营养盐加富和鱼类添加对浮游植物群落演替和多样性的影响

浮游植物是水体生态系统敞水区最重要的初级生产者,其组成与多样性反映了群落的结构类型和存在状态。通过围隔实验,模拟水库春季发生的营养盐加富和鱼类放养的干扰,分析在这两种干扰下的浮游植物群落演替过程中优势种和稀有种的变化,并通过以丰度与生物量为变量的香农和辛普森多样性指数的计算,分析浮游植物群落演替过程中的多样性变化特征。结果表明,营养盐加富干扰下的浮游植物群落的优势种变化和演替更为明显,营养盐加富与鱼类添加对浮游植物群落多样性变化的影响符合中度干扰理论。在优势种优势度变化较大的浮游植物群落演替过程中,多样性指数与浮游植物生物量有较高的负相关性。在浮游植物群落演替过程中,香农和辛普森多样性指数的变化趋势基本一致,采用丰度与生物量为变量的两种多样性指数的计算结果对实验系统中浮游植物群落多样性的分析结果没有明显的影响。

Effects of nutrient enrichment and fish stocking on succession and diversity of phytoplankton community

Phytoplankton algae are the main primary producers in pelagic water, and their species diversity is a measure of the structure and state of communities.Phytoplankton is sensitive to external conditions such as nutrients, predators and hydrodynamics, because of its small size and high reproductive rate.In phytoplankton succession, both dominant species and rare species can markedly change with ecological factors, even over a short period.Species richness, Shannon's diversity and Simpson's diversity are widely used.However, these diversity indices are usually calculated by using abundance as the variable, while biomass is only rarely used.As abundance and biomass emphasize different aspects of community function, there may be a significant dissimilarity between the diversity calculated from these two variables.In the present study, an enclosure experiment system (nine enclosures, 4 m× 4 m and 6 m deep for each) was conducted, comprising three treatments (control, nutrient enrichment and fish stocking) in Liuxihe Reservoir, Guangdong.Each treatment had three replications.Nutrient enrichment and fish stocking were manipulated to simulate intermediate disturbance relative to the control (without fish stocking and nutrient enrichment).In the nutrient enrichment treatment, KH₂PO₄ was added to a targeted total phosphorus concentration of 0.018 mg/L, while fish was stocked to a fish density of 2 g/m³.Each enclosure was sampled every ten days from May 4 to July 26, 2012.We explored the changes in species composition by checking rare species, dominant species and diversity indices.Shannon's diversity and Simpson's diversity indices were calculated based on both abundance and biomass.The results showed that the phytoplankton community evolved most significantly in the nutrient enrichment treatment.Both nutrient enrichment and fish stocking treatments increased species diversity of the phytoplankton community, as predicted by the intermediate disturbance hypothesis.A significantly negative correlation between diversity indices and phytoplankton biomass only occurred when the dominance of dominant species became high.Shannon's diversity and Simpson's diversity indices displayed a similar pattern during the succession of the phytoplankton community.The diversity indices with the variables of abundance and biomass did not significantly differ in explaining the structure of the phytoplankton community.