Effects of soil phosphorus on spore germination and hyphal growth of arbuscular mycorrhizal fungi.

The direct effects Of soil phosphorus on sport germination and hyphal growth of the arbuscular mycorrhizal fungi (AM), Glomus etunicatum Beck &Beck &Gerd., E3 and Scutellospora heterogama (Nicol &Gerd) Walker &Sanders, were investigated by means of two soil-agar plate experiments. In the first experiment, the percentage spore germination and hyphal length of G. etunicatum, measured at ten different P levels and three periods of incubation, were affected by the P status of the soil. The best correslation with P level in the soil occurred at 7 d of incubation for spore germination and at 14 d far hyphal growth and hyphal growth increment. Spore germination was stimulated when 12.5 μ PO g was applied to the soil and decreased with further soil P increments. Hyphal growth decreased significantly with soil P amendments above 37.5 μg P g In the second experiment including three different P levels and the three AM endophytes, soil P affected spore germination and hyphal growth, and both decreased at the high phosphate treatment for G. etunicatum and S. heterogama. The K3 spare germination was similar to the other two species, but the hyphal growth was poorer. S. heterogama was more sensitive to P fertilization than the Glomus spp. and for the three species the hyphal production was not proportional to spore size.