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Oxygen Isotope Signals (oxygen + isotope_signal)

Distribution by Scientific Domains
Life Sciences100%

Selected Abstracts

Tracing carbon and oxygen isotope signals from newly assimilated sugars in the leaves to the tree-ring archive

PLANT CELL & ENVIRONMENT, Issue 7 2009
ARTHUR 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]

Strong seasonal disequilibrium measured between the oxygen isotope signals of leaf and soil CO2 exchange

GLOBAL CHANGE BIOLOGY, Issue 11 2010
LISA WINGATE
Abstract The oxygen isotope composition (,18O) of atmospheric CO2 is among a very limited number of tools available to constrain estimates of the biospheric gross CO2 fluxes, photosynthesis and respiration at large scales. However, the accuracy of the partitioning strongly depends on the extent of isotopic disequilibrium between the signals carried by these two gross fluxes. Chamber-based field measurements of total CO2 and CO18O fluxes from foliage and soil can help evaluate and refine our models of isotopic fractionation by plants and soils and validate the extent and pattern of isotopic disequilibrium within terrestrial ecosystems. Owing to sampling limitations in the past, such measurements have been very rare and covered only a few days. In this study, we coupled automated branch and soil chambers with tuneable diode laser absorption spectroscopy techniques to continuously capture the ,18O signals of foliage and soil CO2 exchange in a Pinus pinaster Aït forest in France. Over the growing season, we observed a seasonally persistent isotopic disequilibrium between the ,18O signatures of net CO2 fluxes from leaves and soils, except during rain events when the isotopic imbalance became temporarily weaker. Variations in the ,18O of CO2 exchanged between leaves, soil and the atmosphere were well explained by theory describing changes in the oxygen isotope composition of ecosystem water pools in response to changes in leaf transpiration and soil evaporation. [source]

Tracing carbon and oxygen isotope signals from newly assimilated sugars in the leaves to the tree-ring archive

PLANT CELL & ENVIRONMENT, Issue 7 2009
ARTHUR 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]