Effects of arbuscular mycorrhizal fungi on the nitrogen distribution in endangered Torreya jackii under nitrogen limitation.

ABSTRACT

MAIN CONCLUSION: Arbuscular mycorrhizal fungi regulated the distribution of nitrogen in the leaves, thereby facilitating the adaptation of the endangered plant Torreya jackii to a low-nitrogen environment. Rhizophagus irregularis was inoculated into sterilized soil to investigate its impact on the distribution ratio of leaf nitrogen in cell wall proteins, cell membrane proteins, water-soluble proteins, and photosynthetic systems which includes the carboxylation system (PC), energy metabolism (PB), and light-harvesting system in the endangered species Torreya jackii. The results showed that R. irregularis reduced the specific leaf weight and the distribution ratio of nitrogen in cell wall proteins in the leaves of T. jackii, whereas it enhanced the distribution ratio of nitrogen in cell membrane proteins and water-soluble proteins. R. irregularis enabled more nitrogen uptake for growth by decreasing the distribution of nitrogen to the structural substances. At low-nitrogen levels, inoculation with R. irregularis improved the plant height (18.78 ~ 36.04%), shoot dry weight (50.53 ~ 64.33%), total dry weight (42.86 ~ 52.82%), maximal net photosynthetic rate (Pmax) (16.83 ~ 20.11%), photosynthetic nitrogen use efficiency (PNUE) (40.01 ~ 43.14%), PC (33.56 ~ 38.59%) and PB (29.08 ~ 34.02%). However, it did not substantially affect the leaf nitrogen content per unit area or the leaf nitrogen content per unit mass. Moreover, Pmax exhibited a significant positive correlation with PC and PB, and all three parameters showed a significant positive correlation with the PNUE, thereby revealing that R. irregularis increased the photosynthetic capacity and PNUE of T. jackii through boosting PC and PB.