Net NH4+ and NO3- fluxes, and expression of NH4+ and NO3- transporter genes in roots of Populus simonii after acclimation to moderate salinity

Key message Net NH (4) (+) flux was higher in fine roots of P. simonii after NaCl treatment compared to the NO (3) (-) flux which was consistent with the expression levels of AMTs and NRTs. The characteristics of nitrogen uptake under salt stress would provide insights into the mechanisms of salt tolerance in plants. In the present study, net NH4 (+) and NO3 (-) fluxes were measured using the non-invasive micro-test technique, and transcript abundance of ammonium/nitrate transporter genes (AMTs/NRTs) were determined by real time PCR in the fine roots of Populus simonii after treatment for 21 days with 75 mM NaCl. The NH4 (+) and NO3 (-) fluxes showed heterogeneous spatial patterns along the root tip in nutrient solution. The maximum influx of NH4 (+) occurred near the root tip, while that of NO3 (-) was 15 mm from the root tip. The net NO3 (-) flux was inhibited by ca. 25 % with the provision of NH4 (+). On average, the newly grown fine roots took up more NH4 (+) after the 75 mM NaCl treatment than did the control. Consistent with the NH4 (+) and NO3 (-) influxes, most AMTs were up-regulated in the salt-treated roots relative to the control, while most NRTs were down-regulated. Our study provides insights into nitrogen uptake and the AMT/NRT expression levels in the fine roots of P. simonii after acclimation to moderate salinity. This may be valuable for understanding nitrogen uptake mechanisms after adaptation to salinity.