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

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.