REVIEW

Role of Arbuscular Mycorrhizal Fungi in Biological Nitrogen Fixation and Nitrogen Transfer from Legume to Companion Species

The production of food crops in sustainable agriculture demands the use of renewable resources, which include the potential role of arbuscular mycorrhiza fungi (AMF) and Biological Nitrogen Fixation (BNF) for supplying nitrogen (N) for crops. Associative action of AMF in legumes has a great impact on root, shoot development and phosphorous uptake which results in the enhancement of nodulation and nitrogen fixation. Biological nitrogen fixing crops can contribute N to the neighbouring crops by N transfer. N compounds (NH₄⁺, NO₃^-, amino acids, ureides, peptides and proteins) released from nodulated roots, decomposed legume debris, or root exudates to soil solution are absorbed by AM hyphae as the first direct pathway of N transfer. Absorbed N by AMF is translocated as NH₄⁺, amino acids, and peptides from fungal cell to neighbouring plant cells. This transfer could involve NH₄⁺ and NO₃^- transporters, amino acid permeases and peptide transporters. Plants could be interconnected by mycorrhizal mycelia to form common AM networks that provide the another direct pathways for N transfer from one plant to another. Although the relatively small role of common AM networks in N transfer, the overall AMF contributions to N transfer are considered to be of great importance for legume and non-legume intercropping systems in sustainable agriculture.