Florestas secundárias na Amazônia Central: nutrientes foliares de três espécies pioneiras e do solo sob sua influência

Abstract

Subsistence agriculture and cattle ranching are common land use practices in the Amazon. Since changes in land use affect biogeochemical cycles, the secondary forests that grow after abandonment of such practices develop at varying speeds, due, in part, to changes in nutrient dynamics. In order to understand nutrient dynamics in regenerating forests, as well as the importance of pioneer species in this process, we measured the concentration of macronutrients in the leaves of Vismia cayennensis, Cecropia sciadophylla, and Bellucia imperialis. We also measured macronutrients in the soil of regenerating forests around those trees. Measurements were taken in secondary forests at different stages of regeneration. We found that prior land use, time since abandonment, and number of fire events had a relatively weak relationship with the concentrations of leaf and soil macronutrients, explaining between 10 and 38% of the variation in macronutrient concentration. Despite the weak overal relationship, the observed patterns suggest that: a) management practices affect the processes involved in N cycling and availability of N, b) in V. cayennensis the management practices are altering the resorption of nutrients prior to leaf abscission and senescence and c) it is likely that Ca is becoming limiting in secondary forests as its concentration decreases with the age of the stand. C. sciadophylla had the highest P, K and Mg resorption efficiency as well as the highest leaf nutritional value, measured by C:N ratio. Among the three pioneer species, therefore, C. sciadophylla has the highest potential for natural regeneration of abandoned lands.