The Effect of 18O‐labelled Water Vapour on the Oxygen Isotope Ratio of Water and Assimilates in Plants at High Humidity

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  • Our understanding of how temporal variations of atmospheric water vapour and its isotopic composition (δ18OV) influence water and assimilates in plants remains limited, restricting our ability to used18O as a tracer of ecophysiological processes.
  • We exposed oak (Quercus robur) saplings under wet and dry soil moisture conditions to 18O-depleted water vapour (c.-200&) at high relative humidity (c. 93%) for 5 h, simulating a fog event. We then traced the step change in δ18OV into water and assimilates (e.g. sucrose, hexoses, quercitol and starch) in the leaf lamina, main veins and twigs over 24 h.
  • The immediated δ18OV effect was highest for δ18O of leaf lamina water, but 40% lower on δ18O of main vein water. To a smaller extent, we also observed changes in δ18O of twig xylem water. Depending on the individual assimilation rate of each plant, the 18O-label was partitioned among different assimilates, with highest changes in δ18O of starch/sucrose and lowest in δ18O of quercitol. Additionally, 18O-label partitioning and allocation towards leaf starch and twig phloem sugars was influenced by the plant water status.
  • Our results have important implications for water isotope heterogeneity in plants and for our understanding of how the δ18O signal is incorporated into biomarkers.


This article was originally published in New Phytologist, volume 217, issue 1, in 2017.


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