FIGURE 3.23 Effect of ectomycorrhizal species diversity on shoot and root growth of birch seedlings when inoculated with a random mixture of mycorrhizal fungal species, selected from a species pool. Data from Baxter and Dighton (2001).

Cairney (1999) discussed the range of ectomycorrhizal species and their varied physiological functions, suggesting that we know relatively little about variation in the physiology of the few fungi that we have studied extensively in the laboratory, let alone the myriad of other species about which we know very little and especially of those fungi that we have yet to encourage to grow in culture. In addition, in their review article,

Cairney and Burke (1996) cite examples of heterogeneity of the function of mycelia of the same ectomycorrhizal fungus as it exploits pockets of different resources in the soil. They suggest that this heterogeneity of function drives both the ability of

Dependent variable Step variable R2 P Total mass NS — —

Shoot mass Diversity 0.129 0.002

Root mass Diversity 0.156 <0.001

Root: shoot Diversity 0.224 <0.001

Growth

Root length Colonization 0.243 <0.001

Total N (mg) NS — —

Total N (mg g−1) Colonization 0.037 0.109

Shoot N (mg) NS — —

Shoot N (mg g−1) Diversity 0.112 0.005

Root N (mg) NS — —

Root N (mg g−1) Diversity 0.037 0.110

Total P (mg) Diversity 0.179 <0.001

Total P (mg g−1) Diversity 0.177 <0.001

Shoot P (mg) Diversity 0.081 0.017

Shoot P (mg g−1) Diversity 0.150 <0.001

Root P (mg) Colonization 0.115 0.004

Nutrients

Root P (mg g−1) Colonization 0.074 0.023

Note: NS=step variable did not meet the 0.15 significance level for incorporation into the model. Source: Data from Baxter and Dighton (2001).