Absorption and partitioning mechanism of nitrogen oxides by typical greening species of tree in Beijing

In this study, we analyzed the uptake of nitrogen dioxide (NO₂) and its processes of distribution in various organs of different typical greening species of trees and the differences in its uptake by these different species using the ¹⁵N stable isotope tracer method under the gradient of three NO₂ concentration treatments, namely, low, medium and high. These experiments were conducted using one-time artificial fumigation to provide necessary data and theoretical support for the selection and application of species of greening trees in urban gardens. The treatments of fumigation with different concentrations of NO₂ showed that the leaves of the six species of trees had the highest content of ¹⁵N. The organs that were the most effective at taking up ¹⁵N were the leaves in broadleaf trees and the branches in conifers. The content of ¹⁵N per unit of the leaves (0.0058–2.0486 μg/g) increased in parallel with the concentration of fumigant and then was rapidly transported to various organs in the tree. This caused different degrees of changes in other organs. The total content of ¹⁵N per unit was higher in the broadleaf species (0.0129–2.3171 μg/g) than in the conifers (0.0296–0.1260 μg/g). The leaves of broadleaf trees were the most effective at taking up ¹⁵N (0.0054–1.3228 %) under medium and high concentrations of fumigant with the exception of ginkgo. The ability of each organ of the other broadleaf species was leaves>branches>trunks>roots, and the branches of conifers were the most effective parts of the trees at taking up NO₂ under three concentrations of fumigants (0.0789–0.4005 %). The highest rate of distribution of ¹⁵N was found in the leaves (48.14–99.53 %) in all six species under different concentrations of fumigant, and the distribution in the other organs varied to different degrees.