RELATIONSHIPS BETWEEN SEED RESERVES, SEEDLING GROWTH AND MYCORRHIZAL RESPONSES IN 14 RELATED SHRUBS (ROSIDAE) FROM A LOW-NUTRIENT ENVIRONMENT

1. The influence of seed reserves on seedling growth and phosphorus acquisition of 14 vesicular-arbuscular mycorrhizal (VAM) shrub species belonging to the Rosidae and indigenous to the flora of the nutrient-poor soils of the Cape Fynbos, South Africa, was studied in the presence or absence of mycorrhizal inoculum. 2. It is expected that among potentially VAM plant species found in a low-nutrient, high-light environment those with small seed reserves will have a higher dependency on mycorrhizas for seedling establishment than larger-seeded species. 3. Growth of the seedlings when non-mycorrhizal was strongly controlled by seed reserves. Most non-mycorrhizal plants were unable to acquire soil phosphorus unless they possessed alternative nutrient-acquiring root modifications. 4. Mycorrhizal responses in terms of mass and phosphorus content of inoculated plants compared to uninoculated plants are negatively correlated with the logarithm of seed mass and phosphorus content. Thus, it is suggested that seed size among the Rosidae in a low-nutrient environment is a trade-off between dispersal distances and the ability to establish a competitive presence in the absence of mycorrhizal inoculum, with no single seed size conferring an absolute advantage to VAM plant species. 5. The simultaneous evolution of cluster roots and large seeds in low-nutrient environments is proposed as a mechanism allowing for the adoption of the non-mycorrhizal state in some members of the Rosidae.