Jayachandran, Krishnaswamy - IOWA STATE UNIVERSITY
Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 25, 1999
Publication Date: N/A
Interpretive Summary: The herbicides atrazine and trifluralin are applied throughout Midwestern corn and soybean crops to provide control of yield-reducing weeds. Carry-over of herbicide residues in the soil stresses or injures sensitive crops. This research examined the potential effect of mycorrhizal fungi on herbicide uptake by corn and soybeans. These root-colonizing fungi take up mineral nutrients and pass them along to the plant, thus increasing plant growth. However, the ability of these fungi to take up organic molecules, such as herbicides, has not been examined. Our research showed that mycorrhizal fungi do increase herbicide uptake. The fungus extends from the plant root into the soil and takes up the herbicide directly. In situations where phytotoxic herbicide residues are present in the soil, mycorrhizal fungi would enhance uptake, and may increase plant stress. Our increased understanding of the mycorrhizae-herbicide interactions will allow better management of herbicides and decreased risk for farmers.
Vesicular-arbuscular mycorrhizal (VAM) fungi increase root uptake of phosphorus and other minerals, but their role in the uptake of herbicides is not clear. These experiments were conducted to determine the effect of the VAM fungus, Glomus epigaeus (Daniels & Trappe), on the absorption of atrazine and trifluralin by roots of corn and soybean. Herbicide uptake by excised root segments was consistently increased by the VAM fungus. Roots from corn grown for 8 weeks in the greenhouse prior to the experiment took up 25 pM mm**-3 root, whereas, non-mycorrhizal roots took up only 11 pM mm**-3 root. Atrazine and trifluralin uptake by intact root systems of corn and soybeans were also enhanced by VAM formation. In both corn and soybeans, addition of P to the soil did not increase root uptake of herbicide, indicating that P nutrition effects do not account for the effect of the VAM fungi on herbicide uptake. The direct role of VAM hyphae on atrazine uptake was demonstrated using a two-chamber system, where only the fungal hyphae had access to 14C-atrazine-treated soil. Hyphal systems of the fungus were able to remove and transfer 14C-atrazine residues from soil to corn plants. Our results show that the VAM association enhances the uptake of atrazine by corn and soybean roots by direct uptake of the herbicide by the fungal hyphae.