Ammonia (NH3), as a dominant alkaline gas in the atmosphere, plays a vital role in Chinese urban haze formation process, but its source in urban areas of China is controversial. To identify the ...sources of urban NH3 in the semi-arid region of East Asia, real-time measurements of NH3 and NH4+ of PM2.5 in the urban atmosphere of Xi'an, inland China during the winter and summer of 2017 were performed and their stable nitrogen isotope composition were analyzed. NH3 was 38.0 ± 9.4 μg/m3 in the summer, which is 1.5 times higher than that in the winter. Concentration of NH3 in both seasons well correlated with that of PAHs in PM2.5 and the mass ratio of (BbF + BeP + IP + BghiP) to the total PAHs, suggesting that fossil fuel combustion is an important source of NH3 in Xi'an. Moreover, diurnal variation pattern of NH3 was consistent with that of CO in the summer, peaking in the morning and evening rush hours, respectively, further indicating an importance of the contribution of traffic emissions to NH3 in the city. Based on the source apportionment by using isotope mixing model, we found that 66.4% and 62.5% of NH3 in the urban atmosphere were contributed by non-agricultural sources in the summer and winter, respectively. Our work revealed that non-agricultural sources dominate the atmospheric NH3 of Xi'an, where haze pollution is still severe, and suggested that emission controls of non-agricultural NH3 could be an effective way to mitigate the air pollution problem in the semi-arid region of East Asia.
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•Non-agricultural sources were the dominant contribution for the Xi’an atmospheric NH3;•Diurnal variations of NH3 in Xi’an city were revealed during winter and summer;•Local emissions of NH3 in Xi’an were more significant on the clean days;
Rootstocks are used in modern apple production to increase productivity, abiotic and biotic stress tolerance, and fruit quality. While dwarfing for apple rootstocks has been well characterized, the ...physiological mechanisms controlling dwarfing have not. Previous research has reported rootstock effects on scion water relations. Root architecture and variability in soil moisture across rooting depths can also contribute to these differences among rootstocks in the field. To exclude these effects on rootstock behavior, scions were grafted onto four different rootstocks with varying effects on scion vigor (B.9, M.9, G.41 and G.890). Non-grafted rootstocks were also grown to examine whether the effects of rootstock occurred independently from scion grafting. Plants were grown in a greenhouse under near steady-state hydroponic conditions. Carbon (δ
C), oxygen (δ
O) and nitrogen (δ
N) isotope composition were evaluated and relationships with carbon assimilation, water relations, and shoot growth were tested. Rootstocks affected scion shoot growth, aligning with known levels of vigor for these four rootstocks, and were consistent between the two scion cultivars. Furthermore, changes in water relations influenced by rootstock genotype significantly affected leaf, stem, and root δ
C, δ
O, and δ
N. Lower δ
C and δ
O were inconsistently associated with rootstock genotypes with higher vigor in leaves, stems, and roots. G.41 had lower δ
N in roots, stems, and leaves in both grafted and ungrafted trees. The effects of rootstock on aboveground water relations were also similar for leaves of ungrafted rootstocks. This study provides further evidence that dwarfing for apple rootstocks is linked with physiological limitations to water delivery to the developing scion.
The stable nitrogen isotope composition of bivalve shell organics serves as a proxy for nitrogen fluxes in modern and past ecosystems. An essential prerequisite to reconstruct environmental variables ...from δ15N values of bivalve shells is to understand if pristine isotope signals can be retrieved from shell organics after sample pretreatment. δ15N analyses of fossil shells should be limited to the intra‐crystalline organic matrix (intra‐OM), which is trapped within biomineral units and less likely contaminated or diagenetically overprinted than inter‐crystalline organics (inter‐OM). However, it remains unclear whether the different shell organic phases (insoluble/soluble inter‐OM, intra‐OM) are isotopically distinct and whether δ15N values of intra‐OM agree with those of bulk organic matter. These questions were tackled by applying different solvents (H2O, HCl, H2O2, NaOCl) to homogenized shell powder of a modern Arctica islandica. Milli‐Q water did not alter bulk δ15N values indicating the dissolution of the inter‐OM was negligible. Acid‐extracted intra‐OM exhibited a larger isotope variation within replicates and showed a minor but significant fractionation in bulk δ15N values related to the loss of acid‐soluble components. Compared to H2O2, NaOCl oxidative treatment was more effective in cleaning inter‐OM and produced reliable bulk and amino acid (AA)‐specific δ15N data of intra‐OM. Furthermore, differences in the relative abundance and δ15N values of individual AAs suggested that the N isotope composition is not uniform within shells, and the N‐bearing content and AA composition differ between organic phases. Future studies should test the capability of bulk and CSIA‐AA δ15N proxies in fossil shells as paleoenvironmental archives.
Plain Language Summary
The nitrogen isotope ratio (15N/14N) of organics embedded in bivalve shells can be used to understand biogeochemical processes in the environment. When applying chemical solvents to clean the shells, some organic phases are inevitably lost. To evaluate the potential effects of chemical cleanings on nitrogen isotope composition (δ15N) in shell organics, we applied various solvents to modern shell samples. Most of the shell organic phases carry specific distinct amino acid (AA) compositions and therefore have different nitrogen isotope compositions. These results imply that the nitrogen‐bearing contents (such as AA) and their isotope compositions are not uniform within shells. Specifically, we compared the organics entrapped inside crystals (intra‐OM) with the total shell organics (raw‐OM). The offsets in bulk δ15N data between the two phases were mainly driven by the difference in AA proportions, while little differences were observed in δ15N values of AA. Technically, using raw shells without chemical pretreatment and using a bleaching protocol is suitable for raw‐OM and intra‐OM, respectively, to obtain the bulk and AA‐specific δ15N data. These findings indicate that raw‐OM is sufficient for bulk and AA‐specific δ15N analyses in modern bivalve shells for environmental reconstructions and provide a framework to study the fossil shells.
Key Points
Organic phases in modern bivalve shells carry different nitrogen isotope compositions
The amino acid composition differed between total organics and intra‐organics, resulting in different nitrogen isotope data
The optimum growth and development of wheat depend on nitrogen (N) from different sources and its assimilation mechanisms. Experiments were conducted on 47 wheat genotypes to understand N ...assimilation and fractionation dynamics in different tissues of wheat. The genotypes were grown in two growing systems (VPC- a mixture of vermiculite and perlite and Hydroponic) under N-limiting (LN) and N-optimum (ON) conditions for various growth periods: GS13, GS15, GS19, GS39, and GS65. Nitrogen isotope composition (δ
15
N,
n
= 624) and nitrogen concentration (%N,
n
= 624) were measured in the root, stem, leaf, and ear of each genotype. In the VPC system, 33 genotypes were analyzed where the roots are
15
N enriched with low %N and the shoots are
15
N depleted with high %N at GS15 suggesting higher fractionation in roots, active primary distribution of N, and effective N cycling. In the Hydroponic system, 14 genotypes were analyzed where %N in the shoot is higher than the root in ON conditions, whereas δ
15
N values are higher in the root than the shoot in LN conditions. Nevertheless, the δ
15
N and %N levels are inversely proportional irrespective of the genotypes in both growing systems. The genotypes grown in the VPC system have distinctly higher δ
15
N values (higher isotopic fractionation causing
15
N abundance) in both root and shoot than those in the Hydroponic system under all conditions of external nitrogen availability, suggesting higher N uptake and active primary distribution in the VPC system.
The flag leaf has been traditionally considered as the main contributor to grain nitrogen. However, during the reproductive stage, other organs besides the flag leaf may supply nitrogen to developing ...grains. Therefore, the contribution of the ear and other organs to the nitrogen supplied to the growing grains remains unclear. It is important to develop phenotypic tools to assess the relative contribution of different plant parts to the N accumulated in the grains of wheat which may helps to develop genotypes that use N more efficiently. We studied the effect of growing conditions (different levels of water and nitrogen in the field) on the nitrogen contribution of the spike and different vegetative organs of the plant to the grains. The natural abundance of δ
N and total N content in the flag blade, peduncle, whole spike, glumes and awns were compared to the δ
N and total N in mature grains to trace the origin of nitrogen redistribution to the grains. The δ
N and total N content of the different plant parts correlated positively with the δ
N and total N content of mature grains suggesting that all organs may contribute a portion of their N content to the grains. The potential contribution of the flag blade to grain N increased (by 46%) as the growing conditions improved, whereas the potential contribution of the glumes plus awns and the peduncle increased (46 and 31%, respectively) as water and nitrogen stress increased. In general, potential contribution of the ear providing N to growing grains was similar (42%) than that of the vegetative parts of the plants (30-40%), regardless of the growing conditions. Thus, the potential ear N content could be a positive trait for plant phenotyping, especially under water and nitrogen limiting conditions. In that sense, genotypic variability existed at least between old (tall) and modern (semidwarf) cultivars, with the ear from modern genotypes exhibiting less relative contribution to the total grain N. The combined use of δ
N and N content may be used as an affordable tool to assess the relative contribution of different plant parts to the grain N in wheat.
Biochar has strong potential to improve nitrogen (N) use efficiency in both agricultural and horticultural systems. Biochar is usually co-applied with full rates of fertiliser. However, the extent to ...which N cycling can be affected after biochar application to meet plant N requirement remains uncertain. This study aimed to explore N cycling up to 2 years after biochar application. We applied pine woodchip biochar at 0, 10 and 30 t ha
−1
(B0, B10, B30, respectively) in a macadamia orchard and evaluated the N isotope composition (δ
15
N) of soil, microbial biomass and macadamia leaves. Soil total N (TN) and inorganic N pools were also measured up to 2 years after biochar application. Biochar did not alter soil TN but soil NO
3
−
-N increased at months 12 and 24 after biochar application. Soil NO
3
−
-N concentrations were always over ideal levels of 15 μg g
−1
in B30 throughout the study. Stepwise regression indicated that foliar δ
15
N decreases after biochar application were explained by increased NO
3
−
-N concentrations in B30. Foliar TN and photosynthesis were not affected by biochar application. The soil in the high rate biochar plots had excess NO
3
−
-N concentrations (over 30 μg g
−1
) from month 20 onwards. Therefore, N fertiliser applications could be adjusted to prevent excessive N inputs and increase farm profitability.
Atmospheric nitrogen deposition affects nitrogen isotope composition (δ15N) in plants. However, both negative effect and positive effect have been reported. The effects of climate on plant δ15N have ...not been corrected for in previous studies, this has impeded discovery of a true effect of atmospheric N deposition on plant δ15N. To obtain a more reliable result, it is necessary to correct for the effects of climatic factors. Here, we measured δ15N and N contents of plants and soils in Baiwangshan and Mount Dongling, north China. Atmospheric N deposition in Baiwangshan was much higher than Mount Dongling. Generally, however, foliar N contents showed no difference between the two regions and foliar δ15N was significantly lower in Baiwangshan than Mount Dongling. The corrected foliar δ15N after accounting for a predicted value assumed to vary with temperature was obviously more negative in Baiwangshan than Mount Dongling. Thus, this suggested the necessity of temperature correction in revealing the effect of N deposition on foliar δ15N. Temperature, soil N sources and mycorrhizal fungi could not explain the difference in foliar δ15N between the two regions, this indicated that atmospheric N deposition had a negative effect on plant δ15N. Additionally, this study also showed that the corrected foliar δ15N of bulk data set increased with altitude above 1300m in Mount Dongling, this provided an another evidence for the conclusion that atmospheric N deposition could cause 15N–depletion in plants.
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•Temperature effect was corrected in studying effect of N deposition on plant δ15N.•Accounting for temperature effect accurately revealed N deposition effect on δ15N.•Foliar δ15N was smaller in a higher N deposition area than a lower deposition area.•Atmospheric N deposition exerted a negative effect on plant δ15N.
Simultaneous analysis of carbon and nitrogen isotope ratios by SIMS was applied for the first‐time to a natural diamond from the Kelsey Lake kimberlite, State Line Distinct, Colorado (UWD‐1). This in ...situ procedure is faster, reduces sample size for analysis, and measures both isotope ratios from a single ~ 10 μm diameter pit, a critical advantage for zoned diamonds. The carbon isotope ratio (expressed as δ13CVPDB) of the bulk UWD‐1 crystal, determined by the conventional combustion method in the present study, is ‐5.9‰ ± 0.2‰ (VPDB, 2s). Nitrogen mass fraction (N) and isotope ratio (expressed as δ15NAir) were determined by stepwise combustion and gas‐source mass‐spectrometry, resulting in 553 ± 64 μg g‐1 and ‐6.7‰ ± 1.1‰ (Air, 2s), respectively. Secondary ions of 12C2‐, 12C13C‐, 12C14N‐, and 12C15N‐ were simultaneously measured by SIMS using three Faraday cups and one electron multiplier. The spot‐to‐spot reproducibility of δ13C and δ15N values for the UWD‐1 (178 spots on sixteen chips, 10 μm spots), were 0.3‰ and 1.6‰, respectively (2s). While 12C14N‐/12C2‐ ratios, which are an indicator for N, varied up to 12% among these sixteen chips, such variation did not correlate with either δ13C or δ15N values. We propose that UWD‐1 is a suitable reference sample for microscale in situ analysis of δ13C and δ15N values in diamond samples.
Key Points
Single spot (~ 10 μm) simultaneous δ13C and δ15N determination was performed using SIMS on UWD‐1, resulting in ± 0.3‰ and ± 1.6‰ precision (2s), respectively.
The δ13C and δ15N measurements on natural diamond.
The new analytical reference sample for diamonds that are frequently small and zoned in microscale.
Foliar nitrogen isotope (δsup.15N) composition patterns have been linked to soil N, mycorrhizal fractionation, and within-plant fractionations. However, few studies have examined the potential ...importance of the direct foliar uptake of gaseous reactive N on foliar δsup.15N. Using an experimental set-up in which the rate of mycorrhizal infection was reduced using a fungicide, we examined the influence of mycorrhizae on foliar δsup.15N in potted red maple (Acer rubrum) seedlings along a regional N deposition gradient in New York State. Mycorrhizal associations altered foliar δsup.15N values in red maple seedlings from 0.06 to 0.74 % across sites. At the same sites, we explored the predictive roles of direct foliar N uptake, soil δsup.15N, and mycorrhizae on foliar δsup.15N in adult stands of A. rubrum, American beech (Fagus grandifolia), black birch (Betula lenta), and red oak (Quercus rubra). Multiple regression analysis indicated that ambient atmospheric nitrogen dioxide (NO.sub.2) concentration explained 0, 69, 23, and 45 % of the variation in foliar δsup.15N in American beech, red maple, red oak, and black birch, respectively, after accounting for the influence of soil δsup.15N. There was no correlation between foliar δsup.13C and foliar %N with increasing atmospheric NO.sub.2 concentration in most species. Our findings suggest that total canopy uptake, and likely direct foliar N uptake, of pollution-derived atmospheric N deposition may significantly impact foliar δsup.15N in several dominant species occurring in temperate forest ecosystems. Keywords Nitrogen isotope composition * Foliar uptake * Nitrogen cycling * Reactive nitrogen * Temperate forest
Drought stress is a major limiting factor of soybean Glycine max (L.) Merr. production around the world. Soybean plants can ameliorate this stress with improved water-saving, sustained N
fixation ...during water deficits, and/or limited leaf hydraulic conductance. In this study, carbon isotope composition (δ
C), which can relate to variation in water-saving capability, was measured. Additionally, nitrogen isotope composition (δ
N) and nitrogen concentration that relate to nitrogen fixation were evaluated. Decrease in transpiration rate (DTR) of de-rooted soybean shoots in a silver nitrate (AgNO
) solution compared to deionized water under high vapor pressure deficit (VPD) conditions was used as a surrogate measurement for limited leaf hydraulic conductance. A panel of over 200 genetically diverse soybean accessions genotyped with the SoySNP50K iSelect BeadChips was evaluated for the carbon and nitrogen related traits in two field environments (Athens, GA in 2015 and 2016) and for transpiration response to AgNO
in a growth chamber. A multiple loci linear mixed model was implemented in FarmCPU to perform genome-wide association analyses for these traits.
Thirty two, 23, 26, and nine loci for δ
C, δ
N, nitrogen concentration, and transpiration response to AgNO
, respectively, were significantly associated with these traits. Candidate genes that relate to drought stress tolerance enhancement or response were identified near certain loci that could be targets for improving and understanding these traits. Soybean accessions with favorable breeding values were also identified. Low correlations were observed between many of the traits and the genetic loci associated with each trait were largely unique, indicating that these drought tolerance related traits are governed by different genetic loci.
The genomic regions and germplasm identified in this study can be used by breeders to understand the genetic architecture for these traits and to improve soybean drought tolerance. Phenotyping resources needed, trait heritability, and relationship to the target environment should be considered before deciding which of these traits to ultimately employ in a specific breeding program. Potential marker-assisted selection efforts could focus on loci which explain the greatest amount of phenotypic variation for each trait, but may be challenging due to the quantitative nature of these traits.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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![Foliar δ[sup.15]N is affect...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0029-8549/small "Foliar δ[sup.15]N is affected by foliar nitrogen uptake, soil nitrogen, and mycorrhizae along a nitrogen deposition gradient")
