Plant Ecology 171: 35–52, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 35 Ecophysiology of ectomycorrhizal fungi associated with Pinus spp. in low rainfall areas of Western Australia Tina L. Bell 1,∗ & Mark A. Adams 1,2 1 Forest Science Centre, Water Street, Creswick 3363, Victoria, Australia, 2 Ecosystems Research Group, School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling High- way, Nedlands 6009, Western Australia, Australia; ∗ Author for correspondence (e-mail: tlbell@unimelb.edu.au) Key words: Enzyme activity, Mediterranean-type climate, Plant productivity, Rhizopogon roseolus, Soil health, Soil quality Abstract As a potential means of monitoring functional properties of plantations of Pinus pinaster and Pinus radiata established as part of land rehabilitation in the wheatbelt of Western Australia, we examined aspects of the ecophysiology of ectomycorrhizal fungi associated with tree roots. A single species of ectomycorrhizal fungi, Rhizopogon roseolus, dominated the mycorrhizal flora. Sporocarps of Rhizopogon roseolus appeared with the onset of winter rains in May, increased in number and total biomass to peak in September, and decreased to negligible levels at the beginning of the summer drought in December. A greater number of sporocarps, and consequently a greater biomass of sporocarp tissue, was associated with roots of P. radiata than P. pinaster.A similar seasonal pattern of mycorrhizal root infection was determined by counts of individual ectomycorrhizal root tips from bimonthly collection of soil core samples. At the low rainfall (380 mm annually) site, greater numbers of live root tips were more strongly correlated with soil moisture than organic matter content of soil. In contrast, in wetter areas closer to Perth (800 mm annually), highest numbers of active root tips and greatest amounts of organic matter were both within 0–10 cm depths. Results suggest an overriding importance of soil moisture rather than nutrient status of the soil as the key determinant of spatial and temporal distribution of the fungus. Results from a range of assays determining enzyme activity of soil (protease, phosphomonoesterase, cellulase, L-asparaginase, L-glutaminase and β -glucosidase) surrounding mycorrhizal roots indicated seasonal patterns to be similar to those described for reproductive activity of mycorrhizal fungi. Factors responsible for patterns of seasonal activity and distribution of ectomycorrhizal roots are discussed in terms of managing systems in order to maximise tree growth and form while effectively restoring soil water balance. Introduction Natural hydrological balances of the wheat grow- ing region (wheatbelt) of Western Australia have been disrupted through widespread removal of deep- rooted native perennial vegetation and replacement by shallow-rooted, annual crops that intercept and use a far smaller fraction of annual rainfall and stored groundwater (George et al. 1995; Lambeck 1998; Hat- ton and Nulsen 1999). Deep-rooted trees including Pinus pinaster Ait. and Pinus radiata D. Don are currently being established in low rainfall (<500 mm annually) areas of the wheatbelt as a means of combat- ing rising water tables and associated increases in soil salinity. The successful establishment of plantations on ex-agricultural or cleared land has been targeted as a means to provide a solution to soil water imbalances as well as providing an economic return to farmers (Eastham et al. 1994; George et al. 1995; Bell 1999; Wildy et al. 2000; Lefroy et al. 2001a, b). While a great deal of information relating to above- ground biomass and wood production of P. pinaster, P. radiata and other plantation trees is available, little is known about the contribution of belowground pro- cesses to tree growth. Standard establishment and