A study of ageing of spruce [Picea sitchensis (Bong.) Carr.] ectomycorrhizas. III. Phosphate absorption and transfer in ageing Picea sitchensis/Tylospora fibrillosa (Burt.) Donk ectomycorrhizas.

Phosphate absorption and transfer to the host was studied in seedlings of Picea sitchensis (Bong.) Carr. ectomycorrhizal with Tylospora fibrillosa (Burt.) Donk grown in Perspex root observation chambers. Phosphate absorption into excised mycorrhizas was reduced in older compared with young mycorrhizas, kinetic analysis indicating physiological differences in phosphate absorption between the two age classes over a range of external concentrations up to 1000μM. Individual young mycorrhizas labelled directly with P transferred more P to the host than older mycorrhizas in the same intact root system. There was variation in the ratio (young:older) suggesting a progressive reduction in nutrient transfer to the host as the mycorrhiza ages. The results are discussed in relation to nutrient accumulation in the field.