Manganese Toxicity in Mycorrhizal and Phosphorus-Fertilized Soybean Plants

Abstract

The alleviation of manganese (Mn) toxicity by arbuscular mycorrhizal fungi (AMF) in soybean exposed to excessive Mn was evaluated at two points of plant development (45 and 90 days). In order to eliminate the dilution effect that is usually observed in mycorrhizal plants due to better phosphorus (P) nutrition, an additional nonmycorrhizal control that received extra P was included. At 45 days, mycorrhiza increased Mn toxicity symptoms and usually decreased plant growth. At 90 days, mycorrhizal plants reverted this situation and had Mn toxicity alleviation, even when comparing to the control plants that received extra P, in spite of their similar biomasses. Mycorrhizal plants had lower Mn and higher P concentrations in shoots and roots, a condition that contributed to the Mn toxicity alleviation. Stimulation of Mn oxidizing bacteria and suppression of Mn reducing bacteria in the rhizosphere of mycorrhizal soybean plants may have contributed to the lower Mn concentration in these plants.