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.