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hydrogen isotope ratios
lipid biosynthesis
aquatic plants
c-4
grasses
seasonal-variation
modern angiosperms
individual lipids
epicuticular wax
d/h ratios
fractionation
Abstract:
Leaf wax n-alkanes from barley (Hordeum vulgure) from a field in Switzerland exhibited changes in delta D values on the order of 20 parts per thousand over a growing season, while source water (soil water) and leaf water varied by 40 parts per thousand. Additionally the seasonal variability in delta D values of leaf wax n-alkanes of different barley leaves can only be found across different leaf generations (i.e. leaves that were produced at different times during the growing season) while n-alkane delta D values did not vary significantly within a leaf generation. Interestingly, delta D values of n-alkanes correlated best with the delta D values of leaf water at midday of the sampling day but showed no significant correlation with soil water (e.g. precipitation) delta D values. These results provide empirical evidence that leaf wax delta D values record leaf water enrichment, and therefore integrate the isotopic effects of precipitation and evapotranspiration. Our results show that leaf wax n-alkane delta D values from grasses are 'locked in' early during leaf development and hence record the environmental drivers of leaf water enrichment, such as vapor pressure deficit (VPD). Our data have important implications for the interpretation of paleorecords of leaf wax delta D. We suggest that leaf wax n-alkane delta D values from sedimentary records could be used to estimate changes in the degree of leaf water enrichment and hence VPD. (C) 2010 Elsevier Ltd. All rights reserved.