Effects of environmental variables on vesicular-arbuscular mycorrhizal abundance in wild populations of Vangueria infausta

Vesicular-arbuscular endomycorrhizal fungi include among its members some of the most widespread root symbiont species. It is not known whether these fungal species show environmental or host preferences. In 13 semi-arid savanna sites in Botswana, we found positive correlations between individual environmental factors and the abundance of VAM associations in the roots of an important host, the indigenous fruit tree Vangueria infausta (Rubiaceae). The concentration of phosphorus in the leaves of the host was positively correlated with both phosphorus in the soil and the abundance of VAM associations in its roots, indicating direct benefits to the host of this association. Abundance of VAM associations was significantly different between the studied sites and between seasons and was positively correlated with the mean annual rainfall. In addition, there was a negative correlation with phosphorus concentration in the soil. The differences between the summer and winter abundance of VAM associations were positively correlated with the density of bush cover and the amount of grazing. The apparent correlation found between the abundance of VAM in V. infausta and bush and tree community composition is presumably related to correlations between these two parameters and environmental conditions.