Data from: Allelopathy prevents competitive exclusion and promotes phytoplankton biodiversity

It has been hypothesized that allelopathy can prevent competitive exclusion and promote phytoplankton diversity in aquatic ecosystems, where numerous species coexist on a limited number of resources. However, no experimental proof-of-principle is available to support this hypothesis. Here we present the first experimental evidence supporting this hypothesis by demonstrating that allelopathy promotes the coexistence of two phytoplankton species (Ankistrodesmus falcatus and Oscillatoria sp.) competing on a single limiting nutrient. By performing long-term competition experiments in nitrate-limited continuous cultures, and describing the population dynamics using a mechanistic model, we demonstrate that when allelopathy comes into play, one of the following outcomes is possible depending on the relative initial abundances of the species: dominance of the stronger competitor for nitrate (the non-allelopathic species), oscillatory coexistence, or dominance of the weaker competitor (the allelopathic species). Our model analysis reveals that sustained oscillatory coexistence of the two-species coexistence would be a common outcome of this experiment. Our study confirms for the first time, based on laboratory experiments combined with mechanistic models, that allelopathy can alter the predicted outcome of inter-specific competition in a nutrient-limited environment and increase the potential of coexistence of more species than resources, thereby contributing to find endogenous mechanisms explaining the extreme diversity of phytoplankton communities.

已有假说提出，化感作用（allelopathy）可在水生生态系统中阻止竞争排除，促进浮游植物（phytoplankton）多样性——此类生态系统中众多物种依托有限的资源共存。然而，目前尚无支撑该假说的原理性实验证据。本研究首次提供了支持该假说的实验证据，证明化感作用可促进两种浮游植物物种：镰形纤维藻（Ankistrodesmus falcatus）与颤藻属（Oscillatoria sp.）在单一限制性养分条件下的共存。我们通过在硝酸盐限制的连续培养体系中开展长期竞争实验，并借助机理模型描述种群动态，证实：当化感作用发挥作用时，根据物种的初始相对丰度，实验将出现以下三种结果之一：对硝酸盐竞争力更强的非化感物种占据优势、振荡式共存，或是竞争力较弱的化感物种占据优势。模型分析显示，双物种的持续振荡共存将是本实验的常见结果。本研究首次结合实验室实验与机理模型证实，化感作用可改变养分限制环境下种间竞争的预测结果，提升物种数多于资源数的共存可能性，从而为解释浮游植物群落极端多样的内在机制提供了新的依据。