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Isotope Enrichment (isotope + enrichment)
Kinds of Isotope Enrichment Selected AbstractsComparison of 85Kr and 3H Apparent Ground-Water Ages for Source Water Vulnerability in the Collyer River Catchment, Maine,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2008William C. Sidle Abstract:, Apparent ground-water ages as determined by the noble gas isotope 85Kr and the water isotope 3H are compared. Refined gas extraction methodology at the wellhead permits efficient collection of Kr for 85Kr isotope enrichment. 85Kr isochrones elucidate areas of much younger ground-water ages than 3H. Declining 3H activities in the catchment prevent its correlation with the youngest measured 85Kr ages. Source water for most drinking water supplies in the Collyer River catchment is recharged within 40 years BP (2004). Mean-age (,) transport modeling suggests uncertainty of ground-water ages is greatest in the central basin area. [source] Is heterosis in maize mediated through better water use?NEW PHYTOLOGIST, Issue 2 2010José Luis Araus Summary ,Heterosis increases yield potential and improves adaptation to stress in maize (Zea mays); however, the underlying mechanisms remain elusive. ,A set of tropical inbred lines and their hybrids were grown in the field for 2 yr under three different water regimes. First-year plant water use was evaluated by measuring instantaneous traits (stomatal conductance (gs) and steady-state chlorophyll fluorescence (Fs)) in individual leaves together with time-integrative traits, which included mineral accumulation in the whole leaves of plants and oxygen isotope enrichment above source water (,18O) and carbon isotope discrimination (,13C) in the same pooled leaves and in mature kernels. Second-year water use was evaluated by measuring leaf temperature, gs and relative water content (RWC). ,Within each growing condition, hybrids showed higher Fs, mineral accumulation, RWC, and lower leaf temperature, ,18O and ,13C than inbred lines. Therefore, hybrids had a better water status than inbred lines, regardless of the water conditions. Differences in grain yield across growing conditions were explained by differences in water-use traits, with hybrids and inbred lines following a common pattern. Within each growing condition, most variations in grain yield, between hybrids and inbred lines, were also explained by differences in plant water-use traits. ,Heterosis in tropical maize seems to be mediated by improved water use, irrespective of the water conditions during growth. [source] Oxygen isotope enrichment (,18O) reflects yield potential and drought resistance in maizePLANT CELL & ENVIRONMENT, Issue 11 2009LLORENÇ CABRERA-BOSQUET ABSTRACT Measurement of stable isotopes in plant dry matter is a useful phenotypic tool for speeding up breeding advance in C3 crops exposed to different water regimes. However, the situation in C4 crops is far from resolved, since their photosynthetic metabolism precludes (at least in maize) the use of carbon isotope discrimination. This paper investigates the use of oxygen isotope enrichment (,18O) as a new secondary trait for yield potential and drought resistance in maize (Zea mays L). A set of tropical maize hybrids developed by the International Maize and Wheat Improvement Center was grown under three contrasting water regimes in field conditions. Water regimes clearly affected plant growth and yield. In accordance with the current theory, a decrease in water input was translated into large decreases in stomatal conductance and increases in leaf temperature together with concomitant 18O enrichment of plant matter (leaves and kernels). In addition, kernel ,18O correlated negatively with grain yield under well-watered and intermediate water stress conditions, while it correlated positively under severe water stress conditions. Therefore, genotypes showing lower kernel ,18O under well-watered and intermediate water stress had higher yields in these environments, while the opposite trend was found under severe water stress conditions. This illustrates the usefulness of ,18O for selecting the genotypes best suited to differing water conditions. [source] Tracing carbon and oxygen isotope signals from newly assimilated sugars in the leaves to the tree-ring archivePLANT CELL & ENVIRONMENT, Issue 7 2009ARTHUR GESSLER ABSTRACT The analysis of ,13C and ,18O in tree-ring archives offers retrospective insights into environmental conditions and ecophysiological processes. While photosynthetic carbon isotope discrimination and evaporative oxygen isotope enrichment are well understood, we lack information on how the isotope signal is altered by downstream metabolic processes. In Pinus sylvestris, we traced the isotopic signals from their origin in the leaf water (,18O) or the newly assimilated carbon (,13C), via phloem sugars to the tree-ring, over a time-scale that ranges from hours to a growing season. Seasonally, variable 13C enrichment of sugars related to phloem loading and transport did lead to uncoupling between ,13C in the tree-ring, and the ci/ca ratio at the leaf level. In contrast, the oxygen isotope signal was transferred from the leaf water to the tree-ring with an expected enrichment of 27,, with time-lags of approximately 2 weeks and with a 40% exchange between organic oxygen and xylem water oxygen during cellulose synthesis. This integrated overview of the fate of carbon and oxygen isotope signals within the model tree species P. sylvestris provides a novel physiological basis for the interpretation of ,13C and ,18O in tree-ring ecology. [source] Assessing environmental and physiological controls over water relations in a Scots pine (Pinus sylvestris L.) stand through analyses of stable isotope composition of water and organic matterPLANT CELL & ENVIRONMENT, Issue 1 2007ELKE BRANDES ABSTRACT This study investigated the influence of meteorological, pedospheric and physiological factors on the water relations of Scots pine, as characterized by the origin of water taken up, by xylem transport as well as by carbon isotope discrimination (,13C) and oxygen isotope enrichment (,18O) of newly assimilated organic matter. For more than 1 year, we quantified ,2H and ,18O of potential water sources and xylem water as well as ,13C and ,18O in twig and trunk phloem organic matter biweekly, and related these values to continuously measured or modelled meteorological parameters, soil water content, stand transpiration (ST) and canopy stomatal conductance (Gs). During the growing season, ,18O and ,2H of xylem water were generally in a range comparable to soil water from a depth of 2,20 cm. Long residence time of water in the tracheids uncoupled the isotopic signals of xylem and soil water in winter. ,18O but not ,13C in phloem organic matter was directly indicative of recent environmental conditions during the whole year. ,18O could be described applying a model that included 18O fractionation associated with water exchange between leaf and atmosphere, and with the production of organic matter as well as the influence of transpiration. Phloem ,13C was assumed to be concertedly influenced by Gs and photosynthetically active radiation (PAR) (as a proxy for photosynthetic capacity). We conclude that isotope signatures can be used as effective tools (1) to characterize the seasonal dynamics in source and xylem water, and (2) to assess environmental effects on transpiration and Gs of Scots pine, thus helping to understand and predict potential impacts of climate change on trees and forest ecosystems. [source] A new approach to aid the characterisation and identification of metabolites of a model drug; partial isotope enrichment combined with novel formula elucidation softwareRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2009Kirsten Hobby This work describes the identification of ,isotopically enriched' metabolites of 4-cyanoaniline using the unique features of the software package ,Spectral Simplicity'. The software is capable of creating the theoretical mass spectra for partially isotope-enriched compounds, and subsequently performing an elemental composition analysis to give the elemental formula for the ,isotopically enriched' metabolite. A novel mass spectral correlation method, called ,FuzzyFit', was employed. ,FuzzyFit' utilises the expected experimental distribution of errors in both mass accuracy and isotope pattern and enables discrimination between statistically probable and improbable candidate formulae. The software correctly determined the molecular formulae of ten previously described metabolites of 4-cyanoaniline confirming the technique of partial isotope enrichment can produce results analogous to standard methodologies. Six previously unknown species were also identified, based on the presence of the unique ,designer' isotope ratio. Three of the unknowns were tentatively identified as N-acetylglutamine, O-methyl-N acetylglucuronide and a putative fatty acid conjugate. The discovery of a significant number of unknown species of a model drug with a comprehensive history of investigation highlights the potential for enhancement to the analytical process by the use of ,designer' isotope ratio compounds. The ,FuzzyFit' methodology significantly aided the elucidation of candidate formulae, by provision of a vastly simplified candidate formula data set. Copyright © 2008 John Wiley & Sons, Ltd. [source] Identification of the D3h Isomer of Carbon Trioxide (CO3) and Its Implications for Atmospheric ChemistryCHEMPHYSCHEM, Issue 12 2006Corey S. Jamieson Abstract The CO3 molecule is considered an important reaction intermediate in the atmospheres of Earth and Mars for quenching electronically excited oxygen atoms and in contributing to the anomalous 18O isotope enrichment. The geometry of the CO3 intermediate plays an important role in explaining these effects; however, only the cyclic (C2v) isomer has been experimentally confirmed so far. Here, we report on the first spectroscopic detection of the acyclic (D3h) isomer of carbon trioxide (12C16O3) via its ,1 and ,2 vibrational modes centered around 1165 cm,1 under matrix isolation conditions; the identification of the 12C18O3, 13C16O3, 13C18O3, 16O12C18O2, and 18O12C16O2 isotopomers of the acyclic isomer confirms the assignments. [source] Carbon and nitrogen dynamics in zero-water exchange shrimp culture as indicated by stable isotope tracersAQUACULTURE RESEARCH, Issue 11 2002M A Epp Abstract The uptake and assimilation of nitrogen and carbon by shrimp were measured in 1200 L mesocosms using stable isotope enrichments. Labels were added via 15N-, 13C-glycine and amino acid mixtures in feeds or as 15NH4+ to pond water. Label was incorporated into shrimp via algal growth indicating that up to 31% of nitrogen requirements were derived from pond ecosystem dynamics. This value is low in comparison with other shrimp aquaculture isotopic tracer studies but is probably due to differences in shrimp-rearing conditions. Direct incorporation of the enriched feed label was low in shrimp muscle tissue (3.3% for 13C-glycine, 5.9% for 15N-glycine and 7.8% for 15N-amino acid mixture). Mass balance calculations indicate the remaining shrimp biomass was derived from feed, but loss of label into solution during feeding led to underestimation based on tracers. Incorporation of isotopic labels into feed as large molecular weight proteinaceous or microencapsulated/fat-coated compounds is recommended to prevent dissolution and loss. [source] | |||||||||||||