WATER STRESS IN THE AMAZON FOREST CHANGES THE DISTRIBUTION AND CONTENT OF AGGREGATES AND THE STOCK OF C E NUTRIENTS IN THE SOIL

Abstract

Resource manipulation research is an essential tool for understanding the impact of ecosystem changes brought about by extreme events, such as a prolonged drought in a humid environment. The objective was to evaluate the C stock and nutrients in the soil, and the mass and C and N contents of humid tropical forest soil aggregates under 14 years of induced drought in a long - term experiment (ESECAFLOR) in the Caxiuanã National Forest, eastern Amazonia. The study was conducted in plots called A (control) and B (exclusion of approximately 50% of rainfall continuously since 2001), each with 1 ha. Soil samples were collected in three layers (0.0-0.1, 0.1-0.2, 0.2-0.3 m) in March 2015, in four points (n = 4) using dutch auger (nutrients), cylindrical ring sampler (density) and trench for removal of monoliths of 1 dm³ for aggregates. The values of C, N, P, Ca, Mg and K, soil density, mass of aggregates of the following diameter classes (> 4; 4-2; 2-1; 1-0.25; 0.25-0.053 and <0.053 mm) and the C and N contents in each class of aggregates were determined. The data were submitted to analysis of variance and the means were compared by t test (C and nutrients stocks) and Tukey test (mass and C and N contents of the aggregates). There was difference in the density and nutrient stock between the plots. The C stock was higher in the Plot A and P, K and Mg were higher in Plot B in all layers evaluated. Plot A presented larger masses of macroaggregates, and in both plots there was a higher content of C and N in the microaggregates. Drought induced in the forest affected soil aggregation and dynamics of C and nutrients.