Nitrate Transporter Gene Expression and Kinetics of Nitrate Uptake by Populus × canadensis 'Neva' in Relation to Arbuscular Mycorrhizal Fungi and Nitrogen Availability

Fei Wu; Fengru Fang; Na Wu; Li Li; Ming Tang

doi:10.3389/fmicb.2020.00176

Nitrate Transporter Gene Expression and Kinetics of Nitrate Uptake by Populus × canadensis 'Neva' in Relation to Arbuscular Mycorrhizal Fungi and Nitrogen Availability

Front Microbiol. 2020 Feb 28:11:176. doi: 10.3389/fmicb.2020.00176. eCollection 2020.

Authors

Fei Wu^{1

2

3}, Fengru Fang², Na Wu⁴, Li Li², Ming Tang¹

Affiliations

¹ State Key Laboratory of Conservation and Utilization of Subtropical Agro-bioresources, Guangdong Laboratory of Lingnan Modern Agriculture, Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China.
² College of Forestry, Northwest A&F University, Yangling, China.
³ Key Laboratory of State Forestry and Grassland Administration on Forest Ecosystem Protection and Restoration of Poyang Lake Watershed, College of Forestry, Jiangxi Agricultural University, Nanchang, China.
⁴ School of Life Science, Shanxi Datong University, Datong, China.

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 (V _max) 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.

Keywords: arbuscular mycorrhiza; nitrate transporter gene; nitrate uptake kinetics; nitrogen fertilization; poplar.