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Loblolly pine (Pinus taeda L.) seedlings were grown axenically in mycorrhizae synthesis cultures with either the symbiont Pisolithus tinctorius (Pers.) Coker and Couch or Thelephora terrestris (Ehrh.) Fr. Glassware was designed to allow synthesis of mycorrhizae on two seedlings physically separated except for a bridge formed between the two root systems by mycorrhizal fungus mycelium. Glucose—C14 and sucrose—C14 were used as tracers to investigate movement of labeled compounds from mycorrhizal roots to external mycelium, from external mycelium to roots and from one root system to the other via shared mycelium. Whether applied to foliage as glucose—C14 or sucrose—C14, C14 was readily translocated to pine roots. Transport of C14 from mycorrhizal roots to external hyphae of T. terrestris up to a distance of 12 cm was shown, but only slight movement of C14 occurred into external hyphae of P. tinctorius. The introduction of glucose—C14 and sucrose—C14 to isolated strands of T. terrestris resulted in the movement of C14 from strands to roots. Movement of isotope from one seedling to the other via mutually—shared mycelium did not occur in the synthesis cultures; however, C14 movement between root systems artifically linked by mycelial strands indicated that interplant exchange can take place. Evidence suggests that mycorrhizal fungi such as T. terrestris could be effective in the exchange of organic and possibly other materials between root systems in an ecosystem.

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The extent and rate of interspecific translocation of P—32 and Ca—45 were determined when radiosotopes introduced into stumps of seven red maples were found in leaves of 19 other species which were up to 24 ft from the donor maples. The mode of interspecific transfer may be either by exudation from the donor and absorption by the acceptor species or through mutually shared mycorrhizal fungi. Root grafting probably is not important in transfer. The importance of recognizing the root mass of an ecosystem as a functional unit, rather than an association of independent entities, is emphasized.