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Root penetration rate was estimated for the liana Davilla kunthii St. Hill (Dilleniaceae) in a secondary forest in eastern Amazonia by relating aboveground growth with root depth measurements. Basal diameter, height, number of leaves and number of scars of approximately 100 individuals were monitored between 1991 and 1996. These measurements were used to estimate the age of 28 seedlings (up to 137 cm, of height) that were excavated for root depth measurements, and a model was derived for estimating root penetration rate for D. kunthii at this site. The deepest individual excavated had roots as deep as 10 m and had a mean estimated age of 15 years. Root penetration rate was higher below 3 m depth than in more superficial soil, perhaps due to a decrease in soil resistance, with depth. Some individuals made use of less resistant soil, such as leaf-cutter ants\' nests or the channels of dead roots, to increase their root depth. Pre-dawn leaf water potential, measured in 28 other individuals, was uniformly high in plants with a diameter greater than 12 mm, but highly variable in plants with a smaller diameter, indicating lower water deficit in more deeply rooting plants. Deep rooting was shown to be a priority in the development of D. kunthii and may contribute to its success in establishing in regenerating seasonal forests. Soil heterogeneity plays an important role in allowing for deeper root penetration, which may result in a reduction in the water deficit during the dry season. (C) 2003 Elsevier B.V. All rights reserved.

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