Growth effects of the vesicular-arbuscular mycorrhizal fungus Glomus constrictum on maize plants in pot trials

Maize plants were inoculated with Glomus constrictum in soil of low phosphorus content amended with five rates of P in the form of Ca-3(PO4)(2). Maize dry matter yield was increased by addition of P up to 30 and/or 60 mg P/kg soil, above that it began to decrease to reach at 100 mg P/kg a value similar to that of the control. At all P levels used, the shoot and root (total plant) dry mass of inoculated plants was significantly increased compared with the non-inoculated controls and this increment ranged in some cases between 50 and 70 %. Development of vesicular-arbuscular mycorrhizal fungus (VAM) monitored in terms of P contents in dry matter of maize revealed that the P content of plants not inoculated with G. constrictum was not influenced by P addition to soil. On the other hand, P content of maize plants inoculated with VAM was dramatically increased by increasing P levels of soil and was maximum at 30 mg P; above that it began to decline. Mycorrhizal root infection (expressed as percentage of root length infected) increased by increasing the P concentrations above the soil basal level up to 80 mg P where the infected root length was 72 % of the total root length after 28 d of planting. The increase in VAM spore formation in soil was similar to that of root infection except that the highest spore number was sieved from soil at 60 mg P/kg soil.