Manganese accumulation and tolerance in Eucalyptus globulus and Corymbia citriodora seedlings under increasing soil Mn availability

Abstract

Manganese (Mn) is a nutrient that can cause phytotoxicity if above a threshold concentration. Acid soils are prone to excessive Mn levels that under certain environmental conditions may increase availability and exacerbate deleterious effects on plants. Apart from oxidative stress, excess Mn usually affects photosynthetic apparatus. Nonetheless, some plants are known to tolerate high Mn contents without negative consequences. We carried out a greenhouse experiment with two eucalypt species (Eucalyptus globulus and Corymbia citriodora), treated with four Mn additions in the soil substrate (0, 50, 150 and 300 mg kg−1) for 18 weeks. Before harvest, shoot height and the chlorophyll a fluorescence parameters were assessed, then leaves, stems and roots were sampled, weighted and nutrients determined. Manganese addition increased height for both species while biomass production remained unchanged, even though foliar concentrations ranged from 600 to 800 mg kg−1 at the highest Mn in soil. High root-to-shoot translocation of Mn was observed, yet—contrary to our hypothesis—photochemical efficiency of photosystem II was barely affected, except for the slight decrease in C. citriodora under 300 mg kg−1 Mn. The capacity to accumulate high Mn in photosynthetic tissues without chlorophyll damage seems to be a feature of Mn tolerant species. Nutritional imbalances such as magnesium decrease due to Mn exposure was observed, but not enough to cause deficiency. Both eucalypt species were therefore tolerant to high Mn concentrations in soil, especially E. globulus, and have the potential to be employed in reforestation/afforestation of lands with high risk of Mn phytotoxicity.