When smaller is better: leaf hydraulic conductance and drought vulnerability correlate to leaf size and venation density across four Coffea arabica genotypes

Leaf hydraulic conductance (K-leaf) and drought vulnerability in terms of leaf water potential inducing 50% loss of K-leaf (P-50), were assessed in four genotypes of Coffea arabica L. We tested three hypotheses: (1) leaf P-50 is lower in small leaves with higher vein densities; (2) lower P-50 translates into lower K-leaf, limiting gas exchange rates and higher leaf mass per unit area (LMA); (3) P-50 values are coordinated with symplastic drought tolerance. We found partial support for Hypotheses 1 and 3, but not for Hypothesis 2. Significant correlations existed among leaf size, vein network and drought resistance. Smaller leaves displayed higher major vein density, higher K-leaf and more negative P-50. K-leaf was correlated with leaf gas exchange rates. A negative relationship was observed between K-leaf and LMA, whereas P-50 was found to be positively correlated with LMA. Across coffee genotypes, reduced leaf surface area and increased vein density shifts P-50 towards more negative values while not translating into higher LMA or lower K-leaf. Breeding crop varieties for both increased safety of the leaf hydraulic system towards drought-induced dysfunction and high gas exchange rates per unit of leaf area is probably a feasible target for future adaptation of crops to climate change scenarios.