Characterization of Organic Matter under Different Pedoenvironments in the Viruá National Park, in Northern Amazon

Abstract

Soil organic matter (SOM) fractions result from a variety of environmental processes, which affect incorporation and production rates, decomposition, alteration, and/or mineralization of organic matter. The aim of this study was to characterize SOM under the environments of rain forest, wooded campinarana (grasslands), arboreal-shrubby campinarana, grassy-woody campinarana, and pioneer plants of the Viruá National Park, in the north of the Brazilian Amazon. After chemical and physical characterization and soil classification, total organic carbon (TOC), total N, microbial activity, organic C from fulvic acid fractions (FA), humic acid (HA), and humin (Hu) were determined at two depths (0.00-0.15 and 0.15-0.30 m). The TOC was lower in the grassy-woody campinarana, arboreal-shrubby campinarana, and pioneer formation areas than in the rain forest. Higher values of microbial activity were related to forest ecosystems in soils without physical or water restrictions and with better fertility compared to the other areas. The Hu predominated in all vegetation types studied, especially in the surface layer, because of the more soluble nature of HA and FA; and the higher values of HA/FA ratios in wooded campinaranas indicate that these environments contribute to higher losses of humic substances through fulvic acid forms, due to better drainage conditions.

The influence of late Quaternary sedimentation on vegetation in an Amazonian lowland megafan

“…The expansion of a few pioneer, white‐sand specialist trees over the sand dunes may have facilitated the establishment of generalist tree species originated from the surrounding forests, with the most important environmental modifications possibly being the incremental soil organic matter, tree root stabilization, and the emergence of understory individuals with mild microclimatic requirements. Both inside Viruá megafan and elsewhere soils underlying Amazonian white‐sand forests have higher contents of organic matter than adjacent grassland/shrubland soils (Barbosa and Ferreira, ; Mendonça et al ., ; Feitosa et al ., ; Vale Junior et al ., ). Concentrations of K, P and the sum of bases were also higher in white‐sand forest soils than grasslands, which may be related to the organic matter cycling (Mendonça et al ., ; Feitosa et al ., ).…”