样性分布的影响。结果表明,寨底地下河出口共有沉水植物4科、6属、8种;优势种为苦草(Vallisneria natans)、靖西海菜花(Ottelia acuminata var.jingxiensis)、竹叶眼子菜(Potamogeton wrightii)和黑藻(Hydrilla verticillata),优势度分别为33.87%、23.10%、19.06%和12.50%,其中苦草为第一优势种。河道基质是制约沉水植物多样性分布的重要因素,砂石基质处沉水植物为种类单一的海菜花群落;泥沙混合处沉水物种组成比较丰富,海菜花、黑藻、竹叶眼子菜、苦草等形成共优势群落。岩溶水高Ca2+和HCO-3环境为沉水植物光合作用提供了丰富的矿物质元素及光合作用碳源。研究结果可为寨底地下河岩溶水生生态系统中沉水植物碳汇效应提供理论支持。

Effect of Karst Geology on the Submerged Macrophyte Community in Zhaidi River, Guilin

The karst carbon sink has been receiving increasing attention in studies of the global carbon cycle. Karst water is characterized by high concentrations of Ca2+ and HCO3-. Karst water accelerates growth of algae and produces a net carbon sink. Submerged macrophytes with relatively high biomass are an important component of karst aquatic ecosystems and some utilize HCO3- as the inorganic carbon source for photosynthesis. To analyze the impact of karst water on the community structure of submerged macrophytes, the distribution and community composition of submerged macrophytes were investigated in Zhaidi River, a typical subterranean karst river in Guilin, Guangxi Province. Our investigation was conducted in the surface section of the river, 3-9 m in width and approximately 512m in length. In July and August of 2013, samples of submerged macrophytes were collected from sample plots (1 m×1 m) at six sites. All plants were rinsed thoroughly and classified by species. The wet weight and average biomass of each species were measured and the frequency of occurrence and area were recorded. A WTW350i multifunction water quality analyzer was used to measure pH and water depth and transparency were measured using a Secchi disc. During 2013, water samples were collected monthly from where the Zhaidi River surfaced. Total dissolved solids (TDS), Ca2+ and HCO3- concentrations were measured at the Institute of Karst Geology, Chinese Academy of Geological Science (CAGS), and free CO2 were determined by titration with standard NaOH. Eight species of submerged macrophyte were collected, belonging to four families and six genera. The dominant species were Vallisneria natans, Ottelia acuminata var. jingxiensis, Potamogeton wrightii and Hydrilla verticillata, accounting, respectively, for 33.87%, 23.10%, 19.06% and 12.50% of the total macrophytes collected. Channel composition of the Zhaidi River was a key factor in controlling the distribution of the submerged macrophyte community. A sandstone channel supported a single species (Ottelia acuminata var. jingxiensis) while a mud and sandstone channel supported a high level of macrophyte diversity and Ottelia acuminata var. jingxiensis, Hydrilla verticillata, Potamogeton wrightii and Vallisneria spiralis formed a symbiotic community. Analysis of water quality parameters indicates that the high concentrations of Ca2+ and HCO3- found in karst water was beneficial for the growth of the submerged macrophytes in Zhaidi River. The study supplies a theoretical basis for further study of submerged macrophyte and the carbon sink effect associated with karst aquatic ecosystems.