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

Forty-se\'en different isolates of ectomycorrhizal fungi, from 16 different genera, were screened for their etfecti\eness in increasmg the growth of Eucalyptus globulus Labill. where supply of P is deficient. Plants were grown in a P-deficienI sand, in pots, in a temperature-controlled glasshouse. Seedlings were harvested 63 and 87 d after planting, and were assessed for dry matter production and mycorrhizal colonization. Selected treatments were also assessed for P concentrations in the plant and hyphal de\elopment in the soil. Dry weights of inoculated plants ranged from 50 to 350",, of the dr>' weights of uninoculated plants. Growth increases in response to ectomycorrhizal inoculation eorresponded with increased P uptake by the plant. 'Early' colonizing fungal species (Descolea macutata, Hebetoma westraliense. Laicaria laccata and Pisolithus linclorius) were generally more effecti\'e in increasing plant growth than 'late' colonizing species (Cortinarius spp. and Hysterongium spp.), although there was also variation in effectixeness among isolates of the same fungal species. Plant dry weights were positively correlated (r= 079-0-84) with the length of colonized root, indicating that fungi which colonized roots extensiveiy were the most effective in increasing pSant 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 mycorrbizal fungi.