A ROLE OF VESICULAR-ARBUSCULAR (VA) MYCORRHIZAL FUNGI IN FACILITATING INTERPLANT NITROGEN TRANSFER

Two greenhouse experiments were carried out to study the transfer of nitrogen from berseem (Trifolium alexandrinum) to associated non-legumes via the hyphae of VA mycorrhizal fungi using N-15 as tracer. A special cuvette-membrane system was used to study the effects of restricted and unrestricted hyphal growth between the legume and the non-legume on nitrogen transfer. The roots of berseem plants, either inoculated with the VA mycorrhizal fungus Glomus intraradices or non-inoculated, were separated by a 3 cm root-free zone from the roots of the non-legume. In the first experiment, a split-root technique was employed to label the legume with N-15. Maize was chosen as the non-legume. 50-day old berseem plants were supplied with a N-15-enriched N source, which was added to the outer side of the divided root system of the legume. In the second experiment apple was the non-legume chosen, The legume was labelled with N-15 by injection into the leaf petioles after a 51-day growth of berseem. Both methods of N-15-labelling of the legume were effective in enriching all plant parts with N-15. Transfer of N-15 from berseem to the non-legume infected by the VA mycorrhizal fungus was significantly higher than in the non-infected non-legume over a 28-day period. However, the patterns of N-15 transfer differed between the two experiments. By correcting the value of N-15 in mycorrhizal receiver plants for the background values in the corresponding non-mycorrhizal treatments, 4.7% of the N-15 content of berseem was transferred to apple. In contrast, the amounts of N-15 transferred to mycorrhizal maize were smaller with 0.1% of the N-15 derived from berseem.