Response of specific leaf area to light: comparative study of a large species set

Specific leaf area (SLA) is a commonly used proxy for the leaf economy
spectrum in plants, separating species with low-cost leaves (in terms of
carbon) with short lifespan and hence fast turnover from species with
high-cost and long-lived leaves. While SLA is used mainly for
interspecific comparisons, it also varies within species both
ontogenetically and in response to the environment. We hypothesise that
the light signal should play a key role as a driver of plasticity of SLA,
as fast growth of low-cost leaves is essential both for fast capture of
light and shading of potential competitors. We therefore examined
interspecific differences in the SLA plasticity to light in a garden
experiment with 67 herbaceous species grown under six light regimes in
replicated factorial design. We found that intraspecific variation in SLA
was largely driven by photosynthetically active radiation (PAR) with only
minor effect of red/far red ratio (R/FR). The magnitude of SLA response to
light strongly differed among species, with light regime explaining
between 4% to 80% (mean 48%) of the total SLA variation. The effect of
light on SLA had no phylogenetic signal and showed weakly positive
relationship to height (taller plants having stronger response of SLA to
light) and negative to the mean SLA (high-SLA species respond less). This
indicates that taller plants, i.e. those competing for light more
strongly, are able to change their SLA faster in order to keep up in
vertical competition for light. This response is largely driven by the
light energy availability and does not seem to be an active response to
the red/far red signal.