This study describes the aluminum (Al) accumulation in relation to macronutrient and micronutrient elements in 19 Melastomataceae species in the Guayana Region in Venezuela. The purpose was to investigate the Al accumulation in four tribes and different life forms. Aluminum accumulation was predicted in the basal tribes Miconieae and Merianieae in contrast to the derived tribes and herbs from any tribe, which generally do not accumulate Al. The survey was done in a vegetation continuum, which includes a savanna shrubland, a palm-swamp community, and an evergreen forest in the Guayana region in southeastern Venezuela. The highest value of soil Al concentration was found in the savanna shrubland, where ten lignified Miconiae and one Merianeae Al accumulators were present. At the forest, the site with highest soil acidity, four Al-accumulator tree species from Miconiae were found. Miconia lepidota showed similar Al foliar concentrations in the savanna shrubland and forest, but foliar Ca was lower in the forest, even though it was the site with highest Ca in the soil. At the palm-swamp community, the Melastomeae shrub Macairea pachyphylla was found with an Al concentration of 0.59 g kg -1 in leaves and 0.16 g kg -1 in bark. At the same site, Al accumulation occurred in one Microlicieae species, one Miconieae species, and in the Melastomeae herbs Pterogastra divaricata
The purpose of this study was to investigate the nutritional status of Pteridium caudatum (bracken fern) in a Neotropical region where this species occurs in acid leached soils. In this region there is a high availability of Al in soluble toxic forms, rendering P. caudatum an important weed associated with wildfire regimes. Water-soluble Ca, exchangeable Ca fraction, Ca bound to pectate + phosphate, and bound to oxalate were evaluated from P. caudatum sampled from a burned parcel of land 94 and 270 days after an accidental fire, as well as from an unburned control parcel. Both sites were located in a tropical secondary savanna community in a successional mosaic of a cloud forest. The concentrations of total Ca, N, P, K, Mg, Fe, Mn, Zn, Cu, Ni and Al, and their distribution in the plant organs were investigated. The study addressed the hypothesis thai shoots should show low concentrations of Ca because a low cation capacity exchange has been reported in roots of Pteridium. We expected a low water-soluble Ca fraction because bracken has been defined in the literature as a non-calcicole plant. The exchangeable fraction and pectate + phosphate bound Ca constituted 60 to 85% of the total Ca in pinnae and rhizomes, while the oxalate bound Ca constituted only 3 to 14% of the total Ca. Concentrations of Al as high as 248.3 mmol kg -1 were found in roots. Pinnae showed only 84.53 mmol Ca kg -1 and 5.62 mmol Al kg -1 , and their Ca/Al ratio was 15 mol mol ' contrasting with P. aquilinum from temperate regions where Ca/Al was 1440 mol mol -1 , however the Ca/P was 2 mol mol" 1 in both species. We conclude that P. caudatum behaves as a potassium plant (soluble K/Ca >>1) such as the grass-like families Poaceae and Cyperaceae and accumulates Al in the subterranean organs.
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