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 s ites 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 generat ed by this study should enable the nurseryman to target which mycorrhizal f ungi to select as suitable inoculants for dry and wet sites. Mycorrhizal and non-mycorrhizal seedlings of E. globulus, grown under non-n utrient limiting conditions, were subjected to two different watering regim es from nine weeks after inoculation. During the following eight weeks, wee kly measurements of stomatal conductance were made. All fruit bodies were c ollected, as they were formed, and the plants were harvested at 17 weeks. Of the three fungi used as inoculants, an isolate of Laccaria fraterna (Coo ke and Mass.) Peg. formed the highest level of infection on seedlings that were watered normally whereas, on seedlings that were water-stressed, Pisol ithus tinctorius (Pers.) Coker and Couch (syn. P. arhizus (Pers.) Raus.) ac hieved greatest mycorrhizal development. However, this isolate of L. frater na sustained high levels of infection (>50%) on E. globulus seedlings in bo th 'wet' and 'dry' regimes. Seedlings subjected to drought conditions posse ssed significantly less stem and leaf biomass. Although there was a negativ e correlation between mycorrhizal development and shoot growth on seedlings watered normally, for those raised in the drier regime, benefits attributa ble to mycorrhizal inoculation were detected. In particular, the stomatal c onductances of inoculated plants, raised in the 'dry' regime, were found to be greater than those of non-inoculated plants growing in the same conditi ons. (C) 2000 Elsevier Science B.V. All rights reserved.