Simon D. Kelly

Fertilizer nitrogen isotope signatures

There has been considerable recent interest in the potential application of nitrogen isotope analysis in discriminating between organically and conventionally grown crops. A prerequisite of this approach is that there is a difference in the nitrogen isotope compositions of the fertilizers used in organic and conventional agriculture. We report new measurements of δ15N values for synthetic nitrogen fertilizers and present a compilation of the new data with existing literature nitrogen isotope data. Nitrogen isotope values for fertilizers that may be permitted in organic cultivation systems are also reported (manures, composts, bloodmeal, bonemeal, hoof and horn, fishmeal and seaweed based fertilizers). The δ15N values of the synthetic fertilizers in the compiled dataset fall within a narrow range close to 0‰ with 80% of samples lying between−2 and 2‰ and 98.5% of the data having δ15N values of less than 4‰ (mean=0.2‰ n=153). The fertilizers that may be permitted in organic systems have a higher mean δ15N value of 8.5‰ and exhibit a broader range in δ15N values from 0.6 to 36.7‰ (n=83). The possible application of the nitrogen isotope approach in discriminating between organically and conventionally grown crops is discussed in light of the fertilizer data presented here and with regard to other factors that are also important in determining crop nitrogen isotope values.

TILLING Mutants of Lotus japonicus Reveal That Nitrogen Assimilation and Fixation Can Occur in the Absence of Nodule-Enhanced Sucrose Synthase

In all plant species studied to date, sucrose synthase occurs as multiple isoforms. The specific functions of the different isoforms are for the most part not clear. Six isoforms of sucrose synthase have been identified in the model legume Lotus japonicus, the same number as in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa). The genes encoding these isoforms are differentially expressed in all plant organs examined, although one, LjSUS4, is only expressed in flowers. LjSUS1 is the most highly expressed in all plant organs tested, except root nodules, where LjSUS3 accounts for more than 60% of the total SUS transcripts. One gene, LjSUS2, produces two transcripts due to alternative splicing, a feature not observed in other species to date. We have isolated plants carrying ethyl methanesulfonate-induced mutations in several SUS genes by targeting-induced local lesions in genomes reverse genetics and examined the effect of null alleles of two genes, LjSUS1 and LjSUS3, on nodule function. No differences were observed between the mutants and wild-type plants under glasshouse conditions, but there was evidence for a nitrogen-starvation phenotype in the sus3-1 mutant and severe impairment of growth in the sus1-1/sus3-1 double mutant under specific environmental conditions. Nodules of sus3-1 mutant plants retained a capacity for nitrogen fixation under all conditions. Thus, nitrogen fixation can occur in L. japonicus nodules even in the absence of LjSUS3 (the major nodule-induced isoform of SUS), so LjSUS1 must also contribute to the maintenance of nitrogen assimilation.

Assessing the authenticity of single seed vegetable oils using fatty acid stable carbon isotope ratios (13C12C)

Abstract The authenticity of single seed vegetable oils which utilise the C3 photosynthetic pathway was investigated using gas chromatography-combustion-stable isotope ratio mass spectrometry (GC-C-SIRMS). Samples of authentic groundnut, palm, rapeseed and sunflower oils were derivatised to form fatty acid methyl esters (FAMEs) and their carbon isotope ratios ( 13 C 12 C ) determined. In-house reference materials (IHRMs) and internal standards were used routinely to monitor the extraction procedure and SIRMS measurement. These materials demonstrated the consistent performance of the technique. δ13C%. data for the authentic vegetable oil fatty acids fell into the narrow range of −27.6%. to −32.1%. However, the values within the oil varieties considered were significantly different. The data from sunflower oils were such that they could be separated from the other varieties by canonical discriminant analysis. The determination of fatty acid carbon isotope ratios may therefore provide an additional indication of the varietal authenticity of oils which use the C3 photosynthetic pathway.

Geographical origin differentiation of saffron spice (Crocus sativus L. stigmas) - Preliminary investigation using chemical and multi-element (H, C, N) stable isotope analysis.

A preliminary study of the bulk hydrogen, carbon and nitrogen stable isotope composition of 28 authentic saffron samples produced from Crocus sativus L. cultivated in the typical production areas of Western Macedonia in Greece (8), Khorasan Province in Iran (7), Sardinia in Italy (6) and Castilla-La Mancha in Spain (7) is described. A chemical characterisation of 16 key quality parameters was also completed on the same samples by UV-Vis, HPLC and GC analyses. Multivariate analysis of the data revealed that 60.7% of saffron samples could be correctly assigned to their respective production countries using the chemical parameters. However, the combined bio-element stable isotope data reliably classified 100% of the saffron samples according to their respective geographical origins using posterior cross validation. Further work is required to establish the long-term stability of these models with respect to different years of production and other major producers such as India and Morocco.

Investigation into the use of carbon isotope ratios (13C/12C) of Scotch whisky congeners to establish brand authenticity using gas chromatography-combustion-isotope ratio mass spectrometry

Abstract Volatile congeners of whisky have been analysed by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Acetaldehyde, ethyl acetate, n-propanol, isobutanol and amyl alcohol from a popular blended whisky have been separated using established GC conditions and their δ13C%. values determined. Eight samples of the whisky blend taken over the last 2 years of production have been analysed to allow the authentic range to be determined. A radar diagram has been used to graphically represent the δ13C%. data. This was used as a simple means of comparing the carbon isotope profiles of whiskies. Two other whisky samples were analysed and shown to differ from the whisky blend on the basis of the δ13C values.

Application of Nitrogen and Carbon Stable Isotopes (δ15N and δ13C) to Quantify Food Chain Length and Trophic Structure

Increasingly, stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) are used to quantify trophic structure, though relatively few studies have tested accuracy of isotopic structural measures. For laboratory-raised and wild-collected plant-invertebrate food chains spanning four trophic levels we estimated nitrogen range (NR) using δ15N, and carbon range (CR) using δ13C, which are used to quantify food chain length and breadth of trophic resources respectively. Across a range of known food chain lengths we examined how NR and CR changed within and between food chains. Our isotopic estimates of structure are robust because they were calculated using resampling procedures that propagate variance in sample means through to quantified uncertainty in final estimates. To identify origins of uncertainty in estimates of NR and CR, we additionally examined variation in discrimination (which is change in δ15N or δ13C from source to consumer) between trophic levels and among food chains. δ15N discrimination showed significant enrichment, while variation in enrichment was species and system specific, ranged broadly (1.4‰ to 3.3‰), and importantly, propagated variation to subsequent estimates of NR. However, NR proved robust to such variation and distinguished food chain length well, though some overlap between longer food chains infers a need for awareness of such limitations. δ13C discrimination was inconsistent; generally no change or small significant enrichment was observed. Consequently, estimates of CR changed little with increasing food chain length, showing the potential utility of δ13C as a tracer of energy pathways. This study serves as a robust test of isotopic quantification of food chain structure, and given global estimates of aquatic food chains approximate four trophic levels while many food chains include invertebrates, our use of four trophic level plant-invertebrate food chains makes our findings relevant for a majority of ecological systems.

Is it really organic? - Multi-isotopic analysis as a tool to discriminate between organic and conventional plants

Novel procedures for analytical authentication of organic plant products are urgently needed. Here we present the first study encompassing stable isotopes of hydrogen, carbon, nitrogen, oxygen, magnesium and sulphur as well as compound-specific nitrogen and oxygen isotope analysis of nitrate for discrimination of organically and conventionally grown plants. The study was based on wheat, barley, faba bean and potato produced in rigorously controlled long-term field trials comprising 144 experimental plots. Nitrogen isotope analysis revealed the use of animal manure, but was unable to discriminate between plants that were fertilised with synthetic nitrogen fertilisers or green manures from atmospheric nitrogen fixing legumes. This limitation was bypassed using oxygen isotope analysis of nitrate in potato tubers, while hydrogen isotope analysis allowed complete discrimination of organic and conventional wheat and barley grains. It is concluded, that multi-isotopic analysis has the potential to disclose fraudulent substitutions of organic with conventionally cultivated plants.

Sr isotope measurements in beef: analytical challenge and first results

AbstractThe strontium isotope ratio (87Sr/86Sr) in beef, derived from 206 European cattle, has been measured. These cattle were located in 12 different European regions within France, Germany, Greece, Ireland, Italy, Spain and the UK. As animal protein is known to be a difficult material on which to conduct Sr isotope analysis, several investigations were undertaken to develop and improve the sample preparation procedure. For example, Sr isotope analysis was performed directly on freeze-dried meat and defatted dry mass from the same samples. It was found that enormous differences—sometimes exceeding the measurement uncertainty—could occur between the fractions and also within one sample even if treated in the same manner. These variations cannot be definitely allocated to one cause but are most likely due to inhomogeneities caused by physiological and biochemical processes in the animals as post mortem contamination during analytical processing could be excluded. For further Sr isotope measurements in meat, careful data handling is recommended, and for the authentic beef samples within this project, it was decided to use only freeze-dried material. It can be demonstrated, however, that Sr isotope measurements in beef proteins are a valuable tool for authentication of geographic origin. Although partly overlapping, some of the European sampling sites could be discriminated even by only using 87Sr/86Sr. FigureBox plot diagram displaying 87Sr/86Sr in authentic beef samples ordered by Trace sampling sites

The use of pyrolytic techniques to estimate site specific isotope data of vanillin

Abstract Two pyrolysis techniques have been investigated for providing site specific isotopic information for vanillin. A Curie Point pyrolyser was used to fragment vanillin samples of known carbon isotopic composition. Hydroxy benzaldehyde, phenol and catechol were produced and identified by gas chromatography mass spectrometry (Py-GC/MS). Their carbon isotopic ratios were measured by gas chromatography combustion isotope ratio mass spectrometry (Py-GC/C-IRMS). The extreme conditions required to produce this fragmentation led to isotopic mixing so that, under the conditions employed, the fragmentation products did not retain isotopic information which could be used for authentication purposes. A second pyrolytic technique generating carbon monoxide under continuous flow conditions for isotope ratio mass spectrometry (Py-CF-IRMS) was used to study vanillin samples. The carbon monoxide gave information on the oxygen isotopes present in the vanillin. In addition, it appears that the carbon–oxygen bond of the parent vanillin molecule is retained so that the carbon isotopic content of oxygen bearing carbons can be measured. Comparison of carbon isotope data measured using this procedure agreed well with the known values of standard materials. The oxygen isotopes also provided useful information on the source discrimination of vanillin samples from fossil fuel and plant sources. Py-CF-IRMS may therefore provide a rapid and convenient technique for authenticating vanillin and other important food flavours.

Individual foraging specialisation in a social mammal: the European badger ( Meles meles )

Individual specialisation has been identified in an increasing number of animal species and populations. However, in some groups, such as terrestrial mammals, it is difficult to disentangle individual niche variation from spatial variation in resource availability. In the present study, we investigate individual variation in the foraging niche of the European badger (Meles meles), a social carnivore that lives in a shared group territory, but forages predominantly alone. Using stable isotope analysis, we distinguish the extent to which foraging variation in badgers is determined by social and spatial constraints and by individual differences within groups. We found a tendency for individual badgers within groups to differ markedly and consistently in their isotope values, suggesting that individuals living with access to the same resources occupied distinctive foraging niches. Although sex had a significant effect on isotope values, substantial variation within groups occurred independently of age and sex. Individual differences were consistent over a period of several months and in some instances were highly consistent across the two years of the study, suggesting long-term individual foraging specialisations. Individual specialisation in foraging may, therefore, persist in populations of territorial species not solely as a result of spatial variation in resources, but also arising from individuals selecting differently from the same available resources. Although the exact cause of this behaviour is unknown, we suggest that specialisation may occur due to learning trade-offs which may limit individual niche widths. However, ecological factors at the group level, such as competition, may also influence the degree of specialisation.