Seasonal change in phosphorus content of Pinus strobus-Cenococcum geophilum ectomycorrhizae

An important function of the ectomycorrhizal sheath may be the storage and delayed translocation of nutrients to the host. III order to determine whet her there are such phases, we quantified seasonal change in phosphorus cont ent in sheaths of Cenococcum geophilum-Pinus strobus (white pine) ectomycor rhizae. Our held site was a mixed deciduous forest in northern, lower Michi gan. White pine needle and root growth, and density of C. geophilum sclerot ia were determined weekly. Ectomycorrhizae were collected biweekly, as were buried meshes that served to index hyphal growth. Phosphorus content of sh eaths of ectomycorrhizae was measured by energy-dispersive X-rap analysis o f planed, frozen material. From May to Jun 1994, sheath P content declined 0.9%/d. From Jul to Oct sheath P content was low and varied little; C. geop hilum hyphae grew, but needles and roots did not. The fallowing spring from h-lar to May 1995, sheath P content increased 1.2%/d. We suggest, on the b asis of synchrony of changes of sheath P content with fungal and tree growt h, that three seasonal phases of P dynamics in ectomycorrhizal sheaths can be distinguished: (i) uptake in early spring before tree growth, (ii) trans location to tree and fungus during spring, (iii) depletion during summer, f all, and winter when there was only fungal growth. Phosphorus in ectomycorr hizal sheaths may be shared by tree and fungus.