Evaluating semiaquatic herbaceous perennials for use in herbicide phytoremediation

Canna x generalis L.H. Bail. (canna), Pontaderia cordata L. (pickerel weed) , and Iris L. x 'Charjoys Jan' ('Charjoys Jan' iris) were exposed to a 5 mg .L-1 suspension of isoxaben or oryzalin or a water control for 9 days. Grow th and photosynthetic responses were monitored throughout treatment and for an additional 22 d after termination of treatment. By the end of the exper iment plant height of pickerel weed was reduced by oryzalin, Isoxaben resul ted in lower height and reduced leaf emergence for all three taxa by the en d of the experiment. Leaf CO2 assimilation (A) and transpiration (E) were l ower for oryzalin-treated canna only 17 and 18 days after treatment, severa l days after treatment had been terminated. Leaf A and E were lower for ory zalin-treated pickerel weed and 'Charjoys Jan' iris for most days after day 17, Isoxaben reduced A and E of all three plants for all days measured exc ept day 6 for 'Charjoys Jan' iris. Lower photosystem II efficiency (Fv/Fm) was found for isoxaben-treated canna from day 5 onward and days 7, 20, and 23 for pickerel weed and 'Charjoys Jan' iris. Rapid reduction in A and Fv/F m for all plants treated with isoxaben indicates a direct effect of isoxabe n on photosynthesis. Reductions in growth and photosynthetic parameters due to oryzalin were minimal for all plants indicating these plants would be u seful in phytoremediation systems where oryzalin is present. However, growt h and photosynthetic parameters were reduced substantially for all plants e xposed to isoxaben indicating the taxa studied would not perform well in ph ytoremediation systems with this level of isoxaben exposure. Chemical names used: isoxaben (N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyly]-2,6-dimethoxy benzamide); oryzalin (4-(dipropylamino)-3,5-dinitrobenzenesulforamide).