Distribution of aquatic macrophytes along depth gradients in Lajeado Reservoir, Tocantins River, Brazil

Abstract Aim The present study investigated the diversity of aquatic macrophytes in the littoral zone of Lajeado Reservoir, Tocantins River. We characterized spatial variations in species richness, composition and abundance along depth gradients. Methods Macrophyte sampling occurred at the end of the dry season (September and October 2014) in four sites of the reservoir. We established transects perpendicular to the shoreline, each 25 m long, divided in 3 sections (plots of 5 x 5 m). Results In total, we recorded 18 taxa of aquatic macrophytes, belonging to nine families and four life forms. Najas microcarpa, Echinodorus tenellus. and Chara sp. were the more frequent and abundant taxa. Considering depth gradients, we recorded 18 taxa in the section closer to the shoreline, 13 in the middle section and 10 in the section more distant to the shoreline. Submerged and emergent species were more frequent and abundant, especially in the section close to the shoreline; epiphytes and free-floating species were rare. Plot species richness (total, emergent and submerged) decreased along the gradient, and a Non-Metric Multidimensional Scaling (NMDS) revealed that the plot close to the shoreline had different composition when compared to adjacent sections. Individual species showed particular behaviors, but most tended to decline in abundance and occurrence along the gradient. Conclusions The present study revealed that small-scale environmental gradients affect the distribution of aquatic plants in Lajeado Reservoir, with greater diversity in habitats close to the shoreline.

摘要：本研究旨在调查托坎廷斯河拉热亚多水库沿岸带的水生大型植物（aquatic macrophytes）多样性，并解析沿深度梯度的物种丰富度、组成及丰度的空间变异特征。方法：于2014年旱季末期（2014年9月、10月）在该水库的4个采样点开展水生大型植物采样工作。研究设置了垂直于湖岸的样带，每条样带长25 m，划分为3个5 m×5 m的样方。结果：本次调查共记录到水生大型植物18个分类单元，隶属于9个科，涵盖4种生活型。其中，小果茨藻（Najas microcarpa）、细叶皇冠草（Echinodorus tenellus）及轮藻属（Chara sp.）为出现频率与丰度最高的类群。沿深度梯度分析显示，近岸区段共记录18个分类单元，中部区段13个，远岸区段仅10个。沉水植物与挺水植物的出现频率及丰度更高，尤其集中在近岸区段；附生植物与自由漂浮植物则较为罕见。样方的物种丰富度（总物种数、挺水植物及沉水植物）沿深度梯度呈下降趋势；非度量多维尺度分析（Non-Metric Multidimensional Scaling，NMDS）结果显示，近岸样方的物种组成与相邻区段存在显著差异。多数物种的丰度与出现频率沿该梯度呈下降趋势，仅少数类群表现出独特的分布格局。结论：本研究证实，小型尺度的环境梯度会影响拉热亚多水库内水生植物的分布格局，近岸生境的物种多样性更高。