15N Natural Abundance Research Articles

13C and 15N natural isotope abundance in urothelium and bladder cancer ti – preliminary study

13C and 15N natural isotope abundance in urothelium and bladder cancer ti – preliminary study

Temporal Variation in Community Composition of Root Associated Endophytic Fungi and Carbon and Nitrogen Stable Isotope Abundance in Two Bletilla Species (Orchidaceae).

Mycorrhizae are an important energy source for orchids that may replace or supplement photosynthesis. Most mature orchids rely on mycorrhizae throughout their life cycles. However, little is known about temporal variation in root endophytic fungal diversity and their trophic functions throughout whole growth periods of the orchids. In this study, the community composition of root endophytic fungi and trophic relationships between root endophytic fungi and orchids were investigated in Bletilla striata and B. ochracea at different phenological stages using stable isotope natural abundance analysis combined with molecular identification analysis. We identified 467 OTUs assigned to root-associated fungal endophytes, which belonged to 25 orders in 10 phyla. Most of these OTUs were assigned to saprotroph (143 OTUs), pathotroph-saprotroph (63 OTUs) and pathotroph-saprotroph-symbiotroph (18 OTUs) using FunGuild database. Among these OTUs, about 54 OTUs could be considered as putative species of orchid mycorrhizal fungi (OMF). For both Bletilla species, significant temporal variation was observed in the diversity of root endophytic fungi. The florescence and emergence periods had higher fungal community richness of total species and endemic species than did other periods. Both Bletilla species were dominated by Agaricomycetes and Basidiomycota fungi throughout the whole year; however, their abundances varied between two Bletilla species and among phenological stages. Meanwhile, the ranges of 13C and 15N natural abundance were also highly dynamic across all growth stages of Bletilla species. Compared with the surrounding autotrophic plants, significant 13C enrichments (ε13C) were found across all phenological stages, while significant 15N enrichment in the florescence period and strong 15N depletion during the fruiting period were found for both Bletilla species. We can deduce that both Bletilla species obtained carbon from root endophytic fungi during the whole year. Additionally, the temporal varying tendency of root endophytic fungal diversity was consistent with 13C enrichments, which was also accord with the nutritional requirement of plant.

Changes of δ15N values during the volatilization process after applying urea on soil.

Ammonia (NH3) volatilized from soils plays an important role in N cycle and air pollution, thus it is important to trace the emission source and predict source contributions to development strategies mitigating the environmental harmful of soil NH3 volatilization. The measurements of 15N natural abundance (δ15N) could be used as a complementary tool for apportioning emissions sources to resolve the contribution of multiple NH3 emission sources to air NH3 pollution. However, information of the changes of δ15N-NH3 values during the whole volatilization process under different N application rates are currently lacking. Hence, to fill this gap, we conducted a 15-day incubation experiment included different urea-N application rates to determine δ15N values of NH3 during volatilization process. Results showed that volatilization process depleted 15N in NH3. The average δ15N value of NH3 volatilized from the 0, 20, 180, and 360kgN ha-1 treatment was-16.2±7.3‰,-26.0±5.4‰,-34.8±4.8‰, and-40.6±5.7‰. Overall, δ15N-NH3 values ranged from-46.0‰ to-4.7‰ during the whole volatilization process, with lower in higher urea-N application treatments than those in control. δ15N-NH3 values during the NH3 volatilization process were much lower than those of the primary sources, soil (-3.4±0.1‰) and urea (-3.6±0.1‰). Therefore, large isotopic fractionation may occur during soil volatilization process. Moreover, negative relationships between soil NH4+-N and NH3 volatilization rate and δ15N-NH3 values were observed in this study. Our results could be used as evidences of NH3 source apportionments and N cycle.

On inorganic N uptake by vascular plants: Can 15N tracer techniques resolve the NH4+ versus NO3− “preference” conundrum?

AbstractThe relative uptake by plants of the two ionic nitrogen (N) forms, ammonium (NH4+) and nitrate (NO3−), has been the subject of much interest during the past 50 years, resulting in a considerable scientific literature. The general idea is that plants have choice, resulting in preference for either one mineral N form or the other. Unfortunately, there is no specific definition of preference or agreement on how it should be measured. In this review, we critically examine the alternative techniques that have been used to measure the relative uptake of NH4+ and NO3− by plants, including those based on unlabelled sources, 15N‐enriched mineral N forms and variations in the 15N natural abundance of mineral N sources. The main difficulty with using unlabelled N is the antecedent N in plant tissue prior to the imposition of treatments. Although 15N‐enrichment overcomes this obstacle, it is nevertheless difficult to separate uptake as 15NH4+, uptake as 15NO3− and uptake as 15NO3− derived from the nitrification of 15NH4+. With 15N natural abundance, isotopic fractionation during plant uptake complicates the interpretation of data. There is increasing evidence that plants exhibit flexibility or plasticity with respect to the use of mineral N forms rather than preference.Highlights The concept of plant preference for NH4+ or NO3− forms of mineral N is examined Experiments using 15N‐enrichment and 15N natural abundance are reviewed The direct uptake of 15NO3− is confounded with the uptake of 15NO3− derived from nitrified 15NH4+ Plants exhibit plasticity rather than preference in the acquisition of ammonium and nitrate

Nitrogen acquisition and 15N-fertiliser recovery efficiency of sugarcane cultivar RB92579 inoculated with five diazotrophs

We aimed to evaluate N acquisition and 15N-fertiliser recovery efficiency of sugarcane as a function of N fertilisation and inoculation with plant growth-promoting diazotrophic bacteria (PGPDB) during the first crop season. A field experiment was performed with a randomized complete block design consisting of four replications and four treatments: control without N and without inoculation; control without N but with inoculation of a mixture of five strains of diazotrophic bacteria; N treatment (50 kg ha−1 N-urea) without inoculation; and N treatment with inoculation. Over seven harvests, we evaluated crop growth, biomass accumulation, N content, and N recovery using 15N-urea (excess of 1.5% atoms 15N). In addition, the contribution of biological N fixation (BNF) was measured using the 15N natural abundance technique in the plots without N fertiliser application. Inoculation with the mixture of five PGPDB strains increased the yield by 15% and N content in the shoots by 18% over the cycle. The average contribution of N fertiliser in plant N nutrition was 13%; other sources accounted for a large part of N in the shoots. Plants received N via BNF in 31% (average) of the treatments during the plant cycle; however, inoculation did not interfere with this process. The recovery efficiency of 15N-fertiliser was 50% in this first cycle with no differences among inoculation treatments. Nitrogen fertiliser applied to sugarcane resulted in a low impact on N accumulation, and a single application of an inoculant improved plant growth by mechanisms other than BNF.

The linkage of 13C and 15N soil depth gradients with C:N and O:C stoichiometry reveals tree species effects on organic matter turnover in soil

The knowledge of tree species dependent turnover of soil organic matter (SOM) is limited, yet required to understand the carbon sequestration function of forest soil. We combined investigations of 13C and 15N and its relationship to elemental stoichiometry along soil depth gradients in 35-year old monocultural stands of Douglas fir (Pseudotsuga menziesii), black pine (Pinus nigra), European beech (Fagus sylvatica) and red oak (Quercus rubra) growing on a uniform post-mining soil. We investigated the natural abundance of 13C and 15N and the carbon:nitrogen (C:N) and oxygen:carbon (O:C) stoichiometry of litterfall and fine roots as well as SOM in the forest floor and mineral soil. Tree species had a significant effect on SOM δ13C and δ15N reflecting significantly different signatures of litterfall and root inputs. Throughout the soil profile, δ13C and δ15N were significantly related to the C:N and O:C ratio which indicates that isotope enrichment with soil depth is linked to the turnover of organic matter (OM). Significantly higher turnover of OM in soils under deciduous tree species depended to 46% on the quality of litterfall and root inputs (N content, C:N, O:C ratio), and the initial isotopic signatures of litterfall. Hence, SOM composition and turnover also depends on additional—presumably microbial driven—factors. The enrichment of 15N with soil depth was generally linked to 13C. In soils under pine, however, with limited N and C availability, the enrichment of 15N was decoupled from 13C. This suggests that transformation pathways depend on litter quality of tree species.

Effect of a 10-day fish or copra oil oral nutritional supplementation on plasma bulk 15N and 13C natural isotopic abundances in women with metastatic breast cancer

Rationale: Natural isotopic abundances (NIAs) of food and organ/whole body metabolic activity determine 13C and 15N NIAs in many biological media in health and disease. We took advantage of a randomized, double-blind, controlled Phase III clinical trial testing the effect of isocaloric isonitrogenous oral nutritional supplements (ONS) containing fish (FO) or copra oil (CO) on progression-free survival in women with metastatic breast cancer.

Plasma amino acid pools in the umbilical cord artery show lower 15N natural isotope abundance relative to the maternal venous pools

ABSTRACT 15N natural isotope abundance (NIA) is systematically higher in infants’ hair than in that of their mothers at birth. This study aimed to investigate this difference in plasma pools. We compared 15N NIA values for plasma amino acid (AA) pools (free + protein-bound) in the umbilical cord artery (UCA) and vein (UCV) and in the maternal vein (MV) at birth. This preliminary study included 7 mother–infant dyads. Whole plasma was treated (HCl) to hydrolyze protein. Following derivatization, AAs were separated using gas chromatography and compound-specific 15N NIA values were measured on-line using an isotope ratio monitoring mass spectrometer. 15N NIA plasma AA pools in the UCA and UCV were highly correlated to the MV, r 2 > 0.89 and r 2 > 0.88 (both P < 10−4) respectively. The full model found a significant effect of sampling compartment (P = 0.02) and AA type (P < 0.0001) on 15N NIA plasma AA values. 15N NIA plasma AA was 0.74 ‰ higher (P = 0.01) in the MV than in the UCA. This study indicates that a decrease in 15N NIA for plasma AA pools occurs in the fetal–placental unit. Trial registration: ClinicalTrials.gov identifier: NCT00607061.

Temporal and Vertical Oxygen Gradients Modulate Nitrous Oxide Production in a Seasonally Anoxic Fjord: Saanich Inlet, British Columbia

AbstractNitrous oxide (N2O) is a strong greenhouse gas and an ozone depleting agent. In marine environments, N2O is produced biologically via ammonium oxidation, nitrite, and nitrate reduction. The relative importance of these principle production pathways is strongly influenced by oxygen availability. We conducted 15N tracer experiments of N2O production in parallel with measurements of N2O concentration and natural abundance isotopes/isotopomers in Saanich Inlet, a seasonally anoxic fjord, to investigate how temporal and vertical oxygen gradients regulate N2O production pathways and rates. In April, June, and August 2018, the depth of the oxic‐anoxic interface (dissolved oxygen = 2.5 μmol L−1 isoline) progressively deepened from 110 to 160 m. Within the oxygenated and suboxic water column, N2O supersaturation coincided with peak ammonium oxidation activity. Conditions in the anoxic deep water were potentially favorable to N2O production from nitrate and nitrite reduction, but N2O undersaturation was observed indicating that N2O consumption exceeded rates of production. In October, tidal mixing introduced oxygenated water from outside the inlet, displacing the suboxic and anoxic deep water. This oxygenation event stimulated N2O production from ammonium oxidation and increased water column N2O supersaturation while inhibiting nitrate and nitrite reduction to N2O. Results from 15N tracer incubation experiments and natural abundance isotopomer measurements both implicated ammonium oxidation as the dominant N2O production pathway in Saanich Inlet, fueled by high ammonium fluxes (0.6–3.5 nmol m−2 s−1) from the anoxic depths. Partial denitrification contributed little to water column N2O production because of low availability of nitrate and nitrite.

Rotation Benefits From N2-Fixing Grain Legumes to Cereals: From Increases in Seed Yield and Quality to Greater Household Cash-Income by a Following Maize Crop

We investigated Bambara groundnut, groundnut, mung bean, cowpea and black gram for use as biofertilizers in cropping systems. The 15N natural abundance technique was used to measure N2 fixation in this study. The percent N derived from fixation by mung bean (Vigna radiata L. Wilczek), Bambara groundnut (Vigna subterranea L. Verdc.), cowpea (Vigna unguiculata L.Walp.), black gram (Vigna mungo L.) and groundnut (Arachis hypogaea L was 98, 83, 79, 66 and 45% respectively. Nitrogen contribution by these legumes was 83, 67, 39, 36 and 32 kg.ha-1 respectively for Bambara groundnut, groundnut, mung bean, black gram and cowpea. Maize grain yield without N fertilizer was 2449, 2291, 2204, 2046 and 1671 kg.ha-1 respectively for maize following groundnut, Bambara groundnut, cowpea, mung bean, black gram and maize. Grain yield increase of maize after legumes without N fertilizer was 47, 46, 37, 32 and 22% respectively for groundnut, Bambara groundnut, cowpea, mung bean, and black gram. Supplying N0 up to N60 to maize plants increased shoot DM from 3264 to 4279 kg.ha-1, yield grain from 2184 to 3586 kg.ha-1, and whole-plant DM from 5448 to 7865 kg.ha-1, which represented 31, 64 and 44% increase with N fertilizer supply from 0 to 60 kg N ha-1. Symbiotic N benefit of preceding legumes to maize without N fertilizer was 20 to 40 kg N. ha-1 in fertilizer equivalents. The preceding legumes increased maize grain concentrations of P, Ca, S, Fe, Mn and Zn in zero-N plots relative to maize after maize. There was 225, 222, 180, 154 and 108% increase in marginal returns of maize after groundnut, Bambara groundnut, cowpea, mung bean and black gram respectively without N fertilizer.

Variations in the natural 13C and 15N abundance of plants and soils under long-term N addition and precipitation reduction: interpretation of C and N dynamics

BackgroundThe nitrogen isotope natural abundance (δ15N) provides integrated information on ecosystem N dynamics, and carbon isotope natural abundance (δ13C) has been used to infer how water-using processes of plants change in terrestrial ecosystems. However, how δ13C and δ15N abundances in plant life and soils respond to N addition and water availability change is still unclear. Thus, δ13C and δ15N abundances in plant life and soils were used to investigate the effects of long-time (10 years) N addition (+ 50 kg N·ha− 1·yr− 1) and precipitation reduction (− 30% of throughfall) in forest C and N cycling traits in a temperate forest in northern China.ResultsWe analyzed the δ13C and δ15N values of dominant plant foliage, litterfall, fungal sporophores, roots, and soils in the study. The results showed that δ15N values of foliage, litterfall, and surface soil layer’s (0–10 cm) total N were significantly increased by N addition, while δ15N values of fine roots and coarse roots were considerably decreased. Nitrogen addition also significantly increased the δ13C value of fine roots and total N concentration of the surface soil layer compared with the control. The C concentration, δ13C, and δ15N values of foliage and δ15N values of fine roots were significantly increased by precipitation reduction, while N concentration of foliage and litterfall significantly decreased. The combined effects of N addition and precipitation reduction significantly increased the δ13C and δ15N values of foliage as well as the δ15N values of fine roots and δ13C values of litterfall. Furthermore, foliar δ15N values were significantly correlated with foliage δ13C values, surface soil δ15N values, surface soil C concentration, and N concentrations. Nitrogen concentrations and δ13C values of foliage were significantly correlated with δ15N values and N concentrations of fine roots.ConclusionsThis indicates that plants increasingly take up the heavier 15N under N addition and the heavier 13C and 15N under precipitation reduction, suggesting that N addition and precipitation reduction may lead to more open forest ecosystem C and N cycling and affect plant nutrient acquisition strategies.

Differences in contribution of biological nitrogen fixation to yield performance of common bean cultivars as assessed by the 15N natural abundance technique

Identification of variability in biological N2 fixation (BNF) contribution among common bean (Phaseolus vulgaris L.) cultivars under field conditions requires a reliable methodology. This study aimed to assess different common bean cultivars for plant growth and grain yield and to quantify the BNF contribution to the crop using the 15N natural abundance technique. Two field experiments were conducted in an Oxisol in Brazil over two consecutive years, with eight common bean cultivars inoculated with rhizobium or fertilized with mineral N. Plants were analysed at mid-pod filling stage (two weeks after full-flowering) and at grain maturity. BNF was estimated by the 15N natural abundance technique. Average grain yields were 1614 or 2942 kg ha−1 in Experiment I, and 3284 or 3919 kg ha−1 in Experiment II, with rhizobium inoculation or mineral N, respectively. The average contributions of N derived from atmosphere were 14 and 26%, and amounts of N2-fixed were 7 and 22 kg N ha−1, in bean plants at mid-pod filling, respectively, in Experiment I and Experiment II. The contributions of BNF increase when common bean crop reached its optimum yield potential even though soil N was the most important source for the plants. There is good relationship between δ15N values of grains and shoots, provided cultivars are of similar growth habit. The 15N natural abundance technique allowed identifying cultivars with relatively high BNF capability for commercial crop and breeding purposes.

Cover Crop Selection by Jointly Optimizing Biomass Productivity, Biological Nitrogen Fixation, and Transpiration Efficiency: Application to Two Crotalaria Species

Crotalaria spectabilis and Crotalaria juncea are cover crops (CC) that are used in many different regions. Among the main attributes of these species are their high potential for biomass production and biological fixation of nitrogen (BNF). Attempting to maximize these attributes, while minimizing water consumption through high transpiration efficiency (TE), is a challenge in the design of sustainable agricultural rotations. In this study, the relationship between biomass productivity, BNF, and TE in C. spectabilis and C. juncea was evaluated. For this purpose, an experiment was carried out under controlled conditions without water limitations and using non-inoculated soil. BNF was determined by the natural abundance of 15N, while TE was estimated by several different methods, such as gravimetric or isotopic method (13C). C. juncea produced 42% less dry matter, fixed 28% less nitrogen from the air, and had 20% less TE than C. spectabilis. TE results in both species were consistent across methodologies. Under simulated environmental conditions of high temperature and non-limiting soil water content, C. spectabilis was a relatively more promising species than C. juncea to be used as CC.

Assessment of Nitrogen Fixation by Mungbean Genotypes in Different Soil Textures Using 15N Natural Abundance Method

Ensuring food and nutritional security in light of high climate variability and a rapidly growing population remains a challenge. Mungbean (Vigna radiata (L.) Wilczek) is a short duration, drought-tolerant, and ureide-exporting legume crop capable of symbiotic atmospheric nitrogen fixation. Estimates of biological N2 fixation by mungbean in different soil textures have not been extensively studied. We conducted this study to evaluate plant growth and N2 fixation of five mungbean genotypes (Berken, 8735, IC 8972-1, STB#122, 223) inoculated with Bradyrhizobium spp. and grown on loamy sand and silt loam soils under glasshouse conditions. Mungbean dry matter yield, δ15N values, shoot content, amounts of N-fixed, and soil N uptake were all higher on the silt loam soil compared to the loamy sand soil, demonstrating the effects of soil properties on plant growth and N2 fixation potential. Among genotypes, IC 8972-1 produced the highest biomass (7.85 g plant−1), shoot N content (200 mg plant−1), and soil N uptake (155 mg plant−1) than other genotypes. The significant interaction between soil texture and genotypes for root dry matter and %Ndfa indicates the major role of legume root-nodule bacteria in symbiotic N2 fixation. This study demonstrated that N2 fixation in mungbean is affected by both genotypes and soil properties, illustrating the need to consider soil properties in order to maximize N contribution from mungbean to agricultural production systems.

Overseeding legumes in natural grasslands: Impacts on root biomass and soil organic matter of commercial farms

Overseeding legumes in natural grasslands coupled with phosphorous fertilization are management practices oriented to increase forage production and quality, and to restore nutrient losses generated by livestock. Several studies show increases in forage due to this practice, but less is known about impacts on soil fertility and carbon sequestration. The objective of this study was to evaluate under real farm conditions changes in root C and N stocks and soil organic carbon (SOC) and nitrogen (SON) stocks in two different soil pools, the particulate organic matter (POM) and the mineral associated organic matter (MAOM), after the introduction in natural grasslands of a legume species, Lotus subbiflorus cv. “El Rincón”, accompanied with phosphorous fertilization. We also evaluated changes in the natural abundance of 15N and 13C in soils and roots to understand changes in N fixation and species composition. We selected 12 adjacent paddocks of natural grasslands (NG) and natural grasslands overseeded with legumes and fertilized with phosphorous (NGLP) located in commercial farms in Uruguay. We found that overseeding legumes increased root C and N stocks and SOC and SON stocks in some farms but decreased them in others. On average, no significant differences arose between NGLP and NG paddocks in total stocks of 0–30 cm depth. However, higher C stocks were observed in POM of NGLP paddocks in 0–5 cm layer and lower contents in 5–10 cm layer indicating a change in the vertical distribution of C in POM. Changes in δ15N suggest that atmospheric N is being fixed by legumes in NGLP paddocks, but not translated into more N or C stocks in the MAOM fraction, probably due to high N losses promoted by cattle grazing. Our work suggests that carbon sequestration can be achieved after legumes introduction in grazed natural grasslands but will depend on grazing management practices.

The origin of N isotopic discrimination and its relationship with feed efficiency in fattening yearling bulls is diet-dependent.

Nitrogen (N) isotopic discrimination (i.e. the difference in natural 15N abundance between the animal proteins and the diet; Δ15N) is known to correlate with N use efficiency (NUE) and feed conversion efficiency (FCE) in ruminants. However, results from the literature are not always consistent across studies, likely due to isotopic discrimination pathways that may differ with the nature of diets. The objective of the present study was to assess at which level, from rumen to tissues, Δ15N originates and becomes related to NUE and FCE in fattening yearling bulls when they are fed two contrasted diets. Twenty-four Charolais yearling bulls were randomly divided into two groups and fed during 8 months, from weaning to slaughter, either 1) a high starch diet based on corn silage supplying a balanced N to energy ratio at the rumen level (starch) or 2) a high fiber diet based on grass silage supplying an excess of rumen degradable N (fiber). All animals were slaughtered and samples of different digestive pools (ruminal, duodenal, ileal and fecal contents), animal tissues (duodenum, liver and muscle), blood and urine were collected for each animal. Ruminal content was further used to isolate liquid-associated bacteria (LAB), protozoa and free ammonia, while plasma proteins were obtained from blood. All samples along with feed were analyzed for their N isotopic composition. For both diets, the digestive contribution (i.e. the N isotopic discrimination occurring before absorption) to the Δ15N observed in animal tissues accounted for 65 ± 11%, leaving only one third to the contribution of post-absorptive metabolism. Concerning the Δ15N in digestive pools, the majority of these changes occurred in the rumen (av. Δ15N = 2.12 ± 0.66‰), with only minor 15N enrichments thereafter (av. Δ15N = 2.24 ± 0.41‰), highlighting the key role of the rumen on N isotopic discrimination. A strong, significant overall relationship (n = 24) between Δ15N and FCE or NUE was found when using any post-absorptive metabolic pool (duodenum, liver, or muscle tissues, or plasma proteins; 0.52 < r < 0.73; P ≤ 0.01), probably as these pools reflect both digestive and post-absorptive metabolic phenomena. Fiber diet compared to starch diet had a lower feed efficiency and promoted higher (P ≤ 0.05) Δ15N values across all post-absorptive metabolic pools and some digestive pools (ruminal, duodenal, and ileal contents). The within-diet relationship (n = 12) between Δ15N and feed efficiency was not as strong and consistent as the overall relationship, with contrasted responses between the two diets for specific pools (diet x pool interaction; P ≤ 0.01). Our results highlight the contrasted use of N at the rumen level between the two experimental diets and suggests the need for different equations to predict FCE or NUE from Δ15N according to the type of diet. In conclusion, rumen digestion and associated microbial activity can play an important role on N isotopic discrimination so rumen effect related to diet may interfere with the relationship between Δ15N and feed efficiency in fattening yearling bulls.

Identification of N‐ or O‐Alkylation of Aromatic Nitrogen Heterocycles and N‐Oxides Using 1H–15N HMBC NMR Spectroscopy

A series of representative diazines and pyridine N‐oxides were subjected to alkylation using several different alkylating agents. The 15N NMR chemical shifts (δN values) of the diazines, pyridine N‐oxides and derived alkylation products were determined using 1H‐15N HMBC NMR spectroscopy at natural 15N abundance. The changes in the 15N NMR chemical shifts (Δ(δN) values) that occurred on going from starting materials to products in these reactions were analyzed. N‐alkylation of diazines resulted in large upfield shifts of the δN values of the alkylated nitrogen (of the order of 100 ppm or greater). While O‐alkylation of pyridine N‐oxides resulted in upfield shifts of the δN values of the N‐(alkoxy)pyridinium nitrogen, the Δ(δN) values were of a much smaller magnitude (ca. –42 ppm) than those observed for N‐alkylations of diazines. Nitrogen NMR spectroscopic data from the literature of relevance to alkylation of azines, diazines, azine N‐oxides and diazine N‐oxides was gathered together, and using this in tandem with our 15N NMR spectroscopic data, we have been able to corroborate our observations on the trends observed in the Δ(δN) values associated with N‐ and O‐alkylation reactions of aromatic N‐heterocycles and N‐oxides. An analysis protocol that relies on synergistic evaluation of 1H‐15N HMBC and 1H‐13C HMBC NMR spectra has been developed that enables unambiguous diagnosis of the occurrence of N‐alkylation of aromatic N‐heterocycles and O‐alkylation of aromatic N‐oxides.

Contrasting soil C and N dynamics inferred from δ13C and δ15N values along a climatic gradient in southern China

Secondary grasslands reestablished after deforestation in subtropical and tropical regions greatly alter terrestrial carbon (C) and nitrogen (N) dynamics and their associated ecosystem functions. However, reliable evaluations of C and N dynamics in secondary grasslands across regional climatic gradient remain challenging. We investigated natural 13C and 15N abundance in plants and soil as well as their associations with environmental factors (including climatic, plant and edaphic variables) from 20 sites across a 600 km climatic gradient in secondary grasslands of southern China. The δ13C values in plants and soil declined with increasing mean annual precipitation (MAP) but increased as the mean annual temperature (MAT) increased. These changes were mostly attributed to the shift in plant functional group between C4 and C3. In contrast, increasing MAP and decreasing MAT had positive effects on soil δ15N values, which were mainly related to changes in edaphic factors, including soil pH, soil C and N content and soil C:N ratios. Our findings indicate inverse patterns and different controls on soil δ13C and δ15N values along the climatic gradient, providing novel insights into the underlying mechanisms of ecosystem C and N dynamics in response to climate and vegetation change in secondary grasslands.

Natural 15N abundance in specific amino acids indicates associations between transamination rates and residual feed intake in beef cattle.

Improving the ability of animals to convert feed resources into food for humans is needed for more sustainable livestock systems. Genetic selection for animals eating less while maintaining their performance (i.e., low residual feed intake [RFI]) appears a smart strategy but its effectiveness relies on high-throughput animal phenotyping. Here, we explored plasma nitrogen (N) isotope ratios in an attempt to identify easily superior young bulls in terms of RFI. For this, 48 Charolais young bulls fed two contrasting diets (corn vs. grass silage diets) were selected from a larger population as extreme RFI animals (24 low-RFI vs. 24 high-RFI) and their plasma analyzed for natural 15N abundance (δ15N) in the whole protein (bulk protein) and in the individual protein-bound amino acids (PbAA). For the first time, we showed that the δ 15N in plasma bulk protein differed (P = 0.007) between efficient (low-RFI) and inefficient (high-RFI) cattle regardless of diet. Furthermore, most analyzed PbAA followed the same trend as the bulk protein, with lower (P < 0.05) δ 15N values in more efficient (low-RFI) compared with less efficient (high-RFI) cattle, again regardless of diet. The only three exceptions were Phe, Met, and Lys (P > 0.05) for which the first metabolic reaction before being catabolized does not involve transamination, a pathway known naturally to enrich AAs in 15N. The contrasted isotopic signatures across RFI groups only in those PbAA undergoing transamination are interpreted as differences in transamination rates and N-use efficiency between low- and high-RFI phenotypes. Natural isotopic N signatures in bulk proteins and specific PbAA can be proposed as biomarkers of RFI in growing beef cattle fed different diets. However, the current study cannot delineate whether this effect only occurs post-absorption or to some extent also in the rumen. Our data support the conclusion that most efficient cattle in terms of RFI upregulate N conservation mechanisms compared with less efficient cattle and justify future research on this topic.

Insights into nitrogen fixing traits and population structure analyses in cowpea (Vigna unguiculata L. Walp) accessions grown in Ghana.

With legumes, symbiotic N2 fixation can meet the species N demand and reduce the over-reliance on chemical fertilizers in tropical regions where N deficiency is a major factor limiting crop yields and increased agricultural sustainability. Therefore, to optimize the use of cowpea (Vigna unguiculata L. Walp) germplasm in effective breeding, evaluation of genetic diversity and quantification of N2 fixation are essential prerequisites. The aim of this study was to explore the level of diversity using SSR markers and N2-fixing traits in a set of cowpea germplasm grown in Ghana. We analysed 49 cowpea accessions collected from Northern Ghana using qualitative vegetative and N2 fixation traits, and simple sequence repeat (SSR) markers. Experimental field results revealed considerable morpho-physiological variation for plant growth habits, grain yield and symbiotic performance between and among the cowpea accessions. Results from both the 15N natural abundance and ureides in the xylem sap were able to descriminate between high and low levels of N2 fixation in cowpea accessions. Five subpopulations were identified within accessions inferred from STRUCTURE2.3.4. A general linear model was used to assess the association of SSR markers with N2-fixing traits. There were significant (p ≤ 0.05) links betweenSSR markers andsymbiosis-related traits such as nodule number, nodule dry weight, shoot dry weight, N-fixed, N derived from air (Ndfa), and relative uried-N (RU-N).