Effects of water supply and soil type on growth, vessel diameter and vessel frequency in seedlings of three fynbos shrubs and two forest trees.

Received 17 December 1998; revised 17 September 1999The principle aim of this paper is to ascertain the relationship between plant biomass, vessel size and vessel frequency in relation to soil type and available water. Inherent within this primary determinant is an attempt to provide information on the mechanisms attributing to the high species diversity within the Fynbos Biome and the forces controlling the boundaries between communities. To achieve this objective two treatments tested fynbos and forest plants for the effects of available water and nutrients on xylem vessel morphology and plant biomass. In the watering treatment mean vessel diameters and vessel frequencies for Protea nitida and Cunonia capensis do not significantly differ between the wet and dry treatments. This suggests that neither Protea nitida nor Cunonia capensis are able to adapt vessel morphology to changes in available water. The results for the nutrient treatment show that for the two Protea species Protea neriifolia and Protea nitida there is no significant difference in vessel diameters and frequencies between the two soil types. These results suggest that fynbos and forest species are probably genetically adapted to the environments in which they live, as a result of which vessel morphology of these woody species lack the plasticity to adapt to changes in soil type and soil moisture. We propose that this is because soil type and water availability play important roles in maintaining boundaries between plant communities in the fynbos.Keywords: Fynbos, soil moisture, soil nutrients, vessel frequency, vessel diameter, Protea neriifolia, Protea repens, Protea nitida, Kiggelaria africana, Cunonia capensis. [ABSTRACT FROM AUTHOR]