pH affects ammonium, nitrate and proton fluxes in the apical region of conifer and soybean roots

Abstract

The effect of pH on nitrate and ammonium uptake in the high-affinity transport system and low-affinity transport system ranges was compared in two conifers and one crop species. Many conifers grow on acidic soils, thus their preference for ammonium vs nitrate uptake can differ from that of crop plants, and the effect of pH on nitrogen (N) uptake may differ. Proton, ammonium and nitrate net fluxes were measured at seedling root tips and 5, 10, 20 and 30 mm from the tips using a non-invasive microelectrode ion flux measurement system in solutions of 50 or 1500 microM NH(4)NO(3) at pH 4 and 7. In Glycine max and Pinus contorta, efflux of protons was observed at pH 7 while pH 4 resulted in net proton uptake in some root regions. Pseudotsuga menziesii roots consistently showed proton efflux behind the root tip, and thus appear better adapted to maintain proton efflux in acid soils. P. menziesii's ability to maintain ammonium uptake at low pH may relate to its ability to maintain proton efflux. In all three species, net nitrate uptake was greatest at neutral pH. Net ammonium uptake in G. max and net nitrate uptake in P. menziesii were greatly reduced at pH 4, particularly at high N concentration, thus N concentration should be considered when determining optimum pH for N uptake. In P. menziesii and G. max, net N uptake was greater in 1500 than 50 microM NH(4)NO(3) solution, but flux profiles of all ions varied among species.

Positive effects of night warming on physiology of coniferous trees in late growing season: Leaf and root

“…4C), which is consistent with the uptake of NH 4 þ and NO 3 À . Similar results were also reported in Douglas-fir, lodgepole pine (Hawkins et al, 2008), soybean (Hawkins and Robbins, 2010) and Populus (Luo et al, 2013b). In addition, higher net O 2 influx (as root respiration) under artificial warming was observed (Fig.…”

“…However, there was no significant difference in the uptake rates of NH 4 þ and NO 3 À in A. faxoniana. Hawkins and Robbins (2010) reported that relative uptake rates of NH 4 þ versus NO 3 À were strongly influenced by pH. Uptake rates of NH 4 þ in Douglas-fir and lodgepole pine changed little between pH 4 and pH 7, while uptake rates of NO 3 À increased significantly between pH 4 and pH 7.…”

“…Therefore, changes in physiological activity of roots under unstable circumstances would result in corresponding shifts in plant growth and root lifespan (Yin et al, 2014). Although many conifer species are adapted to cool, acidic soils, and are expected to absorb more ammonium in comparison with nitrate (Hawkins and Robbins, 2010), nitrate reductase (NR) is generally considered to be the rate-limiting enzyme in inorganic nitrogen (N) assimilation (Young et al, 2007;Yu and Zhang, 2012) because nitrogen absorption is directly associated with the reduction rate of nitrate to nitrite (Calatayud et al, 2008;Huang et al, 2013). Root activity (as TTC, triphenyltetrazolium chloride, reducing capacity) is commonly used as an important physiological parameter for evaluation of ion and water uptake (Huang et al, 1997;Wang et al, 2006).…”

Ubiquity of Insect-Derived Nitrogen Transfer to Plants by Endophytic Insect-Pathogenic Fungi: an Additional Branch of the Soil Nitrogen Cycle

“…In soil environments where the pH is below 6, there is a significant loss of nitrogen uptake by soybean (18). The inability of M. robertsii to furnish soybean with significant levels of insect-derived nitrogen may be directly related to the pH of the soil.…”

“…M. robertsii can potentially alter the pH of the rhizosphere (19). This pH change can directly affect the activity of H ϩ -ATPase or the proton permeability of the plant cell membrane and conse- quently influence the amount of nitrogen absorbed by the plant (18).…”