THE DYNAMICS OF ECTOMYCORRHIZAL INFECTION OF SHOREA-LEPROSULA SEEDLINGS IN MALAYSIAN RAIN-FORESTS

The development of mycorrhizal infection on seedlings of the dipteroca rp, Shorea leprosula (Miq.), was followed for 7 months after germinati on at three sites in West Malaysia. Arbuscular mycorrhizal infection w as not observed. Seedling roots had well-developed ectomycorrhizal she aths, but no Hartig net, 20 d after germination, i.e. before the leave s had formed. By 2 months a range of ectomycorrhizal types with well-d eveloped Hartig nets were present. Twenty-three types were recognized, of which 15 were common to all three sites, and 20 to two sites. Indi vidual seedlings never had more than five types and normally had one o r two types only. The majority of ectomycorrhizas were formed by relat ively 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 th e number of times that a type contributed more than 40% of the mycorrh izas on a given seedling it was possible to recognize group of 12 domi nant types. At each site new types were encountered at each harvest, a nd the number of types per harvest also increased. As well as fungi en tering the mycorrhizal community as time progressed there was clear ev idence that some fungi were lost or declined in relative abundance. Ov er the study period the level of infection fell at the two sites at wh ich it was initially greatest. Although the community of mycorrhizal f ungi was broadly similar at all three sites, overall level of infectio n, 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 tree s.