Unraveling the ecosystem functions in the Amazonia-Cerrado transition: evidence of hyperdynamic nutrient cycling

The contact between savanna and forest in the Amazonia-Cerrado transition zone is characterized by the hyperdynamics of the vegetation (recruitment vs. mortality). However, the related nutrient dynamics under these conditions are not well understood. We determined for the first time the biogeochemical cycles of the vegetation in the zone of transition estimating the litterfall, nutrient input, decomposition rates, and nutrient release in cerradao and cerrado plots. We examine the hypothesis that nutrient cycling is strongly associated with the vegetation dynamics. The litterfall was sampled in 30 traps placed within 1-ha vegetation plots for 2 years. The release of nutrients from the litterfall back to the soil was also estimated using decomposition bags in the two areas. The decomposition rates did not vary between areas, although in the cerradao the input of total biomass (9.27 Mg ha(-1) year(-1)) and total nutrients (219.17 kg ha(-1) year(-1)), the decomposition of the total biomass, and the cycling of most nutrients through litterfall and decomposition were at least twice higher than in the cerrado. These results confirmed the hypothesis concerning the differences between vegetation types in nutrient cycling, suggesting for the first time that the hyperdynamics observed in both vegetations were also reflected in the biogeochemical cycle, particularly in the cerradao. Thus, it is likely that the rapid and effective cycling of nutrients observed in the cerradao might be a key condition guaranteeing the ability of the cerradao to colonize new areas previously occupied by the typical cerrado.