Eucalypt is highly efficient at growing in nutrient-poor soils, but little is known about the role of ectomycorrhizas and organic acids in nutrient uptake and storage under field conditions. Oxalic acid production and its relationships with Ca, P, K, and Mg concentrations were evaluated in the ectomycorrhizas and fine lateral roots of a 2.5 year-old Eucalyptus grandis x Eucalyptus urophylla hybrid grown in a mountainous area at Viçosa, MG, Brazil. Oxalic acid concentrations were also evaluated in rhizospheric, non-rhizospheric, and ectomycorhizospheric soil. Mycorrhizal colonization was highest in a slope area with limited nutrient availability and high Al saturation. The oxalic acid concentration was 324.6 mg kg-1 in the leaves; 208.3 mg kg-1 in ectomycorrhizas; and 183.1 mg kg-1in non-mycorrhizal fine lateral roots. The concentrations in the soil were highest in the ectomycorhizospheric soil, 183.7 mg kg-1, followed by the rhizospheric soil, 134.3 mg kg-1, and finally, by the non-rhizospheric soil, 76.0 mg kg-1. The highest oxalic acid and P concentrations in the ectomycorrhizas found in the hilltop area, 117.3 mg kg-1and 6.3 mg kg-1, respectively, suggest that the population of ectomycorrhizal fungi in this area plays an important role in nutrient solubilization and supply to the host plant. No significant positive correlations were observed between oxalic acid production and Ca concentrations in the fine lateral roots and ectomycorrhizas of the eucalypt trees.
rhizosphere; root exudates; potassium; phosphorus; magnesium
