Nitrogen availability in tropical forests of Brazil

Abstract:

Nitrogen availability is considered to be high in tropical forest, especially in relation to temperate forests. However, there is among tropical forest a significant variability in nutrient concentrations and stocks either in soils as well as in the vegetation. Here we review the nitrogen distribution and availability in more than 60 forest sites encompassing different soil types and precipitation regimes of the two main tropical forests biomes of Brazil: the Amazon and the Atlantic Forest. We aimed to determine factors that control nitrogen availability in these forests, using as a proxy of such availability parameters like: foliar and soil nitrogen concentrations, nitrogen stable isotopic composition, and foliar nitrogen:phosphorus ratio. Our main hypothesis is that nitrogen availability will be higher in forest where dry-season precipitation is low and/or weathered old soils prevailed. On the contrary, tropical forests over young soils and/or precipitation is high over the year will have a lower nitrogen availability and will be more phosphorus than nitrogen limited.