Data from: Beyond shading: litter production by neighbours contributes to overyielding in tropical trees

The influence of biodiversity on ecosystem functioning is now well established. However, our ability to predict the ecological consequences of biodiversity changes remains limited by our poor understanding of the mechanisms underlying biodiversity effects. We disentangled the contributions of light competition and residual neighbourhood interactions in a ten-year-old biodiversity experiment with tropical trees that display overyielding, i.e., higher community-level yields in mixtures compared with monocultures. We developed models of individual tree growth that partition the effects of neighbouring trees into shading and residual effects assumed to reflect primarily belowground interactions. These models reject the hypothesis that reduced light competition in mixtures is the only mechanism driving overyielding. After factoring out the effects of shading, litter production by neighbours was a far better predictor of tree growth than traditional crowding indices and contributed to overyielding by producing pairwise interactions that ranged from competitive to facilitative, but which on average concentrated competition within species. Consistent with litter-mediated biodiversity effects, the magnitude of overyielding increased over time. Our results provide evidence for diversity effects extending beyond that of light and reveal the neglected role of litter-mediated interactions among trees.

生物多样性（biodiversity）对生态系统功能（ecosystem functioning）的影响现已得到学界广泛证实。然而，由于对生物多样性效应背后的内在机制认知不足，我们预测生物多样性变化所引发的生态后果（ecological consequences）的能力仍十分有限。我们在一项为期十年的热带树木生物多样性实验中，解析了光竞争（light competition）与剩余邻体相互作用（residual neighbourhood interactions）的贡献——该实验中的热带树木呈现超产效应（overyielding），即混播群落的群落水平产量高于单作（monocultures）群落。我们构建了单木生长（individual tree growth）模型，将邻树的影响划分为遮阴效应（shading）与剩余效应，其中剩余效应主要被认为反映了地下相互作用（belowground interactions）。这些模型驳斥了"混播群落中光竞争的减弱是驱动超产效应的唯一机制"这一假说。在扣除遮阴效应的影响后，邻体的凋落物产量（litter production）相较于传统拥挤指数（crowding indices），是更优的单木生长预测因子，其通过产生从竞争到促进（facilitative）的两两相互作用（pairwise interactions）促进了超产效应，但这类相互作用在平均水平上将竞争集中于种内范围。与凋落物介导的生物多样性效应相一致，超产效应的强度随时间推移不断增强。我们的研究结果证实，生物多样性效应不止局限于光竞争层面，并揭示了树木间凋落物介导的相互作用这一长期被忽视的重要角色。