珠三角河网裸藻的多样性特征

Biodiversity pattern of euglenophyta in the river network of the Pearl River Delta,China

珠三角河网是珠江汇入南海的必经之地,2012年对该水域裸藻门及各属的多样性特征及影响因子进行系统阐析。调查期间共发现裸藻12属84种,其中裸藻属是最主要类群,其次为扁裸藻属和囊裸藻属。珠三角河网独特的地理位置和人类活动造成的水体富营养化是该水域裸藻物种多样性丰富的主要原因。季节特征显示,丰水期裸藻的种类丰富度和生物量均明显高于枯水期。除了洪水引发的裸藻物种的外源供给增大外,泄洪所带来的有机质的增加也是有利因素。此外,丰水期对应的高温也是有益条件。空间特征存在明显的季节差异,丰水期河网外侧站位的生物量和种类丰富度高于中部站位,主要原因是受径流影响较大;枯水季节除广州附近站位的值明显偏高外,其它站位间差异不大,营养盐的空间格局是主要决定因素。尽管裸藻主要依赖于沿江静水水体中的外源供给,分析表明,其在随水流下行的过程中存在增长过程。不同藻属相对组成的结果显示,扁裸藻属和囊裸藻属因属于生长缓慢的K-选择策略型,富集营养物质的能力不及裸藻属,仅在枯水期与裸藻属形成互补优势。裸藻门及主要属的生物量与种类丰富度呈线性正相关关系,偏重于多样性单峰模式的上升区。

The Pearl River Delta （PRD） in Guangdong province is one of the most prosperous areas of China. At the same time, a large increase in the production of domestic and industrial waste occurred because of this economic development, and a 10% increase in waste production is estimated to have occurred in the past few years. The complicated river delta system, characterized as criss-cross and multiple river channels, is the primary location at which the Pearl River reaches the South China Sea. Many studies have focused on physical and chemical factors functioning in this region, especially in recent years, but few have investigated their effects on aquatic organisms. To understand the temporal and spatial distribution patterns of Euglenophyta, a riverine phytoplankton community, seasonal investigations were carried out in the river delta area in 2012. Thirteen representative sampling sites settled cover almost the whole river delta area. The correlation between the species richness and the biomass of each genus, and environmental factors is also analyzed in order to identify the key components of the interaction mechanism, using the PCA method. Moreover, the regional characteristics of the phytoplankton biodiversity pattern were evaluated at the genus level, using these results. During the investigation, 84 taxonomic species （including variant and derivative） from 12 genera of Euglenophyta were identified. The high biodiversity in this area is the result of its characteristic geographic features and high rate of eutrophication due to human activities. Of all the genera of Euglenophyta, Euglena contributed most to species richness and biomass, followed by Phacus and Trachelomonas. Although euglenoids in rivers are mainly dependent on exterior supplements from the influx of lentic waters into the river ecosystems, the present results revealed that euglenoids could grow along the river flows. Seasonal variation patterns of species richness and biomass were high in wet seasons and low in dry seasons. Besides the exterior supplementation by water flows during flood periods, simultaneous augmentation of organisms by flows could also promote the growth of euglenoids. Moreover, the corresponding high temperatures present during flood periods also benefit the growth of euglenoids. The spatial distribution pattern of euglenoids showed apparent seasonal differences. During flood periods, the values of the outer sites were significantly higher than those of inner sites, a dynamic mainly associated with variations in flow conditions. In drought periods, the differences among the rural sites were not so significant, but the extremely high values in urban sites were the result of high nutrient influx. The contribution of different genera indicated that Phacus and Trachelomonas could only co-dominate with Euglena during drought periods, and exhibited the K-selection strategy, which is generally characterized by a slower nutrient gathering capacity. In addition, the relationship between the biomass and species richness of euglenoids was analyzed, and it had an incline to the ascending curve part of the unimodal function of global phytoplankton biodiversity patterns.