Atrazine tolerance of grass species with potential for use in vegetated filters in Australia.
The response of introduced (Pennisetum clandestinum) and native (Stipa aristiglumis, Themeda australis [Themeda triandra], Danthonia spp.) grasses to the herbicide atrazine was determined. The plants are potential vegetation filters (biofilters) designed to reduce chemical loads in agricultural runoff. The response was detected by photosynthetic inhibition using leaf chlorophyll fluorescence. With continuous short-term (14 days) application of atrazine in sand cultures, P. clandestinum showed the greatest tolerance, regardless of the dose (20-500 µg/litre). In a clay vertosol soil in the glasshouse, all 4 species were tolerant to long term (84 days) application of 3 successive doses of simulated run-on, each dose containing 100 µg/L atrazine, a concentration which is comparable to the highest reported in runoff from agricultural land in Australia. Even with a subsequent single atrazine dose of ∼5000 µg/litre, the established plants showed signs of quick recovery (7-21 days) to normal photosynthetic activity. In a field experiment conducted in Hawkesbury region, New South Wales, Australia, with simulated run-on, P. clandestinum did not show a significant response to repeated doses of atrazine (up to 1000 µg/litre) applied to a sandy soil. However, a subsequent single dose of 5000 µg/litre resulted to significant effects, from which plants soon recovered. Although damage from atrazine can be demonstrated with continuous dosage in non-adsorbing media, the tolerance of all 4 species to repeat doses of atrazine in soil culture shows they may be used confidently for biofiltering purposes. P. clandestinum was especially tolerant.