AM fungi modulate organic nitrogen preference of Eucalyptus to enhance seedling growth under low fertilization

The results indicated that the height, ground diameter and crown width of <i>Eucalyptus</i> seedlings under 2.5 mM glycine and 0.3 mM Pi (G2P2) treatment were 3.23, 0.82 and 3.70 times higher than those without organic nitrogen under 0.03 mM Pi (N0P1) treatment, respectively. Inoculation with AM fungi contributed 10.85%-162.00% increase in dry weight compared to non-mycorrhizal (NM) treatments. Mycorrhizal seedlings also showed significantly higher total phosphorus contents, nitrogen use efficiency and activity of glutamine synthetase, relative to NM treatments. The relative expressions of genes related to organic nitrogen transport (<i>EgAAP3</i>, <i>EgLHT1</i>, <i>EgProt2</i>) and nitrate nitrogen transport (<i>EgNPF4.5</i>, <i>EgNPF6.3</i>, <i>EgNPF8.1</i>) were up-regulated in mycorrhizal <i>Eucalyptus</i> roots, compared to the NM treatment. Non-mycorrhizal <i>Eucalyptus</i> favored peptone, while mycorrhizal <i>Eucalyptus</i> preferred glycine. <i>Eucalyptus</i> growth under 2.5 mM organic nitrogen and 0.3 mM Pi (N2P2) treatments were promoted markedly, regardless of organic nitrogen source. Whereas, the growth of mycorrhizal <i>Eucalyptus</i> under 0.25 mM organic nitrogen and 0.3 mM Pi (N1P2) treatments were increased the most. This study explored the organic nitrogen and AM fungi fertilizer mode for <i>Eucalyptus</i>, this has potential to improve production practice of <i>Eucalyptus</i> under low nitrogen and phosphorus condition.