The effectiveness of ectomycorrhizal fungi in increasing the growth of Eucalyptus globulus Labill. in relation to root colonization and hyphal development in soil.

Forty-seven different isolates of ectomycorrhizal fungi, from the different genera, were screened for their effectiveness in increasing the growth of Eucalyptus globulin La hi 11. where supply of P is deficient. Plants were grown in a P-delicient sand, in pots, in a temperature- control led glasshouse. Seedlings we re harvested 6-S and K7 d after planting, and were assessed for dry matter production and mywirrhizal colonization. Selected treatments were also assessed for P concentrations in the plant and hyphal development in the soil. Dry weights of inoculated plants ranged from 50 to 350% of the dry Weights of uninoculated plants. Growth increases in response to ectorriycorrhizal inoculation corresponded with increased P uptake by the plant.'Early'colonizing fungal species (Descolea maculata, Hebeloma westraliens, Laccaria laccata and Pisolithus tinctorius) were generally more effective in increasing plant growth than'late'colonizing species (Cortinarius spp. and Hyutenmgium spp.), although there was also variation in effectiveness among isolates of the same fungal species. Plant dry weights were positively correlated (r ² = 0·79-0·84) with the length of colonized root, indicating that fungi which colonized roots extensively were The most effective in increasing plant growth. For some fungi, however, plant growth responses to inoculation were not related to colonized root length. These responses could not.be related to the development of hyphae in soil by the mycorrhizal fungi.