Mycorrhizal Dependency and Nutrient Uptake by Improved and Unimproved Corn and Soybean Cultivars

Plants in nutrient-deficient soils often benefit when colonized by vesicular-arbuscular mycorrhizal fungi (VAMF). Plants vary, however, in responsiveness or mycorrhizal dependency (MD). The objective of this work was to evaluate MD within corn and soybean cultivars. Three improved and three unimproved corn (Zea mays L.) and three improved and two unimproved soybean [Glycine soja Siebold & Zucc. and Glycine max (L.) Merr.] cultivars were evaluated for growth response, nutrient uptake (N, P, K, Ca, Mg, and Zn), and root phosphatase activity. Greenhouse studies were conducted with VAMF (Gigaspora margarita or Glomus intraradices) and without inoculation in a Iow-P soil. The VAMF colonization of roots with inoculation ranged from 62 to 87% for soybean and 49 to 68% for corn. Soybean had a higher MD than corn, but considerable variation occurred within soybean cultivars. Relative growth of the two unimproved soybean cultivars was significantly greater with VAMF colonization than without (Soja, >1900%; Mandarin, >400%). Among improved cultivars, relative growth was less enhanced with colonization (BSR 201, Richland, and Swift cultivars averaged ≈ 200% greater growth with VAMF than without VAMF colonization). An unimproved corn cultivar, Reid Yellow Dent, was unresponsive to mycorrhizal colonization, whereas another unimproved cultivar, Argentine Pop, increased growth 400% with colonization. Total uptakes of N, P, K, Ca, Mg, and Zn were significantly greater (P < 0.001) in mycorrhizal plants, but the concentrations (mg g⁻ˡ) of N, Mg, and Ca were lower in mycorrhizal plants than in nonmycorrhizal plants. These results suggest that considerable variability exists in MD of corn and soybean cultivars when grown in P-deficient soils, and the variability extends across both improved and unimproved cultivars. Contribution from the Dep. of Agronomy, Iowa State Univ., Journal Paper no. J-15497 of the Iowa Agric. Home Econ. Exp. Stn., Ames, IA. Project no. 3155.