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.