丹江口水库真核浮游植物群落分布特征及其与环境因子的关系

浮游植物是湖库生态系统物质循环和能量流动的主要参与者，了解其群落组成对保护水生生态系统平衡具有重要意义.2021年6月在南水北调中线工程水源地丹江口水库淅川库区设置7个采样点，分4层分别在0.5、5、10和20 m处共采取28个样品.采用高通量测序测定真核浮游植物群落结构，分析真核浮游植物群落在水平和垂向上的分布特征.采用冗余分析探讨了浮游植物主要类群与环境因子的关系.结果表明：①库区真核浮游植物共12门68属，物种为甲藻-硅藻-绿藻型结构.水平方向上浮游植物群落差异较大，各采样点垂直方向上浮游植物丰度和多样性存在较大差异.宋岗、土门和党子口浮游植物群落多样性和丰度随水深增加呈下降趋势，其他采样点的浮游植物群落与水深关系趋势不明显.②硝氮（NO₃^--N）、水深、溶解氧（DO）、pH和水温（WT）是影响库区浮游植物垂直分布的重要环境因子.环境因子对浮游植物门类影响各异，甲藻门与NO₃^--N和水深呈负相关，与其他环境因子呈正相关；硅藻门与NO₃^--N和水深呈正相关，与其他环境因子呈负相关；绿藻门与WT、pH和DO呈负相关，与水深无明显相关性.

Characteristics of Eukaryotic Phytoplankton Community Structure and Its Relationship with Environmental Factors in Danjiangkou Reservoir

Eukaryotic phytoplankton play crucial roles in ecosystem processes, and understanding their community composition and abundance is of great importance to protect the balance of aquatic ecosystems. Danjiangkou Reservoir is a canyon lake in central China that acts as the water source of the Mid-route of South-to-North Water Diversion Project. In this study, the composition of planktonic microeukaryotes from water samples with a depth ranging from 0.5 to 20 m in Danjiangkou Reservoir were investigated using high-throughput 18S rDNA gene sequencing. The environmental factors including pH, water temperature (WT), nitrate (NO₃^--N), ammonia (NH₄⁺-N), total nitrogen (TN), conductivity (Cond.), water depth, and dissolved oxygen (DO) in the reservoir areas were measured, and their correlations with the abundance and diversity of eukaryotic phytoplankton were analyzed. The results of high-throughput sequencing showed that a total of 68 genera of phytoplankton belonging to 12 phyla were detected, and the phytoplankton communities were mainly composed of Dinophyceae, Bacillariophyta, and Chlorophyta. In particular, significant differences in the diversity of phytoplankton communities on a vertical distribution were found. The diversity and abundance of the phytoplankton communities in Songgang (SG), Tumen (TM), and Dangzikou (DZK) decreased with the increase in water depth, and the relationship between phytoplankton and water depth in other sampling sites was not obvious. The results of RDA showed that NO₃^--N, water depth, DO, pH, and WT could influence the vertical distribution of the phytoplankton community in the Danjiangkou Reservoir. Among these phytoplankton types, Dinophyceae was negatively correlated with NO₃^--N and water depth and positively correlated with other environmental factors. Meanwhile, Bacillariophyta was positively correlated with NO₃^--N and water depth and negatively correlated with other environmental factors. In addition, Chlorophyta was negatively correlated with WT, pH, and DO and not significantly correlated with water depth.