ADDITIVE, PROTECTIVE, AND SYNERGISTIC EFFECTS ON PLANTS WITH EXCESS TRACE ELEMENTS

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Abstract
Bush bean plants were grown 15 days in solution culture to test whether or not multiple trace elements that result in little or no apparent stress when applied alone would result in more or less stress when applied together. Prior experience had indicated these possibilities, and the matter is of considerable concern in establishing threshold levels for excesses of some trace elements in the environment. Levels of cadmium (5 X 10−7M), copper (10−5M), zinc (5 X 10−5M), manganese (10−4M), cobalt(10−6M), and nickel (10−6M) were applied singly; cadmium, copper, and zinc together; manganese, cobalt, and nickel together; and all six combined. Little or no stress was expected for some of the single elements; the yield depression in dry weight of trifoliate leaves for the experiment was 0 percent for cadmium, 2 percent for copper, 43 percent for zinc, 32 percent for manganese, 0 percent for cobalt, and 4 percent for nickel. For cadmium, copper, and zinc together the depression was 46 percent; for manganese, cobalt, and nickel, 23 percent, and for all six, 85 percent. Additive, protective, and synergistic effects were involved, although induced iron deficiency complicated the results for all six elements combined. The results indicate that even if the concentration of at least some elements is too low to have any visual effects, they can have important consequences if other trace element stresses are simultaneously present. Bush bean plants were grown 15 days in solution culture to test whether or not multiple trace elements that result in little or no apparent stress when applied alone would result in more or less stress when applied together. Prior experience had indicated these possibilities, and the matter is of considerable concern in establishing threshold levels for excesses of some trace elements in the environment. Levels of cadmium (5 X 10−7M), copper (10−5M), zinc (5 X 10−5M), manganese (10−4M), cobalt(10−6M), and nickel (10−6M) were applied singly; cadmium, copper, and zinc together; manganese, cobalt, and nickel together; and all six combined. Little or no stress was expected for some of the single elements; the yield depression in dry weight of trifoliate leaves for the experiment was 0 percent for cadmium, 2 percent for copper, 43 percent for zinc, 32 percent for manganese, 0 percent for cobalt, and 4 percent for nickel. For cadmium, copper, and zinc together the depression was 46 percent; for manganese, cobalt, and nickel, 23 percent, and for all six, 85 percent. Additive, protective, and synergistic effects were involved, although induced iron deficiency complicated the results for all six elements combined. The results indicate that even if the concentration of at least some elements is too low to have any visual effects, they can have important consequences if other trace element stresses are simultaneously present. © Williams & Wilkins 1982. All Rights Reserved.