Ciclagem biogeoquímica dos nutrientes em uma plantação de Pinus taeda L. no Nordeste Argentino

Abstract

The objectives of this study were to characterize water and nutrient fluxes in a Pinus taeda plantation at 12 year-old located in the northeast of Argentina. The atmospheric deposition and rainfall partitioning into throughfall, stemflow and canopy interception loss and the chemical composition of soil solution in the pinus plantation and in a grassland area was evaluated during a year. Three rain collectors were installed in the grassland area to measure and collect the rainfall (bulk precipitation), twelve rain collectors were installed in the interior of the plantation to measure the throughfall and twelve stemflow collectors (in selected trees) were used to determine the stemflow. To study the chemical composition of the soil solution two sets of tension lysimeters were installed: one in a Pinus taeda plantation and another one in the open area. To collect soil solutions at the depths of 30 and 70 cm sixteen lysimeters were placed in each area. The biomass was quantified and the stock of nutrients in the tree component was estimated, as well as the accumulated litter on the floor and the soil at 1 m of depth. The annual rainfall was 2228 mm, the pine canopy intercepted on average 26,5% and the net precipitation was 73,5%, of which, 68,9 % was by throughfall and 4,6% by stemflow. The anions N-NO3-, SO42- and N-NO2- and the cations Na+ and Ca2+ were the main chemical inputs from bulk precipitation. The transfer of fluxes through the canopy and stems of pine caused an enrichment for most elements mainly potassium and magnesium. The solution of the soil under pine plantation showed a high concentration of ions, mainly base cations (exchangeable), in its composition compared with the grassland area, indicating the importance of nutrient cycling in forest ecosystem. The main budget of nutrients in the pine stand is a non-commercial biomass (needles, branches, roots and litter), showing that depending on the adopted management practices, the output of nutrients may be less than the budget that remains in the site after the forest harvesting.