VESICULAR-ARBUSCULAR MYCORRHIZA IN NATURAL VEGETATION SYSTEMS: IV. TRANSFER OF NUTRIENTS IN INTER- AND INTRA-SPECIFIC...

The role of inter-plant hyphal bridges formed by vesicular-arbuscular (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 intra-and 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 in 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 nutrient 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.