Mycorrhizal development and growth of inoculated Eucalyptus globulus (Labill.) seedlings in wet and dry conditions in the glasshouse

As Eucalyptus globulus (Labill.) seedlings are being widely outplanted to sites characterised by both high and low rainfall, this study describes the effect of soil moisture availability on mycorrhizal development and growth of seedlings inoculated with three different fungi. The information generated by this study should enable the nurseryman to target which mycorrhizal fungi to select as suitable inoculants for dry and wet sites. Mycorrhizal and non-mycorrhizal seedlings of E. globulus, grown under non-nutrient limiting conditions, were subjected to two different watering regimes from nine weeks after inoculation. During the following eight weeks, weekly measurements of stomatal conductance were made. All fruit bodies were collected, as they were formed, and the plants were harvested at 17 weeks. Of the three fungi used as inoculants, an isolate of Laccaria fraterna (Cooke and Mass.) Peg. formed the highest level of infection on seedlings that were watered normally whereas, on seedlings that were water-stressed, Pisolithus tinctorius (Pers.) Coker and Couch (syn. P. arhizus (Pers.) Raus.) achieved greatest mycorrhizal development. However, this isolate of L. fraterna sustained high levels of infection (>50%) on E. globulus seedlings in both 'wet' and 'dry' regimes. Seedlings subjected to drought conditions possessed significantly less stem and leaf biomass. Although there was a negative correlation between mycorrhizal development and shoot growth on seedlings watered normally, for those raised in the drier regime, benefits attributable to mycorrhizal inoculation were detected. In particular, the stomatal conductances of inoculated plants, raised in the 'dry' regime, were found to be greater than those of non-inoculated plants growing in the same conditions.