Taxas de mineralização de nitrogênio e nitrificação em solos de floresta de várzea no Oeste do Pará

Abstract

Floodplains represent areas of the Amazon that are subject to periodic flooding due to rising water levels in rivers. This “flood pulse” is responsible for changing the dynamics of ecosystems and especially the soil microbiota, impacting biogeochemical cycles. Since nitrogen (N) is directly associated with ecosystem productivity, studies investigating its dynamics in floodplain areas are of paramount importance, since its cycle is dependent on the action of soil microbiota and the discharge from the flood pulse can modify the conditions in the system. Thus, the objective of the present study was to investigate the influence of seasonality of the region on mineralization and nitrification rates in lowland forest soils in western Pará. Twelve soil samples (0-10 cm deep) were collected. in each phase of the hydrograph delimited as a function of the Amazon River flow and the concentrations of ammonium (NH4 +) and nitrate (NO3-) ions in the soil were determined. Mineralization and nitrification rates were determined by the laboratory incubation method for seven days. The results showed that nitrate concentrations were higher than soil ammonium concentrations during the flood and ebb periods. Most mineralization rates were negative, around 58% in flood and 75% in ebb, indicating a probable N immobilization in microbial biomass. The nitrification rates, although not presenting significant differences, were higher in the flood in relation to flood and ebb. It is noteworthy that studies of this order must be carried out over the long term and over a larger area to estimate the contribution of floodplain ecosystems in the Amazon to the nitrogen dynamics in the soil-plant-atmosphere system.