The growth response of potato to infection by vesicular-arbuscular mycorrhizal fungi (VAM) (Glomus dimorphicum, G. intraradices, and G. mosseae), at increasing levels of soil phosphorus (P), was related to VAM-altered mineral status of the plant. In addition, the morphological development of the VAM was characterized using light and scanning electron microscopy.
Four weeks after inoculation, arbuscules and coiled hyphae were the predominate fungal structures within the roots, however, vesicle development increased steadily over the remainder of the 12 week growth period. As expected, the percent infection of roots by VAM decreased with increasing soil-P level. Leaf area, relative growth rate (RGR), lateral branching and root dry weight were increased by VAM, although the relative-response diminished with increasing soil-P level. A similar response to VAM-infection was evident for the concentration of and total shoot N, P and K. Examination of the shoot N status indicated that VAM influenced the rates at which the plant was partitioning N into various N pools. But again, differences between non-VAM and VAM plants tended to decrease with increasing soil-P level. These results indicate that VAM modification of dry matter accumulation and nutrient uptake is mostly a consequence of the alleviation of P-deficiency of the plant and the improved growth of roots, allowing increased mineral absorption.