Data from: Different response-effect trait relationships underlie contrasting responses to two chemical stressors

1. Trait-based approaches predict ecosystem functioning under environmental change by relating traits predicting changes in species densities (response traits) to traits driving ecosystem functioning (effect traits). Stressors can however affect ecosystem functioning not only by altering species densities, but also by directly changing species effect traits. 2. We first identified the response traits predicting the cell density of 18 marine benthic diatom strains along gradients of two chemical stressors (a pesticide and a metal, atrazine and copper). We then tested if response traits could predict stressor-induced changes in ecosystem functioning, i.e. changes in the effect traits driving the diatoms’ potential contribution to primary production, sediment stabilization and energy content in intertidal systems. Finally, we examined if changes in density and changes in ecosystem functioning were correlated, to assess whether species capable of growing under stressful conditions could maintain their contribution to ecosystem functioning. 3. The relationship between response traits and stressor-induced changes in density and ecosystem functioning was different depending on stressor type: a set of intercorrelated morphological traits predicted changes in both density and ecosystem functioning under metal stress, with large cells being more stress-resistant. Changes in density and changes in ecosystem functioning were positively related: diatoms whose density was least affected by the metal were also able to sustain functioning under metal exposure. 4. In contrast, the capacity for mixotrophic growth predicted changes in density, but not changes in ecosystem functioning under pesticide stress. Pesticide effects on density and on ecosystem functioning were negatively related for energy content and sediment stabilization, indicating a limited capacity of pesticide-tolerant diatoms to maintain their contribution to ecosystem functioning. Synthesis. Ecosystem functioning under stress can depend on whether response traits driving changes in density also predict direct stress effects on the species’ contribution to ecosystem functioning. Based on our results, we expect a disproportionate loss of functioning when traits driving species densities do not allow to maintain ecosystem functioning under stress.1. 基于性状的研究方法（Trait-based approaches）通过将预测物种密度变化的性状（响应性状，response traits）与驱动生态系统功能的性状（效应性状，effect traits）相关联，来预测环境变化下的生态系统功能。然而，胁迫因子不仅可以通过改变物种密度来影响生态系统功能，还可以直接改变物种的效应性状。 2. 本研究首先鉴定了在两种化学胁迫因子——除草剂莠去津（atrazine）与金属铜（copper）——的浓度梯度下，18株海洋底栖硅藻（marine benthic diatom）的细胞密度预测响应性状。随后，我们检验响应性状能否预测胁迫因子诱导的生态系统功能变化，即驱动硅藻对潮间带系统初级生产、沉积物固持以及能量含量潜在贡献的效应性状的变化。最后，我们探究了密度变化与生态系统功能变化之间的相关性，以评估在胁迫条件下能够生长的物种能否维持其对生态系统功能的贡献。 3. 响应性状与胁迫因子诱导的密度及生态系统功能变化之间的关系因胁迫类型而异：在金属胁迫下，一组相互关联的形态性状可同时预测密度与生态系统功能的变化，且大型细胞具有更强的胁迫耐受性。密度变化与生态系统功能变化呈正相关：受金属胁迫影响最小的硅藻，在金属暴露环境中也能够维持其生态系统功能。 4. 与之相反，混合营养生长（mixotrophic growth）能力可预测密度变化，但无法预测除草剂胁迫下的生态系统功能变化。除草剂对密度与生态系统功能的影响在能量含量与沉积物固持两项指标上呈负相关，这表明耐受除草剂的硅藻维持其生态系统功能贡献的能力有限。 Synthesis. 胁迫条件下的生态系统功能，取决于驱动物种密度变化的响应性状是否也能预测胁迫对物种生态系统功能贡献的直接影响。基于本研究结果，我们推测，当驱动物种密度的性状无法在胁迫条件下维持生态系统功能时，将出现不成比例的功能损失。