Rates of Selenium Volatilization among Crop Species

The rate of Se volatilization per plant was measured for 15 crop species grown hydroponically (for 18–48 d depending on the species) in growth chambers. Selenium was supplied as 20 micromolar sodium selenate in 0.25 strength Hoagland's solution. Selenium volatilization was determined by enclosing plants in a Plexiglas plant chamber and trapping the volatile Se emissions in alkaline peroxide traps. The results show that rice ( Oryza sativa L.), broccoli ( Brassica oleracea botrytis L.), and cabbage ( Brassica oleracea capitata L.) volatilized Se at the fastest rates, i.e., 200 to 350 µg Se per m 2 leaf area per day (1500–2500 µg Se kg −1 plant dry wt. d −1 ). Carrot ( Daucus carota L.), barley ( Hordeum vulgare L.), alfalfa ( Medicago sativa L.), tomato ( Lycopersicon esculentum Mill.), cucumber ( Cucumis sativus L.), cotton ( Gossypium hirsutum L.), eggplant ( Solanum melongena L.), and maize ( Zea mays L.) had intermediate rates of 30 to 100 µg Se m −2 d −1 (300–750 µg Se kg −1 d −1 ). Sugarbeet ( Beta vulgaris L.), bean ( Phaseolus vulgaris spp.), lettuce ( Lactuca sativa L.), and onion ( Allium cepa L.) had the lowest rates, i.e., less than 15 µg Se m −2 d −1 (<250 µg Se kg −1 d −1 ). Comparing all plant species, Se volatilization rate was found to be highly correlated with Se concentration in plant tissues; we suggest that the ability of plants to absorb Se may be an important factor contributing to high rates of Se volatilization.