Nutrient status of Amazonian caatinga forests in a seasonally dry area: nutrient fluxes in litter fall and analyses of soils

Amazonian caatinga, a low-stature forest type confined to seasonally waterlogged white-sand soils, occurs at La Esmeralda (Orinoco basin) under a lower rainfall than at San Carlos (Rio Negro basin), where many previous studies have been made. The nutrient status of forest types at La Esmeralda are compared and related to those of forests at San Carlos. At La Esmeralda, stature declines from well-drained palm-rich forest (PRF), via waterlogged tall caatinga (TC), to superficially waterlogged short caatinga (SC). Along this sequence, total fine litter fall decreased (7.6, 6.7, and 5.2 Mg.ha(-1).year(-1)), N flux decreased (66, 59, and 40 kg.ha(-1).year(-1)), Ca flux increased (27, 44, and 85 kg.ha(-1).year(-1)), P flux decreased nonsignificantly, and there was no trend in Mg or K fluxes. Resin-exchangeable P concentrations of 0-10 cm soil samples increased along the sequence (20, 28, and 30 mu g.g(-1)). The conclusion that N is in increasingly short supply as a result of waterlogging agrees with results previously obtained at San Carlos. The P flux in leaf litter fall of forests at La Esmeralda (range 1.0-1.3 kg.ha(-1).year(-1)) is lower than that of tall caatinga at San Carlos (2.0 kg.ha(-1).year(-1)) or ''typical'' rain forests (mean 2.6 kg.ha(-1).year(-1)), suggesting that P is also relatively scarce.