Attenuation of Manganese-Induced Toxicity in Leucaena leucocephala Colonized by Arbuscular Mycorrhizae

Abstract

The use of arbuscular mycorrhizal fungi (AMF) is considered an important strategy to bioremediate contaminated soil by heavy metals. However, the mechanisms used by AMF to attenuate plant toxicity, caused by the higher manganese (Mn) concentrations in the soil, remain poorly understood. We analyzed the influence of Mn on Leucaena leucocephala development and tolerance inoculated with different AMF species (Claroideoglomus etunicatum, Acaulospora scrobiculata and native AMF). In a greenhouse experiment, we exposed the plant to increasing levels of Mn (0, 100, 200, and 400 mg kg−1) in the soil, during 60 days. Higher Mn levels reduced shoot and root dry mass, AMF spore abundance in soil, and mycorrhizal colonization. However, the inoculated plants were lower affected by the Mn increases in the soil, evidencing phytoprotective effect promoted by the AMF. In addition to higher Mn contents in the roots and lower Mn contents in the shoots, inoculated plants with native AMF and C. etunicatum showed increase in P content in the shoots of 34.4% and 21.8% and decrease in leaf toxicity of 65.15% and 34.74%, respectively, as compared with the control treatment. The scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis allowed us in detecting Mn on the surface of the spores, which varied with AMF species, acting as a biological barrier to reduce phytotoxicity and increase plant tolerance to Mn. Together, our results suggest that AMF colonization in Leucaena leucocephala attenuates Mn toxicity symptoms and maximizes its development, increasing its tolerance to high concentrations of this element in the soil.