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.

Keywords: N management; net fluxes; non-invasive micro-test technique; productivity; proton.