The ecology of ectomycorrhiza formation and functioning

Factors in inoculum potential/infection levels/plant growth response are analysed and experimental approaches to propagule germination, growth through soil and rhizosphere growth are indicated. It is suggested that seedling rhizosphere germination of basidiospores occurs particularly with early stage fungi, while late stage fungi may be advantaged by germination/growth on exudates from older parts of roots or on litter (and its associated microorganisms) and their tolerance of antimicrobial substances in litter. Relative growth in the rhizosphere is likely to dominate the mycorrhizal species composition and this may be a good selection method for organisms tolerant of stress and pollution conditions. As mycorrhizal function in nutrient uptake is largely determined by fungus growth into soil, there is need for much more experimental study of factors affecting this, and of the potential photosynthate drain this could represent. The possibility of selection/breeding mycorrhizal fungi with both ‘early stage’ and ‘late stage’ attributes is raised.