It is increasingly evident that in natural plant communities the vegetative mycelia of ectomycorrhizal fungi can form networks of hyphal interconnections which link the root systems of their host plants in both intra-and inter-specific combinations. Root observation chambers have been used to examine the development of these mycelial networks and to assess their functional significance as pathways for the transfer of assimilate between individuals in a range of host-fungus associations. Carbon transfer between plants of Pinus spp. is significantly increased by the presence of mycelial connections and preliminary evidence suggests that such transfer may be enhanced where concentration gradients are induced by shading. The significance of these experimental results is discussed in relation to nutrient cycling processes in natural ecosystems.
SUMMARYUsing perspex observation chambers, the uptake, translocation and distribution of ^ap-labelled phosphorus was studied in ectomycorrhizal mycelial networks of Suillus bovinus (Fr.) O. Kuntze interconnecting plants of Pinus contorta Dougl. ex Loud and Pinus sylvestris L. Label was fed either directly to the cut ends of individual mycelial strands, to plant roots, or to the unsterile peat in the vicinity of advancing mycelial fans. Where ^^V was fed to individual strands or mycelial fans it was taken up and translocated through the mycelium, over distances exceedmg 40 cm, to all host plants connected to the mycelial network. Ectomycorrhizal roots acted as major sinks for phosphate but the label did not move exclusively towards the plant and was distributed throughout the mycelial system. Calculated translocation rates and flux rates suggest that transport is primarily by symplastic flow rather than turgor driven bulk flow. The amount of label accumulated by each plant was signiflcantly related both to the size of the plant shoot and to the number of mycorrhizal root tips but did not appear to be influenced by the transpiration rates of individual plants. Phosphorus supplied directly to plant roots did not move to other plants via the mycelial connections suggesting that movement of phosphorus between the fungus and host is unidirectional.
SUMMARY f !The ability of mycorrhizal (M) and non-mycorrhizal (NM) plants of Pinus contorta (Dougl. ex Loud) to utilize protein as a nitrogen source was examined. Mycorrhizas were synthesized with the fungal symbionts PaxiUus involutus, Rhizopogon roseolus, Suillus bovinus and Pisoiithus tinctorius. The plants were grown under aseptic conditions and provided with nitrogen in the form of either protein or ammonium.Dry weight yields of plants infected with P. involutus, R. roseolus and S. bovinus were significantly higher than those of NM plants when grown on protein as the N source. In these associations yields of M plants on protein were similar to those obtained on ammonium-N. Non-mycorrhizal plants had little ability to use protein N and the same was true of plants infected with P. tinctorius.Plants in those associations which provided a yield increase also contained larger quantities of N. Calculations show that in all tbese cases some of tbe increases of N content arise through utilization of protein.The implications of the results are discussed in relation to the nitrogen nutrition of the plant and to the pattern of N mobilization in soil. It is proposed that the ability of mycorrhizal associations to utilize protein N will lead not only to an increased supply of N to the plant but also to more effective competition with the decomposer population and to an overall tightening of the nitrogen cycle.
SUMMARYThe role of inter-plant hyphal bridges formed by vesicuiar-arbuscuiar (VA) mycorrhizal mycelia was investigated using double pots in which donor plants were grown in the mycorrhizal (M) or non-mycorrhizal (NM) condition with root systems split so that they could be supplied with nutrients in the donor pot. Plantago lanceolata L. and Festuca ovina L. were grown in intraand inter-specific combination as donors and receivers. The normally non-mycorrhizal species Arabis hirsuta L. was included as an additional potential receiver. Nutrient solution or distilled water was applied to the donor pot and the patterns of growth responses, and of nitrogen and phosphorus accumulation were compared in receiver plants with and without mycelial interconnections.Yields of M receivers were significantly higher than those of NM plants in all combinations of plants at the second or third harvest, except in the case of the intra-specific combination of Plantago. A. hirsuta showed no response to nutrient application. Mycorrhizal infection of receivers in the distilled water treatment produced a relatively small response indicating that improved exploitation of sand in the receiver pots was not the cause of growth stimulation m M receivers.Yield increases were associated with higher total N contents of the mycorrhizal receiver plants in three of the species combinations and of P content in all combinations, by the third harvest the gain in P concentration being relatively greater than that of N.The results confirm that VA infection can provide channels for direct inter-plant ""Orient transfer and that transfer is sufficient to sustain significant enhancement of both growth and nutrient composition of receivers, in some cases within six weeks of commencement of the treatment. The probable physiological and ecological significance of these observations is discussed.
SUMMARYPlants of Pimis spp. were grown in observation chambers with the mycorrhizal fungi Suillus hovinus, Pisolithus tinctorius or Paxillus itivohitus. .\hev interconnecting mycelial systems had developed between plants, individual hosts in some chambers of each species were fed with "CO.^. Mycelia from radioactively labelled and unlabelk-d chambers were harvested and their carbohydrates were extracted, separated chromatographically and identified. The major carbobydrates in all of tbe fungi were trehalose, mannitol and arabitol, tbeir relative proportions difFering in the different fungi. The results are discussed in relation both to carbon nutrition of tbe fungus and to carbon transfer between interconnected plants.
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