FACTORS AFFECTING THE SPREAD OF VESICULAR MYCORRHIZAL FUNGI IN SOIL.

The effect of root density on the spread of vesicular-arbuscular mycorrhizal infection was measured using Trifolium repens (clover) and Festuca rubra (fescue). Seeds of both host species were sown in large troughs at three different distances apart, which resulted in different root densities that persisted for up to 15 weeks. For clover, colonization (i.e. total length of infected root) and linear spread were favoured by greater root densities, and at the greatest root density colonization seemed to proceed faster than root extension. In fescue, root density was positively related to linear spread up to about 23 cm root cm-3 soil, but greater root density was supraoptimal for linear spread but not for colonization. Although root density had important effects on the spread of infection, effects of plant species were much greater. Fescue had more total root (five times that of clover), but it supported less linear spread and less than half the total length of infected root. [ABSTRACT FROM AUTHOR]