Foliar and root uptake of N deriving from simulated atmospheric N depositions in potted apple (Malus domestica) trees

A significant human-driven increment of the available reactive nitrogen (Nr) forms has occurred during the past century at the global scale, which in turn has increased the amount of Nr deposition. Grafted apple trees (Gala / M.9 strain T337) were used in a pot experiment conducted in semicontrolled conditions, where the 15N-labelling technique allowed to trace the fate of N from ammonium nitrate (15NH4 15NO3, isotopic enrichment: 10.3 atoms %) distributed at three increasing rates (N1, N2, N4, where N2 is the double of N1 and N4 is the double of N2) either to soil or to canopy (foliar application) to simulate atmospheric N depositions. At the end of the experiment, plants were destructively sampled, and N derived from depositions (Ndfd), total N, and biomass of above and belowground organs were determined. Uptake rates ranged from 21% to 57% and the Ndfd recovery was higher for soil than for foliar application. Foliar-supplied plants showed a higher Ndfd in leaves and shoots than soil-supplied ones, while the latter showed a higher Ndfd in roots than the former. Moreover, total N in trunk, shoot axes and leaves increased with the N rates up to the level N2, with no further increase in N4. Increasing tree N availability, regardless the supply mode, increased the shoot:root N content. The fact that the N uptake rate was rather stable at increasing N rates suggests that if N from atmospheric depositions becomes increasingly available at the canopy or soil level, it will actively contribute to apple tree nutrition and account for a significant fraction of the apple tree N needs.

VNT4, a Derived Formulation of Glutacetine® Biostimulant, Improved Yield and N-Related Traits of Bread Wheat When Mixed with Urea-Ammonium-Nitrate Solution

Optimizing nitrogen use efficiency (NUE) could mitigate the adverse effects of nitrogen (N) fertilizers by limiting their environmental risks and raising agronomic performance. We studied the effects of VNT4, a derived formulation of Glutacetine® biostimulant, mixed with urea-ammonium-nitrate solution (UAN) on the growth, N-related traits and agronomic performance of winter wheat (Triticum aestivum L.). The experiment was performed under six contrasting field conditions over two years in Normandy (France), including a site where 15N labelling was undertaken. Taking into account all the sites, we report that VNT4 significantly improved grain yield (+359 kg ha−1), total grain N and NUE. VNT4 application improved growth during tillering and stem elongation (+10.7%), and N and 15N uptake between tillering and maturity (+7.3%N and +16.9%15N) leading to a higher N accumulation at maturity (+9.3%N). This N mainly originated from fertilizer (+19.4%15N) and was assimilated after the flag leaf stage in particular (+47.6%15N). These effects could be related to maintenance of physiological functions of flag leaves as suggested by the enhancement of their nutrient status (especially S, Zn and Mo). The adoption of VNT4 as a UAN additive is an efficient agronomic practice to enhance wheat productivity under an oceanic temperate climate.

Tracking the route of atmospheric nitrogen to diazotrophs colonizing buried mangrove roots

Nitrogen-fixing activity has been observed in the rhizosphere of mangrove ecosystems, suggesting a close mangrove–diazotroph relationship. In regularly flooded soil, however, the pathway by which atmospheric nitrogen reaches the diazotrophs in the rhizosphere is unknown. This study provides evidence that mangrove aerial roots serve as pathways that supply nitrogen gas to the diazotrophs colonizing buried roots. A plastic chamber was attached on the exposed part of a Rhizophora stylosa Griff prop root, and 15N2 tracer gas was injected into it. The entire root, including the below-ground part, was collected for analysis of 15N labelling and nitrogenase activity. We detected 15N labelling in buried root materials 2 h after gas injection. Compared with the δ15N contents in root material from an untreated tree, the increment was >10‰ in lateral roots. The nitrogenase activity measured on the other R. stylosa roots was highest in lateral roots, matching well with the results of 15N labelling. Our results indicate that atmospheric nitrogen is taken into aerial mangrove roots through lenticels, diffuses into the buried root system and is fixed by diazotrophs. The unusual appearance of mangrove aerial roots, which has intrigued researchers for many years, could be a key to the high productivity of mangrove ecosystems.

Anammox and partial nitritation in the mainstream of a wastewater treatment plant in a temperate region (Denmark)

The Marselisborg WWTP (Aarhus, Denmark) fed the mainstream nitrification/denitrification tanks with excess sludge from a sidestream DEMON tank for more than three years to investigate if anammox can supplement conventional nitrification/denitrification in a mainstream of a temperate region. To evaluate this long-term attempt, anammox and also denitrification rates were measured in activated sludge from the main- and sidestream at 10, 20 and 30 °C using 15N-labelling (stable isotope) experiments. The results show that anammox contributes by approximately 1% of the total nitrogen removal in the mainstream tanks and that anammox conversion rates there are approximately 800–900 times lower than in the DEMON. A distinct temperature dependence of both anammox and denitrification rates was also confirmed, however, results from different temperatures did not significantly alter relative shares, e.g. anammox rates in activated sludge from the nitrification/denitrification tanks are also negligible at 30 °C. This indicates that the anammox bacteria abundance in the nitrification/denitrification tanks is too low to play an important role and that an adaptation to lower temperatures had not occurred. Additional in situ measurements in the nitrification/denitrification tanks further revealed that full nitrification dominates over partial nitritation. Dominant nitritation-anammox is therefore excluded per se and also nitrite shunt activities are not particularly supported.

Urea and legume residues as 15N-N2O sources in a subtropical soil

In this work, we used the 15N labelling technique to identify the sources of N2O emitted by a subtropical soil following application of mineral nitrogen (N) fertiliser (urea) and residues of a legume cover crop (cowpea). For this purpose, a 45-day incubation experiment was conducted by subjecting undisturbed soil cores from a subtropical Acrisol to five different treatments: (1) control (no crop residue or fertiliser-N application); (2) 15N-labelled cowpea residue (200 μg N g–1 soil); (3) 15N-labelled urea (200 μg N g–1 soil); (4) 15N-labelled cowpea residue (100 μg N g–1 soil) + unlabelled urea (100 μg N g–1 soil); and (5) unlabelled cowpea residue (100 μg N g–1 soil) + 15N-labelled urea (100 μg N g–1 soil). Cores were analysed for total N2O formation, δ15N-N2O and δ18O-N2O by continuous flow isotope ratio mass spectrometry, as well as for total NO3–-N and NH4+-N. Legume crop residues and mineral fertiliser increased N2O emissions from soil to 10.5 and 9.7 µg N2O-N cm–2 respectively, which was roughly six times the value for control (1.5 µg N2O-N cm–2). The amount of 15N2O emitted from labelled 15N-urea (0.40–0.45% of 15N applied) was greater than from 15N-cowpea residues (0.013–0.015% of 15N applied). Unlike N-poor crop residues, urea in combination with N-rich residues (cowpea) failed to reduce N2O emissions relative to urea alone. Legume cover crops thus provide an effective mitigation strategy for N2O emissions in relation to mineral N fertilisation in climate-smart agriculture. Judging by our inconclusive results, however, using urea in combination with N-rich residues provides no clear-cut environmental advantage.

15N-Labelling and structure determination of adamantylated azolo-azines in solution

Determining the accurate chemical structures of synthesized compounds is essential for biomedical studies and computer-assisted drug design. The unequivocal determination of N-adamantylation or N-arylation site(s) in nitrogen-rich heterocycles, characterized by a low density of hydrogen atoms, using NMR methods at natural isotopic abundance is difficult. In these compounds, the heterocyclic moiety is covalently attached to the carbon atom of the substituent group that has no bound hydrogen atoms, and the connection between the two moieties of the compound cannot always be established via conventional 1H-1H and 1H-13C NMR correlation experiments (COSY and HMBC, respectively) or nuclear Overhauser effect spectroscopy (NOESY or ROESY). The selective incorporation of 15N-labelled atoms in different positions of the heterocyclic core allowed for the use of 1H-15N (J HN) and 13C-15N (J CN) coupling constants for the structure determinations of N-alkylated nitrogen-containing heterocycles in solution. This method was tested on the N-adamantylated products in a series of azolo-1,2,4-triazines and 1,2,4-triazolo[1,5-a]pyrimidine. The syntheses of adamantylated azolo-azines were based on the interactions of azolo-azines and 1-adamatanol in TFA solution. For azolo-1,2,4-triazinones, the formation of mixtures of N-adamantyl derivatives was observed. The J HN and J CN values were measured using amplitude-modulated 1D 1H spin-echo experiments with the selective inversion of the 15N nuclei and line-shape analysis in the 1D 13С spectra acquired with selective 15N decoupling, respectively. Additional spin–spin interactions were detected in the 15N-HMBC spectra. NMR data and DFT (density functional theory) calculations permitted to suggest a possible mechanism of isomerization for the adamantylated products of the azolo-1,2,4-triazines. The combined analysis of the J HN and J CN couplings in 15N-labelled compounds provides an efficient method for the structure determination of N-alkylated azolo-azines even in the case of isomer formation. The isomerization of adamantylated tetrazolo[1,5-b][1,2,4]triazin-7-ones in acidic conditions occurs through the formation of the adamantyl cation.