MAGNESIUM-DEFICIENCY IN EXPANDING LEAVES OF PHASEOLUS-VULGARIS - GAS-EXCHANGE AND NUTRIENT CONCENTRATIONS

Phaseolus vulgaris was cultured either with or without magnesium in an aerated nutrient solution in growth chambers from 21 days after germination. Five days after transfer to Mg-deficient nutrient solution, terminal leaflets of first trifoliate leaves stopped expansion. From the fifth day after transfer, the net assimilation rate, the transpiration rate and the leaf water vapour conductance of first trifoliate leaves of the deficient plants declined. Following resupply of Mg on the seventh day after transfer to the Mg-deficient solution, the assimilation rate increased to 93% by the 12th day, the transpiration rate to 76% and the leaf water vapour conductance to 50% of the control plants.