Efeito da umidade do solo nas características da vegetação sob diferentes períodos sazonais em uma floresta de terra firme na Amazônia Central

Abstract

The international scientific community has been focusing on the occurrence of more intense extreme events over a shorter period of time, such as storms and prolonged droughts. The Amazon rainforest, in turn, has become an important object of study due to its important role in the exchange of CO2 and H2O with the atmosphere. In this sense, the relationship between soil moisture and the production of above-ground biomass (litter and tree diameter increment) is of fundamental importance for the parameterization of current climate models. The aim of this study was to relate soil moisture at different depths to litter production and tree diameter increment over a one-year period (December 2020 to November 2021) in the Central Amazon. The study area is located on a plateau within the boundaries of INPA's Tropical Silviculture Experimental Station (E.E.S.T). Soil moisture values were obtained using sensors located in a deep well with positions varying between 0.025 and 15 m from the surface. The litter was quantified using suspended collectors measuring 0.5 x 0.5 x 1 m in height (0.25 m² of collection area). The litter was collected on the 15th and 30th of each month for a period of one year, and the fractions collected were separated into leaves, branches and reproductive material. In the laboratory, the material was dried in an oven at 65°C±2°C for 72 hours or until it reached a constant weight. The increase in diameter of the trees located adjacent to the litter collectors was obtained by measuring monthly dendrometric bands installed in 67 individuals. Rainfall data was also collected using a rain gauge installed in the study area. Pearson's correlation (r) between monthly soil moisture values and the variables diameter increase and rainfall was calculated using Bonferroni's probability. For the period covered by this study, total annual litter production was 8.81 ± 0.11 Mg.ha-1.year-1 (CI=95%), with peak production occurring in September (1.21± 0.11 Mg.ha-1.year-1) with a correlation coefficient with rainfall of r= -0.70 (p<0.05). Leaf fall contributed 76.62% of the total annual litterfall, followed by branches (13.84%) and reproductive material (4.86%). It is unlikely that the increase in diameter is influenced by regional rainfall, with only a weak relationship between these two variables (r= 0.37; p= 0.23). The correlation between monthly soil moisture and litter was generally weak in the superficial soil layers, but varied significantly in the deeper layers. When only the leaf and twig litter fractions were analyzed, they were negatively correlated with soil moisture at higher depths. Reproductive material showed a positive relationship with soil moisture, with its highest production when there is a higher water content in the soil. The increase in tree diameter and soil moisture showed weak correlations at most depths, with negative correlations in the upper layers and positive correlations in the deeper layers. It can be concluded that soil moisture in the more superficial layers shows a high degree of variation when compared to the environmental and diameter increment variables, resulting in weaker relationships for the study period. The average monthly increment was higher when there was a higher water content in the soil at different depths. Total litter production decreased when there was an increase in soil moisture at greater depths.