The ‘hydrology’ of leaves: co-ordination of structure and function in temperate woody species

The hydraulic conductance of the leaf lamina ( K lamina ) substantially constrains whole-plant water transport, but little is known of its association with leaf structure and function. K lamina was measured for sun and shade leaves of six woody temperate species growing in moist soil, and tested for correlation with the prevailing leaf irradiance, and with 22 other leaf traits. K lamina varied from 7.40 ¥ 10 5 kg m 2 s 1 MPa 1 for Acer saccharum shade leaves to 2.89 ¥ 10 4 kg m 2 s 1 MPa 1 for Vitis labrusca sun leaves. Tree sun leaves had 15–67% higher K lamina than shade leaves. K lamina was co-ordinated with traits associated with high water flux, including leaf irradiance, petiole hydraulic conductance, guard cell length, and stomatal pore area per lamina area. K lamina was also co-ordinated with lamina thickness, water storage capacitance, 1/mesophyll water transfer resistance, and, in five of the six species, with lamina perimeter/area. However, for the six species, K lamina was independent of inter-related leaf traits including leaf dry mass per area, density, modulus of elasticity, osmotic potential, and cuticular conductance. K lamina was thus co-ordinated with structural and functional traits relating to liquid-phase water transport and to maximum rates of gas exchange, but independent of other traits relating to drought tolerance and to aspects of carbon economy. Key-words : hydraulic architecture; hydraulic conductivity; hydraulic resistance; leaf water storage; specific leaf area; stomatal conductance.