MYCORRHIZAL FUNGUS PROPAGULES IN THE JARRAH FOREST .2. SPATIAL VARIABILITY IN INOCULUM LEVELS

Spatial variations in the capacity of propagules of arbuscular mycorrh izal (AM) and ectomycorrhizal (ECM) fungi to form associations in thei r natural habitats were investigated using bioassays with bait plants grown in intact cores of forest soil. These cores were collected from a sclerophyllous forest community dominated by Eucalyptus marginata Do nn ex Smith (jarrah) and E. calophylla Lindley (marri) trees with a di verse shrub understorey in the mediterranean (winter rainfall) climati c zone of Western Australia. Small-scale (adjacent core) variations in the capacity of AM fungi to form associations were found to be as sub stantial as differences between locations 15 m apart. Comparisons of A M fungus colonization patterns within the roots of seedlings growing i n the same core indicated that there was considerable spatial heteroge neity in the inoculum potential of 'individual' fungi within these 11 volumes of soil. A second experiment included bait plants to measure E CM formation as well as AM formation and also considered the impact of soil disturbance. The disruption of hyphal networks reduced mycorrhiz al formation somewhat, but it still remained highly variable. Some of this spatial heterogeneity could be attributed to differences in the o rganic matter content, length of fungal hyphae, or length of old mycor rhizal roots, measured within soil cores. In jarrah forest soil, mycel ial systems of AM and ECM fungi apparently were localized in separate domains, and there were also zones where non-mycorrhizal roots (mostly cluster roots produced by members of the Proteaceae) predominated. Mo re research is required to determine the size of domains of mycorrhiza l mycelial systems in soils, how these spatial patterns change with ti me, and if they are associated with zones of resource utilization by d ifferent 'functional groups' of roots.