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 (K_leaf) and resulted in minor, if at all, changes in the water potential causing 50% decline in K_leaf (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 K_leaf 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.

叶片大小的变化已被证明会显着影响叶片的水硬性，进而影响植物的光合作用和生产力。在这项研究中，我们从四个咖啡种类（Coffea spp。）中选择了五种基因型，这些植物的单个叶面积（从25到280 cm ²）形成了鲜明对比，以测试叶面积的变化是否会导致解剖结构的改变并最终改变叶的水力功能。叶面积的增加与木质部的解剖特征有关，例如较低的大静脉密度，较高的导管数量和导管直径以及较低的细胞壁厚与导管直径之比[（t / b）³]在中肋木质部中。但是，此类修改与叶片水力传导率（K_叶片）的变化无关，并且导致水势的微小变化（如果有的话），导致K_叶片下降50％（P ₅₀），这表明咖啡的叶子尽管叶面变化很大，但这些树种具有非常相似的水力特性。我们提出，较大的咖啡叶中主静脉密度的下降可能通过中脉中木质部导管数量和尺寸的增加而得到平衡，与较小的叶相比，导致相似的K_叶。最后，我们证明了C. racemosa植物的P ₅₀最低以及较高的（t / b）³，应将其视为旨在提高咖啡植物耐旱性的育种者的推定候选人。