Ectomycorrhizas as nutrient absorbing organs.

Early work on ectomycorrhizas indicated that they were probably adapted to efficient nutrient absorption. The use of excised mycorrhizas has allowed study of their properties as absorbing organs. The factors affecting their rates of nutrient uptake are similar to those of other absorbing organs but their rates are often greater. On absorption the nutrient is primarily accumulated in the fungal layer but may be mobilized later by reactions under metabolic control. Phosphate is accumulated in particularly large quantities as polyphosphate, which probably explains the linear relations of phosphate absorption and oxygen uptake in certain conditions. Hyphal connections between the fungal sheath and the substrate are variable, and this poses problems about absorption of ions of low mobility, and about the function of surface phosphatases. The fungal sheath is dependent on the host for carbohydrate and the drain on it may be considerable.