THE EFFECT OF PHOSPHORUS ON THE MYCORRHIZ AL COLONIZATION OF MAIZE BYGLOMUS-MOSSEAE (NICOL. GERD)

The effect of vesicular-arbuscular (VA) endomycorrhizae on plant growt h and P uptake was studied at different rates of phosphorus phosphorus amendment and different soil volumes under greenhouse conditions. Mai ze plants (Zea mays L. cv. Pioneer) were grown for six weeks in a pot experiment using calcareous sandy soil and three phosphorus rates (0, 50, 250 mg P kg(-1) soil, marked P0, P1, P2) ranging from deficient to supraoptimal for the plant. The soils were either inoculated with VA endomycorrhizal fungi (MO+VA), or the plants were raised without VA in oculation (MO-VA). Different volumes of soil available to the plants w ere created by using pots with different volumes (0.5. 2.0, 5.0 and 10 litres). The positive effect of mycorrhizal inoculation on the shoot growth declined as phosphorus fertilization was increased. For the var ious soil volumes, the effect of mycorrhizal inoculation on the shoot mass rose as the soil volume increased. In all cases, mycorrhizal plan ts had higher P contents. The positive effect of mycorrhizal inoculati on on plant phosphorus uptake was exhibited even when phosphorus was a pplied. Phosphorus fertilization reduced the degree of root colonizati on and also the quantity of external hyphae. The results suggest that mycorrhizal inoculation had different effects depending on the pot vol umes, thus explaining the differences between results obtained in fiel d and pot experiments.