The Relationship between Ectomycorrhizal Fungi, Nitrogen Deposition, and Pinus massoniana Seedling Nitrogen Transporter Gene Expression and Nitrogen Uptake Kinetics

Abstract

Analyzing the molecular and physiological processes that govern the uptake and transport of nitrogen (N) in plants is central to efforts to fully understand the optimization of plant N use and the changes in the N-use efficiency in relation to changes in atmospheric N deposition changes. Here, a field experiment was conducted using the ectomycorrhizal fungi (EMF), Pisolithus tinctorius (Pt) and Suillus grevillei (Sg). The effects of N deposition were investigated using concentrations of 0 kg·N·hm−2a−1 (N0), a normal N deposition of 30 kg·N·hm−2a−1 (N30), a moderate N deposition of 60 kg·N·hm−2a−1 (N60), and a severe N deposition of 90 kg·N·hm−2a−1 (N90), with the goal of examining how these factors impacted root activity, root absorbing area, NH4+ and NO3− uptake kinetics, and the expression of ammonium and nitrate transporter genes in Pinus massoniana seedlings under different levels of N deposition. These data revealed that EMF inoculation led to increased root dry weight, activity, and absorbing area. The NH4+ and NO3− uptake kinetics in seedlings conformed to the Michaelis–Menten equation, and uptake rates declined with increasing levels of N addition, with NH4+ uptake rates remaining higher than NO3− uptake rates for all tested concentrations. EMF inoculation was associated with higher Vmax values than were observed for non-mycorrhizal plants. Nitrogen addition resulted in the upregulation of genes in the AMT1 family and the downregulation of genes in the NRT family. EMF inoculation under the N60 and N90 treatment conditions resulted in the increased expression of each of both these gene families. NH4+ and NO3− uptake kinetics were also positively correlated with associated transporter gene expression in P. massoniana roots. Together, these data offer a theoretical foundation for EMF inoculation under conditions of increased N deposition associated with climate change in an effort to improve N absorption and transport rates through the regulation of key nitrogen transporter genes, thereby enhancing N utilization efficiency and promoting plant growth. Synopsis: EMF could enhance the efficiency of N utilization and promote the growth of Pinus massoniana under conditions of increased N deposition.