Interactions of vesicular arbuscular mycorrhizal fungi, herbicides and crops

Abstract

Experiments were conducted to detemnine the influence of vesicular-arbuscular mycorrhizal (VAM) fungus on root uptake of herbicides. Absorption of atrazine by excised roots of com and soybean colonized with and without the VAM fungus, Glomus epigaeus (Daniels & Trappe) from herbicide solutions was compared. Similarly, trifluralin uptake by excised VAM and non-VAM soybean roots was studied. Herbicide uptake was consistently greater by VAM roots. Atrazine and trifluralin uptake from herbicide solutions were also studied by using whole-root systems of soybean and com, respectively, with and without VAM fungus. Atrazine and trifluralin uptake by intact root systems were enhanced by VAM association, however increase in uptake by mycorrhizal roots was more evident in herbicide absorption by excised roots. The direct role of VAM hyphae on atrazine uptake was studied by using a two-chamber system where only the fungal hyphae had access to the I^C-atrazine-treated soil. Hyphal systems of the fungus were able to remove and transfer ''^C-atrazine residues from soil to corn plants. Our results suggest that the VAM association enhances the uptake of atrazine by com and soybean roots as influenced by the direct uptake of the herbicide by the fungal hyphae. Nomenclature: atrazine, 6-chloro/V-ethyl-A/'-(1-methylethyl)-1,3,5-triazine-2,4-diamine): trifluralin, 2,6-dinitro-A/,/\/-dipropyl-4(trifluoromethyl) benzamine; corn, Zea mays L.; soybean. Glycine max{L) Merr. Additional index words: VAM fungi, Glomus epigaeus, excised roots, external hyphae, atrazine, trifluralin. ^Received for publication and in revised form . Joint contribution of USD AAgric. Res. Serv. and Iowa State Univ. Journal Paper No. of the Iowa Agric. and Home Econ. Exp. Stn., Ames. IA50011. ^Grad. Res. Asst., Dep. Agron. Iowa State Univ., Ames, lA 50011. ^Microbiologist, USDA, Agric. Res. Serv. ^Soil Microbiologist, Dep. Agron. Iowa State Univ., Ames, lA 50011.