Nonstomatal Inhibition of Photosynthesis at Low Water Potentials in Intact Leaves of Species from a Variety of Habitats

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Abstract
Mesophyll resistance to CO2 uptake was calculated from gas exchange data on intact leaves of 12 spp. of woody plants [Alnus oblongifolia, Fraxinus pennsylvanica ssp. velutina, Pinus ponderosa, Juniperus deppeana, Vauquelinia californica, Simmondsia chinensis, Acacia greggii, Larrea divaricata, Alnus rugosa, Fraxinus pennsylvanica, Acer saccharum and Pinus rigida]. 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.