Nonstomatal inhibition of photosynthesis at low water potentials in intact leaves of species from a variety of habitats.

Mesophyll resistance to CO(2) uptake was calculated from gas exchange data on intact leaves of 12 species of woody plants. Plants studied were native to habitats ranging from streamsides to deserts. Gas exchange measurements were made at light saturation and constant temperature to eliminate possible effects of light and temperature on estimates of mesophyll resistance. Cuticular transpiration was measured and used in calculation of stomatal resistances from whole leaf transpiration rates. In all species examined, an increase in mesophyll resistance was observed as leaves dried. The increase in mesophyll resistance in all cases occurred at the same water potential as the initial decline in net photosynthesis, and was accompanied by an increase in stomatal resistance.