PHYSIOLOGICAL-RESPONSES OF 2 SOYBEAN CULTIVARS TO CADMIUM

Anthropogenic activities are increasing cadmium (Cd) concentrations in agricultural soils. Cadmium can be absorbed by plant roots and modify the physiology of the plant. Carbon exchange rate (CER) and leaf cond uctance to water vapor (g(s)) were measured on the fifth leaf of two s oybean (Glycine max [L.] Merr.) cultivars (Illini insensitive and Rich land sensitive) for 6 consecutive days; Cd(NO3)(2) was added to the hy droponic solution to achieve a final concentration of 50 mu mol. At th e end of the experiment, stomata length and width, mesophyll limitatio n to photosynthesis, root hydraulic conductance, relative water conten t (RWC), and Cd concentration in leaves, stems, and roots were measure d on treated and control plants. Cadmium progressively reduced CER and g(s) to about 50% after 6 d of treatment. This was more evident in Ri chland than in Illini and was not linked with leaf RWC and mesophyll l imitation to photosynthesis. After 6 d, the apparent root hydraulic wa ter conductivity was 67% lower in the Cd-treated plants than in contro ls. The primary mechanism affected by Cd-induced stress in soybean is root water uptake, and this reduction is consistent with the decrease in stomatal opening and conductance, and therefore, in photosynthesis.