The dynamics of ectomycorrhizal infection of Shorea leprosula seedlings in Malaysian rain forests

The development of mycorrhizal infection on seedlings of the dipterocarp, Shorea leprosula (Miq.), was followed for 7 months after germination at three sites in West Malaysia. Arbuscular mycorrhizal infection was not observed. Seedling roots had well-developed ectomycorrhizal sheaths, but no Hartig net, 20 d after germination, i.e. before the leaves had formed. By 2 months a range of ectomycorrhizal types with well-developed Hartig nets were present. Twenty-three types were recognized, of which 15 were common to all three sites, and 20 to two sites. Individual seedlings never had more than five types and normally had one or two types only. The majority of ectomycorrhizas were formed by relatively few fungi and the six most abundant types at each site accounted for 77-92% of the mycorrhizas. On the basis of the frequency of types (i.e. number of seedlings having mycorrhizas of a given type), and the number of times that a type contributed more than 40% of the mycorrhizas on a given seedling it was possible to recognize group of 12 dominant types. At each site new types were encountered at each harvest, and the number of types per harvest also increased. As well as fungi entering the mycorrhizal community as time progressed there was clear evidence that some fungi were lost or declined in relative abundance. Over the study period the level of infection fell at the two sites at which it was initially greatest. Although the community of mycorrhizal fungi was broadly similar at all three sites, overall level of infection, total number of types and number of types per seedling were highest at the site which appeared to have experienced the least disturbance and at which there were the greatest number of adult S. leprosula trees.