Phytoplankton in the Mitika Wetland, Tibet, China: 1. Spatio-temporal niche of dominant species

Abstract

为了解青藏高原湿地浮游植物在时空不同维度上的分布特征，本文选取西藏四大国际湿地之一的麦地卡湿地作为研究地点，于2019年7月和10月在麦地卡湿地主要水系——麦地藏布及其支流和湖泊，设置了14个样点，采集了2个水情期（丰水期和枯水期）浮游植物的水样共252个.通过活体观察和固定染色方法鉴定浮游藻类物种，使用直接计数法统计浮游藻类的数量.计算麦地卡湿地浮游植物优势种的优势度指数（Y）、更替率（r）、生态位宽度（B_i）、生态位重叠值（O_ik）和生态响应速率（R），运用生态位分化的方法，对麦地卡湿地浮游植物优势种的生态位进行了不同时空维度的研究.结果表明：本研究中鉴定出浮游植物优势种（Y>0.02）共8种，其中克洛脆杆藻（Fragilaria crotomensis）和窗格平板藻（Tabellaria fenestrata）是2个水情期的共有优势种.生态位宽度值差异较大，可分为三大生态位类群，且优势度指数与生态位宽度值呈极显著正相关.总体上浮游植物优势物种的生态位重叠值高，在时间、空间和时空三个维度上O_ik>0.6的分别占89.29%、60.71%和28.57%.生态响应速率之和在时间维度上为负数，在空间和时空维度上为正数，说明该湿地浮游植物群落处于发展阶段.冗余分析表明，酸碱度、溶解氧、总氮和浊度是影响麦地卡湿地浮游植物优势种分布的重要因素，浮游植物优势种在这些环境因子上存在明显的生态分化现象.;In order to understand the distribution characteristics of phytoplankton at the spatial and temporal dimensions in wetlands in Qinghai-Tibet Plateau, Mitika Wetland, one of the four international wetlands in Tibet, was selected as the research area where 14 sampling points were set up along the main water system-Miti Tsangpo and its tributaries, and lakes in July and October 2019. A total of 252 water samples of phytoplankton were collected in two hydrological periods (wet season and dry season). The species of phytoplankton were identified by living observation and fixed staining method and counted by direct counting method. The dominance index (Y), replacement rate (r), niche width (B_i), niche overlap value (O_ik) and ecological response rate (R) of the dominant phytoplankton species were calculated. The niche differentiation method was used to analyze the niche of dominant species of phytoplankton at different dimensions in time and space. According to the dominance index, 8 dominant species (Y>0.02) of phytoplankton were identified among which Fragilaria crotomensis and Tabellaria fenestrata were the common dominant species in two periods, The niche width values of dominant species were quite different and can be divided into three niche groups, and the dominance index was positively correlated with the niche width. The niche overlap values of phytoplankton dominant species were high at the spatial, temporal and spatial-temporal dimensions with O_ik>0.6 accounting for 89.29%, 60.71% and 28.57%, respectively. The sum of ecological response rates was negative at the temporal dimension and was positive at the spatial and the spatial-temporal dimension indicating that the phytoplankton community was at developing stage in the wetland. RDA analysis showed that, pH, DO, total nitrogen and turbidity were the important factors affecting the distribution of dominant phytoplankton species in the Mitika Wetland, and there was obvious ecological differentiation in the dominant species of phytoplankton at these environmental factors.