VA MYCORRHIZAL INFECTION IN RELATION TO EDAPHIC CHARACTERISTICS AND DISTURBANCE REGIME IN 3 LOWLAND PLANT-COMMUNITIES IN THE SOUTH-WESTERN CAPE, SOUTH-AFRICA

1 Levels of infection in the roots of vesicular-arbuscular mycorrhizal (VAM) plants growing in three lowland evergreen shrublands of the Cape Floristic Region, South Africa, were studied and used to assess mycorrhizal activity in these natural ecosystems. 2 Average infection was significantly different between vegetation types. VAM infection levels were lowest in strandveld which has high soil phosphorus contents, intermediate in fynbos (very low phosphorus levels) and highest in renosterveld plants where plant-available phosphorus levels are very low due to competition for the moderately high total phosphorus present in soil. 3 Infection intensity was very variable amongst individual plants, suggesting that mycorrhizal inoculum is patchily distributed in the soil. This is especially marked in fynbos, perhaps as a result of a high proportion of non-mycorrhizal species. 4 In fynbos plants, VAM infection was lower during the first two growing seasons following fire than in older vegetation. Annual plants, which had very low infection levels, were common immediately after the fire but absent from older fynbos vegetation, whilst infection levels were higher in older geophytes and shrubby perennials. Infection levels were unaffected by growth form in strandveld and renosterveld. 5 In the fynbos, there was a significant difference in VAM infection among the more common families. The Scrophulariaceae, although capable of forming mycorrhizas, generally had very low levels of infection whereas some members of the Fabaceae had low levels of infection while others were heavily mycorrhizal. 6 Infection amongst members of the Asteraceae was significantly different between vegetation types indicating that edaphic features had more influence over levels of infection than taxonomic position.