Characteristics of NH4+ and NO3− Fluxes in Taxodium Roots under Different Nitrogen Treatments

Abstract

To understand the characteristics of net NH4+ and NO3− fluxes and their relation with net H+ fluxes in Taxodium, net fluxes of NH4+, NO3− and H+ were detected by a scanning ion-selective electrode technique under different forms of fixed nitrogen (N) and experimental conditions. The results showed that higher net NH4+ and NO3− fluxes occurred at 2.1–3.0 mm from the root apex in T. ascendens and T. distichum. Compared to NH4+ or NO3− alone, more stable net NH4+ and NO3 − fluxes were found under NH4NO3 supply conditions, of which net NH4+ flux was promoted at least 1.71 times by NO3−, whereas net NO3− flux was reduced more than 81.66% by NH4+ in all plants, which indicated that NH4+ is preferred by Taxodium plants. T. ascendens and T. mucronatum had the largest net NH4+ and total N influxes when NH4+:NO3− was 3:1.15N Atom% and activities of N assimilation enzymes were improved by single N fertilization in the roots of T. distichum. In most cases, net H+ fluxes were tightly correlated with net NH4+ and NO3- fluxes. Thus, both N forms and proportions could affect N uptake of Taxodium. These findings could provide useful guidance for N management for better productivity of Taxodium plants.