Acúmulo de ácido oxálico e cristais de cálcio em ectomicorrizas de eucalipto

• Autor(a) principal: Gonzalez, Jhon Alexander Zambrano
• Data de Publicação: 2007
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5382
• topic: Ectomicorriza; Oxalato de cálcio; Nutrição mineral; Ácidos orgânicos; Ectomycorrhizas; Oxalate calcium; Mineral nutrition; Organic acidS; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::MICROBIOLOGIA AGRICOLA

This work aimed at evaluating the role of the ectomycorrhizal fungi in the uptake and storage of calcium in Eucalyptus sp., grown for 2.5 years, in a mountainous area in the region of Viçosa, MG. Abundant accumulation of oxalate crystals as grains or druses was observed in 73.7 % of the ectomycorrhizas and fine lateral roots studied. The conspicuous presence of CaOx was observed in 56.2% of the ectomycorrhizae and in 17.5% of the nonmycorrhizal lateral fine roots, evidencing the role of the ectomycorrhizal association in the storage of calcium in the roots of Eucalyptus sp. The highest mycorrhizal colonization was observed in the Slope area that presented limited availability of nutrients and high Al saturation. Oxalic acid concentrations decreased in the following order, in mg Kg -1: leaves, 162.3 > ectomycorrhizas, 118.2 > non-mycorrhizal fine lateral roots, 116.0. Oxalic acid concentrations in the soil were higher in ectomycorhizospheric soil with 91.8 mg Kg-1, followed by the rhizospheric soil, with 67.2 mg Kg-1, and, finally, by the non-rhizospheric soil with 38 mg Kg-1. In the ectomycorrhizas collected in the Top area, the higher concentrations of oxalic acid and P, 173.3 mg Kg-1 and 6.35 mg Kg-1, respectively, probably resulted from nutrient solubilization by the ectomycorrhizal fungi associated with the host plants. The larger fraction of the litter layer corresponded to that showing the most advanced level of decomposition, being composed of dark fragments of leaves and branches in direct contact with the soil. Generally, nutrient content in the forest litter, in ka ha-1, decreased as follows: Ca (32.4) > Mg (5.4) > K (4.2) > P (1.7). Ca content in the litter and its low concentration in the soil shows the importance of the litter layer as a Ca reservoir for eucalypts. The highest concentrations and contents of P in the litter were verified in the Top position, however, the activity of acid phosphatases of ectomycorrhizas did not differ among the topographical positions evaluated. Fruit bodies of Laccaria, Pisolithus, Scleroderma, and of an unidentified fungus were observed in the area under study. The examination of the most decomposed litter layer and of the interface soil-litter showed an intense colonization by eucalypt roots, with eight distinct ectomycorrhizal morphotypes, hyphae, rhizomorphs, and basidiomes This work demonstrate that ectomycorrhizal fungi participate in the cycling of the eucalypt forest litter and in the storage of Ca when associated to eucalypt roots.