Changes in manganese uptake and translocation by mycorrhizal soybean under increasing Mn doses

Under certain circumstances, Mn toxicity may be alleviated in mycorrhizal plants. Direct and indirect mechanisms can be involved in this process. Our objective was to evaluate the intrinsic effect of arbuscular mycorrhizal fungi (AMF) on the uptake and translocation of Mn by soybean plants. Initially, three AMF were tested to determine their capacity in enhancing plant growth under Mn excess. Glomus macrocarpum was most efficient at protecting plants against Mn excess, as a result of a higher Mn retention in the roots and lower translocation to the shoots. The symbiosis with Gigaspora margarita was inefficient and restricted plant growth. In a second experiment, we used a Mn-tolerant and a Mn-susceptible soybean cultivar, with and without G. macrocarpum, to investigate if there is an increase of Mn oxidation in roots of mycorrhizal plants. No effect of mycorrhiza on Mn oxidation in the roots was detected, but at the rate of 15 mg kg(-1) of Mn, the mycorrhizal plants presented a greater Mn root content. There was a cultivar effect, which caused a higher content of oxidized Mn in the roots of the tolerant one.