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

José Frutuoso Do Vale Júnior,Steven Nicodem,Diego Lima De Sousa Cruz,Sandra Catia Pereira Uchôa,Valdinar Ferreira Melo

doi:10.1590/18069657rbcs20140480

José Frutuoso Do Vale Júnior, Steven Nicodem + Show 3 more

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https://doi.org/10.1590/18069657rbcs20140480

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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 Virua 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.

Highlights

The Viruá National Park is situated in the far north of Brazil, in the state of Roraima, with several vegetation physiognomies and complex ecosystems that are specific to the Amazon region, especially the campinarana, characterized by open and scleromorphic shrubby vegetation (3-4 m), low species diversity, and high endemism (Barbosa and Ferreira, 2004)
Soil particle analysis revealed the sandy nature of the soil under non-forest areas (FC1, FC2, arboreal-shrubby campinaranas (ASC), grassy-woody campinaranas (GWC), and pioneer formation (PF)), and silt was the second most abundant fraction (Table 1)
Humin predominates in all the soils studied, especially in the surface, whereas the soluble nature of organic acids, fulvic acid, enable their loss through the soil profile, accumulating humic acid on depth and contributing to formation of spodic horizon from 2 to 3 m deep

Summary

Introduction

The Viruá National Park is situated in the far north of Brazil, in the state of Roraima, with several vegetation physiognomies and complex ecosystems that are specific to the Amazon region, especially the campinarana, characterized by open and scleromorphic shrubby vegetation (3-4 m), low species diversity, and high endemism (Barbosa and Ferreira, 2004). The phytophysiognomical gradations of wooded campinaranas are associated with different levels of soil hydromorphism. The wooded campinarana is replaced by arboreal and shrubby campinaranas, grassy-woody campinarana, and, completely herbaceous vegetation. Hydromorphic soils predominate in the Viruá National Park, largely composed of Spodosol and Quartzipsamment. The Spodosol are predominant in all types of campinaranas (from wooded to grassy-woody). In Quartzipsamment, the predominant vegetation is open and of small size. There are inselbergs and forest and mountain landscapes. In contrast to the campinarana soils, some of the Oxisol, Inceptisol, and Plinthic Acrudox soils under forest areas are more clayey and were formed from acidic rocks and gneiss (Mendonça et al, 2013)

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