The effects of biodiversity on ecological processes have been experimentally evaluated mainly at the local scale under homogeneous conditions. To scale up experimentally based biodiversity‐functioning relationships, there is an urgent need to understand how such relationships are affected by the environmental heterogeneity that characterizes larger spatial scales. Here, we tested the effects of an 800‐m elevation gradient (a large‐scale environmental factor) and forest habitat (a fine‐scale factor) on litter diversity–decomposition relationships. To better understand local and landscape scale mechanisms, we partitioned net biodiversity effects into complementarity, selection, and insurance effects as applicable at each scale. We assembled different litter mixtures in aquatic microcosms that simulated natural tree holes, replicating mixtures across blocks nested within forest habitats (edge, interior) and elevations (low, mid, high). We found that net biodiversity and complementarity effects increased over the elevation gradient, with their strength modified by forest habitat and the identity of litter in mixtures. Complementarity effects at local and landscape scales were greatest for combinations of nutrient‐rich and nutrient‐poor litters, consistent with nutrient transfer mechanisms. By contrast, selection effects were consistently weak and negative at both scales. Selection effects at the landscape level were due mainly to nonrandom overyielding rather than spatial insurance effects. Our findings demonstrate that the mechanisms by which litter diversity affects decomposition are sensitive to environmental heterogeneity at multiple scales. This has implications for the scaling of biodiversity–ecosystem function relationships and suggests that future shifts in environmental conditions due to climate change or land use may impact the functioning of aquatic ecosystems.

中文翻译：

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两个空间尺度的环境异质性影响凋落物多样性-分解关系

生物多样性对生态过程的影响主要在同质条件下的局部尺度上进行了实验评估。为了扩大基于实验的生物多样性功能关系，迫切需要了解这种关系如何受到表征更大空间尺度的环境异质性的影响。在这里，我们测试了 800 米海拔梯度（大尺度环境因素）和森林栖息地（细尺度因素）对凋落物多样性-分解关系的影响。为了更好地理解当地和景观尺度机制，我们将净生物多样性效应划分为适用于每个尺度的互补效应、选择效应和保险效应。我们在模拟天然树洞的水生微观世界中组装了不同的垃圾混合物，在森林栖息地（边缘、内部）和海拔（低、中、高）内嵌套的块中复制混合物。我们发现，净生物多样性和互补效应随着海拔梯度的增加而增加，其强度因森林栖息地和混合物中凋落物的特性而改变。对于营养丰富和营养贫乏的凋落物的组合，局部和景观尺度上的互补效应最大，这与营养转移机制一致。相比之下，选择效应在两个尺度上都始终较弱且呈负值。景观层面的选择效应主要是由于非随机超产而不是空间保险效应。我们的研究结果表明，凋落物多样性影响分解的机制对多个尺度的环境异质性敏感。这对生物多样性与生态系统功能关系的扩展具有影响，并表明未来由于气候变化或土地利用而导致的环境条件变化可能会影响水生生态系统的功能。