Modulation of leaf attributes and water use efficiency in Quercus suber along a rainfall gradient

The aim of our study was to assess the intraspecific variation of a range of leaf attributes and carbon isotope discrimination (Delta), in Quercus suber, along an 800 mm rainfall gradient in Portugal. We measured specific leaf area (SLA), leaf thickness (LT) and density, and used leaf carbon isotope content as an integrated record of water use efficiency. The values of SLA of Q. suber were strongly, positively correlated with rainfall, decreasing as rainfall decreased. This reduction was mainly driven by LT, which was tightly correlated with SLA (R = -0.80, P < 0.001), and steadily increased with declining rainfall. The significant increase in carbon isotope discrimination towards the wetter end of the gradient, with a difference of 4.2aEuro degrees in Delta between the two extremes, suggests a strong adjustment of leaf gas exchange to water availability. Leaf changes associated with precipitation in Q. suber thus seem to influence water economy, since reduction of SLA with the increase of LT with aridity improves water use efficiency. These data suggest that this evergreen tree species relies on its foliage plasticity and physiology to overcome water shortage.