A role of vesicular-arbuscular (VA) mycorrhizal fungi in facilitating interplant nitrogen transfer

Abstract

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 15N 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 15N. Maize was chosen as the non-legume. 50-day old berseem plants were supplied with a 15N-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 15N by injection into the leaf petioles after a 51-day growth of berseem. Both methods of 15N-labelling of the legume were effective in enriching all plant parts with 15N. Transfer of 15N 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 15N transfer differed between the two experiments. By correcting the value of 15N in mycorrhizal receiver plants for the background values in the corresponding non-mycorrhizal treatments, 4.7% of the 15N content of berseem was transferred to apple. In contrast, the amounts of 15N transferred to mycorrhizal maize were smaller with 0.1% of the 15N derived from berseem.