Salinity effects on the stomatal behaviour of grapevine

SUMMARY An investigation of the time‐course of inhibition of photosynthesis in salt‐stressed grapevine (Vitis vinifera L.) leaves revealed two types of stomatal behaviour. Up to tissue concentrations of 165 mM chloride the inhibition was due to a uniform decrease in stomatal conductance, as indicated from autoradiograms of 14CO2 fixation and no change in the relationship of assimilation to calculated intercellular partial pressure of CO2 (A‐C1) compared with control plants. The occurrence of non‐stomatal inhibition of photosynthesis at higher levels of leaf chloride, suggested by a decline in the slope of the calculated (A‐C1) relationship, was associated with non‐uniform 14CO2uptake over the leaf surface similar to that previously observed for ABA‐treated and water‐stressed grapevine leaves where non‐stomatal inhibition of photosynthesis was shown to be an artifact arising from non‐uniform stomatal behaviour. These observations also provide an explanation for the stimulation of photorespiration during salt stress.