SELENIUM TOXICITY IN PERENNIAL RYEGRASS AND WHITE CLOVER

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Abstract
Summary: Shoot concentrations of Se associated with a 10% reduction in dry matter yield were established for perennial ryegrass (Loliumperenne L.) and white clover (Trifolium repens L.) grown in sand culture. Selenite– treated plants had lower shoot concentrations of Se than those treated with selenate; the critical toxic values associated with a 10% reduction in growth were 48 and 320μg Se g− 1 dry matter shoots for ryegrass plants, and 160 and 330μeg1 dry matter shoots for white clover plants, respectively. Differences in the mode of absorption of selenite and selenate, and in the distribution and chemical form of Se found in the plant after absorption, probably account for this disparity in toxicity. While both selenate and selenite increased the Se concentration in the tissues of the plants to high levels, a greater proportion of the absorbed Se was transported to the shoots of the selenate‐treated plants than of those treated with selenite. Increasing supplies of selenate were associated with a reduction in chlorophyll content. Contrary to the concept of a common uptake mechanism in the roots for selenate and sulphate, increasing supplies of selenate had a synergistic effect on S concentrations in the shoots rather than the expected antagonistic effect.