Can C-14-labeled photosynthetic products move between Pinus densiflora seedlings linked by ectomycorrhizal mycelia?

Movement of C-14-labeled photosynthetic products via ectomycorrhizal myceli a linking seedlings of Pinus densiflora is investigated here, a process whi ch may have the potential to be highly ecologically significant. Paired seedlings linked by hyphae of either an unidentified ectomycorrhizal fungus designated T01 or Pisolithus tinctorius were prepared by arranging mycorrhizal and nonmycorrhizal seedlings in an observation rhizobox and all owing mycelial links to form. Shoots of the initially mycorrhizal seedling were photosynthetically labeled with (CO2)-C-14 and movement of C-14 chased by time-course autoradiography. Within 3 d, C-14 was transferred to mycelia and mycorrhizas formed on the u nlabeled seedling, but little C-14 was subsequently transferred to the root s and shoots. The reverse movement of label was also demonstrated. Mycelial fans of T01, with greater hyphal density, accumulated more C-14 than mycel ia of P. tinctorius, whereas higher radioactivity was detected in hyphal st rands than in the mycelial front of P. tinctorius. Ectomycorrhizas and mycelia are strong sinks for photosynthetic products, a nd C transfer can occur bi-directionally in the mycelia. However, as yet no direct evidence indicates any benefit to receiver plants and, thus, supple mentary supply of C to understory individuals may not be ecologically signi ficant.