Data from: How do leaf trait values change spatially and temporally with light availability in a grassland diversity experiment?

Complementarity in light use might increase light exploitation and could be an important mechanism explaining the coexistence of multiple species in plant communities of increasing diversity. We measured vertical light profiles and leaf traits related to light acquisition and light use in 40 mixtures of varying species richness (SR, 2, 4, 8 and 16) and functional group richness (FR, 1-4) in a large grassland biodiversity experiment at five different times during the growing season. Light attenuation within the canopy differed significantly among mixtures of varying SR at peak biomass, with 40% in 2-species mixtures and up to 80% in 16-species mixtures. In contrast, increasing SR did not affect light attenuation at the beginning of the growing season or during regrowth after mowing, when large fractions of incoming radiation reached the ground level. These patterns suggested the presence of highly variable light niches over space and time. Trait expression differed among functional groups (except specific leaf area (SLA)) and varied within the growing season. However, we found no direct effect of increased SR or FR on the expression of leaf traits, except for positive species richness-effects on SLA at peak biomass time. SLA and stomatal conductance increased and leaf dry matter content decreased at lower light at leaf height, while leaf greenness was independent of relative light availability. Dissimilarity of leaf traits (except SLA) at the community level increased with increasing SR. Thus, our results suggest that after accounting for light availability, which was driven by SR and time of year, variations in leaf trait expression within the grassland canopies did not depend on SR, but rather on functional group identity and time of year. Consequently, increased complementarity in light use at higher plant diversity is due to presence of more species with different leaf trait expression and trait variation in response to the actual light environment.

光能利用互补性或可提升光能利用效率，且可能是解释物种多样性递增的植物群落内多物种共存现象的重要机制。本研究基于一项大型草地生物多样性实验，于生长季的5个不同时间节点，对40个物种丰富度（species richness, SR）分别为2、4、8与16、功能群丰富度（functional group richness, FR）为1~4的植物混合群落，测定了其垂直光剖面以及与光能获取、利用相关的叶片性状。在生物量峰值期，不同SR处理的混合群落冠层内光衰减差异显著：2物种混合群落的光衰减率为40%，16物种混合群落则可达80%。与之相反，在生长季初期或刈割后的恢复期，由于大量入射辐射可抵达地面，SR的提升并未对冠层光衰减产生显著影响。上述结果表明，光生态位在空间与时间维度上存在高度可变的特征。不同功能群的叶片性状表达存在差异（比叶面积（specific leaf area, SLA）除外），且性状表达随生长季进程发生波动。然而，除生物量峰值期物种丰富度对SLA存在正向效应外，SR或FR的提升并未对叶片性状表达产生直接影响。在叶位光照水平更低的区域，SLA与气孔导度升高，叶片干物质含量则随之降低；叶片绿度与相对光可用性并无关联。群落水平的叶片性状相异性（SLA除外）随物种丰富度升高而增大。综上，本研究结果表明，在考虑由SR与生长季时间节点所驱动的光可用性后，草地冠层内的叶片性状表达差异并不依赖于物种丰富度，而是取决于功能群属性与生长季时间节点。因此，植物多样性更高时光能利用互补性的提升，源于存在更多具备差异化叶片性状表达，且能响应实际光环境产生性状变异的物种。