AUTHOR=Wu Fei , Fang Fengru , Wu Na , Li Li , Tang Ming TITLE=Nitrate Transporter Gene Expression and Kinetics of Nitrate Uptake by Populus × canadensis ‘Neva’ in Relation to Arbuscular Mycorrhizal Fungi and Nitrogen Availability JOURNAL=Frontiers in Microbiology VOLUME=11 YEAR=2020 URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00176 DOI=10.3389/fmicb.2020.00176 ISSN=1664-302X ABSTRACT=

Plants and other organisms in the ecosystem compete for the limited nitrogen (N) in the soil. Formation of a symbiotic relationship with arbuscular mycorrhizal fungi (AMF) may influence plant competitiveness for N. However, the effects of AMF on plant nitrate (NO3–) uptake capacity remain unknown. In this study, a pot experiment was conducted to investigate the effects of N application and Rhizophagus irregularis inoculation on the root absorbing area, uptake kinetics of NO3–, and the expression of NO3– transporter (NRT) genes in Populus × canadensis ‘Neva’. The results showed that R. irregularis colonized more than 70% of the roots of the poplar and increased root active absorbing area/total absorbing area. The uptake kinetics of NO3– by poplar fitted the Michaelis–Menten equation. Mycorrhizal plants had a higher maximum uptake rate (Vmax) value than non-mycorrhizal plants, indicating that R. irregularis enhanced the NO3– uptake capacity of poplar. The expression of NRTs in roots, namely, NRT1;2, NRT2;4B, NRT2;4C, NRT3;1A, NRT3;1B, and NRT3;1C, was decreased by R. irregularis under conditions of 0 and 1 mM NH4NO3. This study demonstrated that the improved NO3– uptake capacity by R. irregularis was not achieved by up-regulating the expression of NRTs in roots. The mycorrhizal pathway might repress root direct pathway in the NO3– uptake by mycorrhizal plants.