Leaf Traits and Photosynthetic Light Response of Quercus Suber L. Seedlings Grown in a Combination of Light and Water Regimes

The aim of this study is to investigate the effects of two important factors: light and water availability on the leaf characteristics and the growth of plants. Seedlings of Quercus suber were grown under controlled conditions (greenhouse) with three light treatments (100, 27 and 3 % of incident light, open, shade and deep shade; respectively) and with daily irrigation. Since middle spring, one half of the seedlings were not watered, so we had two water treatments (water and no water) within each light treatment. We studied the photosynthetic response to light by light curves using an IRGA (infra red gas analyser). Leaves under deep shade showed lower values of light compensation point (LCP), light saturation point (LSP), photosynthetic and respiration rates per leaf area (Rarea, Aarea), N and C content per leaf area (Narea y Carea) and leaf area than leaves under shade or open. However, leaves under deep shade showed a higher photosynthetic rate per unit dry mass (Amass), specific leaf area (SLA), and N concentration than leaves in shade or full light treatments. Water limitation induced a lower quantum yield (Φ), LSP, photosynthetic and respiration rate (per unit area or dry mass), gsarea, N concentration (per unit area or dry mass), photos-ynthetic nitrogen use efficiency (PNUE) and chlorophyll index. However, the leaves of plants under water limitation showed a higher water use efficiency (WUE). An interesting result was that plants under deep shade treatment did not show any differences between water and non-watered treatments in physiological traits, possibly indicating a beneficial effect of deep shade on drought resistance. The simulation of carbon balance at leaf level was very well correlated with the relative growth rates (RGR) of seedlings, indicating that the leaf characteristics (variables obtained by the light curves and SLA) may be a good predictor of the relative growth rate under contrasting light and water conditions.