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Pteridium caudatum (L.) Maxon Behaves as a Potassium Plant and Accumulates Aluminum in the Subterranean Organs

ABSTRACT 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 that 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−1 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.