The selenium cycle in three species of Astragalus.
1990
Cowgill U.M.
The objective of this study was to determine the distribution of Se in rainfall in two sites in the arid regions of western Colorado that also supported accumulator species of the genus Astragalus (milk vetch). In addition it was of interest to discover the selenium (Se) cycle in members of this genus. To elucidate the Se cycle in these perennials, samples of plants and soils were collected throughout several growing seasons. Se was not detected (<2 micrograms/L) in any of 12 rainstorms sampled. Nor was any Se found in rain falling through nonaccumulator plants. All the Se detected in rain falling through accumulators was water soluble and most of the Se in leaves of these plants was also water soluble (90-92%). Accumulator plants underwent a progressive loss of Se throughout the growing season beyond the full bloom stage. Prior to the initiation of the following year's growing season, the Se content of accumulator plants was <5 microgram Se/g. During years of adequate rainfall the soils beneath the accumulator plants increased in Se content reaching a peak in the early spring. Soils beneath nonaccumulator plants varied little in their total Se content during the growing season.
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