Monday, November 13, 2006

Stimulated Rhizodegradation of Atrazine by Selected Plant Species.

Chung-Ho Lin1, Robert Lerch2, John Shurts3, Harold Garrett3, and Milon F. George4. (1) University of Missouri, Center for Agroforestry, 203ABNR Bldg, Columbia, MO 65211-7250, (2) USDA-ARS, USDA-ARS, 1406 Rollins St. Rm. 265, Columbia, MO 65211-0001, (3) Landmark Realty of Illinois LLC, 2280 Timber Ridge Rd., Princeton, IL 61356, (4) Center for Agroforestry, University of Missouri-Columbia, 203 ABNR Natural Resources Building, University of Missouri-Columbia, Columbia, MO 65211

The efficacy of vegetative buffer strips (VBS) in intercepting herbicides from surface runoff is related to the ability of plant species to promote rapid herbicide degradation.  A walk-in growth chamber study was conducted to investigate the rhizodegradation of 14C labelled atrazine and the relationship of degradation with soil enzyme activities in the rhizosphere of eight selected plant species.  The plant species including 1) switchgrass, 2) eastern gammagrass, 3) tall fescue, 4) orchardgrass, 5) smooth bromegrass, 6) ryegrass, 7) Illinois bundle flower and 8) hoary tick-trefoil were grown in pots containing Mexico silt loam. Pots containing soil without plants were used as controls. 14C-atrazine was applied to soil after plants were established. Rates of atrazine degradation in plant rhizospheres were significantly enhanced by 84 to 260%. Among the plant species, eastern gammagrass showed the highest capability for promoting bio-degradation of atrazine in the rhizosphere.  More than 90% of atrazine was degraded in rhizosphere of eastern gammagrass as compared to 24% in the control after 100 days of incubation.  The mineralization rates of atrazine was more closely correlated with the soil enzyme activities for β-glucosidase (BGLUS; r = 0.857) and dehydrogenase (DHG; r = 0.763) than with fluorescein diacetate hydrolysis (FDA; r = 0.494).  Dealkylation of atrazine strongly correlated with increased enzymatic activities of BGLUS (r = 0.96), DHG (r = 0.842) and FDA hydrolysis (r =0.702). The incorporation of eastern gammagrass into VBS designs may significantly promote the degradation of atrazine transported to the VBS. Microbial parameters widely used for assessment of soil quality, e.g., DHG and BGLUSD activities, are promising as useful tools for evaluating the overall rhizodegradation potential of various vegetative buffer designs for atrazine remediation