Increasing biodiversity generally enhances productivity through selection and complementarity effects not only in natural, but also in agricultural, systems. However, the quest to explain why diverse cropping systems are more productive than monocultures remains a central goal in agricultural science. In a mesocosm experiment, we constructed monocultures, two- and four-species mixtures from eight crop species with or without fertilizer and both in temperate Switzerland and dry, Mediterranean Spain. We measured physical factors and plant traits and related these in structural equation models to selection and complementarity effects to explain seed yield differences between monocultures and mixtures. Increased crop diversity increased seed yield in Switzerland. This positive biodiversity effect was driven to almost the same extent by selection and complementarity effects, which increased with plant height and specific leaf area (SLA), respectively. Also, ecological processes driving seed yield increases from monocultures to mixtures differed from those responsible for seed yield increases through the diversification of mixtures from two to four species. Whereas selection effects were mainly driven by one species, complementarity effects were linked to larger leaf area per unit leaf weight. Seed yield increases due to mixture diversification were driven only by complementarity effects and were not mediated through the measured traits, suggesting that ecological processes beyond those measured in this study were responsible for positive diversity effects on yield beyond two-species mixtures. By understanding the drivers of positive biodiversity–productivity relationships, we can improve our ability to predict species combinations that enhance ecosystem functioning and can promote sustainable agricultural production.

中文翻译：

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利用植物性状了解生物多样性效应对一年生作物群落生产力的贡献

增加生物多样性通常通过选择和互补效应提高生产力，不仅在自然系统中，而且在农业系统中。然而，解释为什么多样化的种植系统比单一种植更有生产力的探索仍然是农业科学的核心目标。在中宇宙实验中，我们在温带的瑞士和干燥的西班牙地中海地区，用八种有或没有肥料的作物种类构建了单一栽培、两种和四种混合物。我们测量了物理因素和植物性状，并在结构方程模型中将它们与选择和互补效应联系起来，以解释单一栽培和混合栽培之间的种子产量差异。作物多样性的增加提高了瑞士的种子产量。这种积极的生物多样性效应几乎是由选择和互补效应驱动的，它们分别随着株高和比叶面积（SLA）的增加而增加。此外，推动种子产量从单一种植到混合种植的生态过程不同于通过将混合物从两个物种多样化到四个物种而导致种子产量增加的生态过程。虽然选择效应主要由一个物种驱动，但互补效应与每单位叶重更大的叶面积有关。由于混合物多样化导致的种子产量增加仅由互补效应驱动，而不是通过测量的性状介导，这表明超出本研究中测量的生态过程对超过两种混合物的产量产生积极的多样性影响。