Hydraulic conductance of leaves correlates with leaf lifespan: implications for lifetime carbon gain

Summary• Previous research suggests that the lifetime carbon gain of a leaf is constrained by a tradeoff between metabolism and longevity. The biophysical reasons underlying this tradeoff are not fully understood. • We used a photosynthesis–leaf water balance model to evaluate biophysical constraints on carbon gain. Leaf hydraulic conductance ( K Leaf ), carbon isotope discrimination (Δ 13 C), leaf mass per unit area (LMA) and the driving force for water transport from stem to leaf (ΔΨ Stem–Leaf ) were characterized for leaves spanning three orders of magnitude in surface area and two orders of magnitude in lifespan. • We observed positive isometric scaling between K Leaf and leaf area but no relationship between Δ 13 C and leaf area. Leaf lifespan and LMA had minimal effect on K Leaf per unit leaf area, but a negative correlation exists among LMA, lifespan, and K Leaf per unit dry mass. During periods of leaf water loss, ΔΨ Stem–Leaf was relatively constant. • We show for the first time that K Leaf, mass , an index of the carbon cost associated with water use, is negatively correlated with lifespan. This highlights the importance of characterizing K Leaf, mass and suggests a tradeoff between resource investment in liquid phase processes and structural rigidity.