Species composition plays a key role in ecosystem functioning. Theoretical, experimental and field studies show positive effects of biodiversity on ecosystem processes. However, this link can differ between taxonomic and functional diversity components and also across trophic levels. These relationships have been hardly studied in planktonic communities of coastal upwelling systems. Using a 28-year time series of phytoplankton and zooplankton assemblages, we examined the effects of phytoplankton diversity on resource use efficiency (RUE, ratio of biomass to limiting resource) at the two trophic levels in the Galician upwelling system (NW Iberian peninsula). By fitting generalized least square models, we show that phytoplankton diversity was the best predictor for RUE across planktonic trophic levels. This link varied depending on the biodiversity component considered: while the effect of phytoplankton richness on RUE was positive for phytoplankton RUE and negative for zooplankton RUE, phytoplankton evenness effect was negative for phytoplankton RUE and positive for zooplankton RUE. Overall, taxonomic diversity had higher explanatory power than functional diversity, and variability in phytoplankton and zooplankton RUE decreased with increasing phytoplankton taxonomic diversity. Phytoplankton used resources more efficiently in warmer waters and at greater upwelling intensity, although these effects were not as strong as those for biodiversity. These results suggest that phytoplankton species numbers in highly dynamic upwelling systems are important for maintaining the planktonic biomass production leading us to hypothesize the relevance of complementarity effects. However, we further postulate that a selection effect may operate also because assemblages with low evenness were dominated by diatoms with specific functional traits increasing their ability to exploit resources more efficiently.

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浮游植物多样性对沿海上升流系统生态系统功能的影响

物种组成在生态系统功能中起着关键作用。理论、实验和实地研究表明生物多样性对生态系统过程产生积极影响。然而，这种联系在分类和功能多样性组成部分之间以及在营养级别之间可能有所不同。在沿海上升流系统的浮游群落中几乎没有研究这些关系。我们使用浮游植物和浮游动物组合的 28 年时间序列，研究了浮游植物多样性对加利西亚上升流系统（伊比利亚半岛西北部）两个营养级的资源利用效率（RUE，生物量与限制资源的比率）的影响。通过拟合广义最小二乘模型，我们表明浮游植物多样性是跨浮游营养水平的 RUE 的最佳预测因子。这种联系因所考虑的生物多样性成分而异：虽然浮游植物丰富度对 RUE 的影响对浮游植物 RUE 为正，对浮游动物 RUE 为负，但浮游植物均匀度对浮游植物 RUE 为负，对浮游动物 RUE 为正。总体而言，分类多样性比功能多样性具有更高的解释力，浮游植物和浮游动物 RUE 的变异性随着浮游植物分类多样性的增加而降低。浮游植物在较温暖的水域和更大的上升流强度中更有效地利用资源，尽管这些影响不如生物多样性那么强。这些结果表明，高动态上升流系统中的浮游植物物种数量对于维持浮游生物量生产很重要，这导致我们假设互补效应的相关性。然而，我们进一步假设选择效应也可能起作用，因为均匀度低的组合由具有特定功能特征的硅藻主导，从而提高了它们更有效地利用资源的能力。