Root biomass, depth distribution and relations with leaf biomass of Colophospermum mopane

Abstract

On an area covered by dense stands of Colophospermum mopane with little or no grass cover, ten sites were randomly selected. In the centre of each site, a core (monolith) of soil (2.0 m × 0.5 m × 1.0 m deep) was excavated and removed in 5 layers of 200 mm. Roots were washed from the soil and sorted into classes (0–1.0 mm, > 1.0–5.0 mm, > 5.0–10.0 mm, > 10.0 mm), dried and weighed. The canopy dimensions of C. mopane around each excavation were measured and the leaf dry mass estimated using a regression equation which relates spatial canopy volume to leaf dry mass. Total root biomass ranged from 9 760 kg ha− 1 to 29 790 kg ha− 1 (mean: 17 354 kg ha− 1). Of these a mean of 19% were in the 0–1.0 mm diameter class, and 20.3%, 16.2% and 44.5% in the > 1.0–5.0 mm, > 5.0–10.0 mm and > 10 mm diameter classes respectively. A mean of 66.1% of all fine roots (< 5.0 mm) was found within the first 400 mm of the soil. The coarse roots (> 5.0 mm) were virtually absent within the 0–200 mm soil layer, with the highest concentration between 200–600 mm. Leaf biomass was found to be significantly lower than the root biomass.