Abstract

SANCHEZ, Belkys; RUIZ, Magaly  and  RIOS, María Magdalena. Materia orgánica y actividad biológica del suelo en relación con la altitud, en la cuenca del río Maracay, estado Aragua. Agronomía Trop. [online]. 2005, vol.55, n.4, pp.507-534. ISSN 0002-192X.

The objective of this research was to study variations in soil organic matter content and composition at different altitudes and their influence on microbial activity and biomass in soils from Maracay River basin (Venezuela). The selected zones are located at: 480 meters above sea level (masl) (savanna with trees); 720 masl (gallery forest) and 1 000 masl (cloud forest). In each zone, a plot was selected, which was divided into three subplots. Ten soil samples were taken from different points in all subplots, at a depth of 0-10 cm. Total organic carbon (TOC), carbon of the humic substances (extracted with alkali), microbial biomass carbon (Cmic, measured by the substrate-induced respiration method), basal respiration (evolution of CO₂), and metabolic quotient were determined. TOC varied between 0.88% and 2.52%. The alkali extracted fraction 529 ranged from 20 to 43% of TOC and was primarily associated with humic acids. Basal respiration values varied between 0.57 and 4.11 μg C-CO₂ g-1 h-1. Cmic ranged from 576 to 1 395 μg Cmic g-1. The highest values of organic carbon, Cmic and basal respiration were observed in the highest zone, whereas the lowest values were observed in the middle zone (P<0.05). Soil organic matter content and composition as well as microbiological activity are influenced by altitude, which is associated with differences in vegetation, temperature, precipitations and soil characteristics.

Keywords : humic substances; organic carbon; microbial biomass; soil respiration; savanna soils; gallery forest; cloud forest.

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