Ciclagem de carbono e nutrientes em florestas sazonalmente inundáveis no Pantanal Mato-grossense

Abstract

The soils and vegetation of natural wetlands are disturbed when seasonal flooding occurs. The effects of flooding in these environments are extremely important for the understanding how these forests are organized and how the biogeochemical cycles occur. In this context, the objective of this study was to analyze the carbon and nutrient cycling in two seasonally flooded areas in the northern Pantanal of Mato Grosso. Study sites were located within a protected nature reserve, the Reserva Particular do Patrimônio Natural (RPPN) of the Serviço Social do Comércio (SESC)- Pantanal, with dominant forest stands of Vochysia divergens Pohl (Cambarazal) and Scheelea phalerata (Mart. Ex Sperng.) Burret (Acurizal). In these areas, litter and soil samples were collected for chemical analyzes of carbon, nitrogen, phosphorus, potassium, calcium and magnesium. The litter produced in Cambarazal was larger compared to Acurizal, and its leaves make up the main fraction of the litter. The deposition of this vegetal material in the second semestre, non-flooded period, was double in relation to the period of flood in Cambarazal. There was a correlation between litter deposition and the vapor pressure deficit in air and wind speed. The potential of carbon input and nutrient return in the soil of Cambarazal was higher than Acurizal. However, there was more litter accumulation than decomposition, in both areas, and the decomposition was greater in Acurizal. The release of nutrients through decomposition was higher in Cambarazal considering the amount of litter produced, but in Acurizal the relative release of nutrients was higher. The flooding process resulted in a significant change in total soil carbon, available phosphorus, extractable potassium and aluminum contents. However, total soil nitrogen, calcium and magnesium contents did not change due to flooding. Total soil carbon, available phosphorus, exchangeable potassium and aluminum stocks were higher in Cambarazal, while the soil calcium and magnesium stocks and the fertility, base sum, potential cation exchange and base saturation Higher in the Acurizal, indicating that it is a soil with greater fertility than the Cambarazal. The efflux of CO2 from the soil was higher in the Acurizal and the total carbon contents were higher in the Cambarazal. Therefore, establishing forests in areas of seasonally flooded pastures in the SESC Pantanal RPPN can lead to nutrient concentrations and carbon stock below the forest canopy and the development of "fertility islands".