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.

Keywords:

• Alleviation
• Arbuscular mycorrhizal fungi
• Heavy metal
• Mn oxidation
• Mn reduction
• Phosphorus

Acknowledgments

This research was granted by Fundação de Amparo à Pesquisa do Estado de São Paulo—FAPESP (process number 98/02960-2). The authors wish to thank Denise L.C. Mescolotti and Luís F. Baldesin at the Laboratory for Soil Microbiology ESALQ/USP Brazil, for their technical assistance during the installation, conduction, and analysis of the experiments.