Data from: Across species-pool aggregation alters grassland productivity and diversity

Plant performance is determined by the balance of intra- and interspecific neighbors within an individual's zone of influence. If individuals interact over smaller scales than the scales at which communities are measured, then altering neighborhood interactions may fundamentally affect community responses. These interactions can be altered by changing the number (species richness), abundances (species evenness), and positions (species pattern) of the resident plant species, and we aimed to test whether aggregating species at planting would alter effects of species richness and evenness on biomass production at a common scale of observation in grasslands. We varied plant species richness (2, 4, or 8 species and monocultures), evenness (0.64, 0.8, or 1.0), and pattern (planted randomly or aggregated in groups of four individuals) within 1 × 1 m plots established with transplants from a pool of 16 tallgrass prairie species and assessed plot-scale biomass production and diversity over the first three growing seasons. As expected, more species-rich plots produced more biomass by the end of the third growing season, an effect associated with a shift from selection to complementarity effects over time. Aggregating conspecifics at a 0.25-m scale marginally reduced biomass production across all treatments and increased diversity in the most even plots, but did not alter biodiversity effects or richness–productivity relationships. Results support the hypothesis that fine-scale species aggregation affects diversity by promoting species coexistence in this system. However, results indicate that inherent changes in species neighborhood relationships along grassland diversity gradients may only minimally affect community (meter) – scale responses among similarly designed biodiversity–ecosystem function studies. Given that species varied in their responses to local aggregation, it may be possible to use such species-specific results to spatially design larger-scale grassland communities to achieve desired diversity and productivity responses.

植物表现由个体影响域内种内与种间邻体的平衡关系所决定。若个体间相互作用的发生尺度小于群落观测尺度，则改变邻体相互作用可能从根本上影响群落的响应。此类相互作用可通过调控本地植物物种的数量（物种丰富度（species richness））、多度（物种均匀度（species evenness））与空间位置（物种格局（species pattern））加以改变；本研究旨在检验，在草地生态系统的统一观测尺度下，种植时采用物种聚集模式是否会改变物种丰富度与均匀度对生物量生产的影响。本研究在由16种高草草原（tallgrass prairie）物种的移栽苗构建的1×1 m样方内，设置了3个梯度的物种丰富度（2、4、8种及单作群落）、3个梯度的物种均匀度（0.64、0.8、1.0）以及2种物种格局（随机种植或按4株为一组聚集种植），并在首个三个生长季内评估了样方尺度的生物量生产与物种多样性。正如预期，至第三个生长季末期，物种丰富度更高的样方生物量产量更高，该效应随时间推移呈现出从选择效应（selection effect）向互补效应（complementarity effects）转变的特征。在0.25 m尺度下聚集同种个体，会小幅降低所有处理组的生物量生产，并在均匀度最高的样方中提升物种多样性，但并未改变生物多样性效应或丰富度-生产力关系。本研究结果支持如下假说：在该系统中，细尺度（fine-scale）的物种聚集可通过促进物种共存来调控物种多样性。然而，研究结果表明，在采用相似设计的生物多样性-生态系统功能（biodiversity-ecosystem function）研究中，沿草地多样性梯度产生的物种邻体关系固有变化，仅会对群落（米级）尺度的响应产生极小影响。鉴于不同物种对局部聚集的响应存在差异，我们可利用此类物种特异性的研究结果，在空间上设计更大尺度的草地群落，以实现预期的多样性与生产力响应目标。