Leaf hydraulic properties are decoupled from leaf area across coffee species

Changes in leaf size have been demonstrated to considerably affect leaf hydraulic properties, which in turn impact plant photosynthesis and productivity. In this study, we selected five genotypes from four coffee species (Coffea spp.) with highly contrasting individual leaf areas (from 25 to 280 cm2) to test whether changes in foliar area result in anatomical alterations and ultimately changes in leaf hydraulic function. Increasing leaf area was associated with xylem anatomical traits, such as lower major vein density, higher number of conduits and conduit diameter, and lower cell wall thickness-to-conduit diameter ratio [(t/b)3] in the midrib xylem. Such modifications, however, were not associated with changes in leaf hydraulic conductance (Kleaf) and resulted in minor, if at all, changes in the water potential causing 50% decline in Kleaf (P50), which demonstrate that leaves of coffee species have very similar hydraulic properties despite considerable variations in foliar area. We propose that declines in major vein density in larger coffee leaves are potentially balanced by increases in xylem conduit number and dimensions in the midrib, resulting in similar Kleaf when compared with smaller leaves. Finally, we demonstrate that C. racemosa plants have both the lowest P50 and the higher (t/b)3, and it should be considered as a putative candidate for breeders aiming at increasing drought tolerance in coffee plants.