TRANSPIRATION DYNAMICS IN CADMIUM-TREATED SOYBEAN (GLYCINE-MAX L) PLANTS

Soybean (Glycine max L.) plants, cv Richland, were grown during 30 day s in a nutrient solution. After this period the plants were treated wi th a 50 mu M Cd(NO3)(2) solution. Sap flow rate and stomatal conductan ce were monitored during 4 consecutive days; at the end of this period relative water content and stomatal width and length were determined on fully expanded leaves. On the second day from the Cd treatment sap, flow rate and stomatal conductance in the treated plants were reduced to 60 % of the control plants. Stomatal conductance kept on decreasin g up to the fourth day. Cadmium decreased the leaf relative water cont ent and the reduction in the stomatal closure was supported by an incr ease in the L/W ratio of the stomata. Root water uptake should be the primary mechanism reduced by Cd stress in soybean, and this reduction is consistent with the decrease in transpiration rate and with the sto matal closure.