Inferring foliar water uptake using stable isotopes of water
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A growing number of studies have described the direct absorption of water into leaves, a phenomenon known as foliar water uptake. The resultant increase in the amount of water in the leaf can be important for plant function. Exposing leaves to isotopically enriched or depleted water sources has become a common method for establishing whether or not a plant is capable of carrying out foliar water uptake. However, a careful inspection of our understanding of the fluxes of water isotopes between leaves and the atmosphere under high humidity conditions shows that there can clearly be isotopic exchange between the two pools even in the absence of a change in the mass of water in the leaf. We provide experimental evidence that while leaf water isotope ratios may change following exposure to a fog event using water with a depleted oxygen isotope ratio, leaf mass only changes when leaves are experiencing a water deficit that creates a driving gradient for the uptake of water by the leaf. Studies that rely on stable isotopes of water as a means of studying plant water use, particularly with respect to foliar water uptake, must consider the effects of these isotopic exchange processes.
KeywordsFog Isotope dendrochronology Leaf wetting Plant–water relations Stomata
We thank L. Schmid for laboratory assistance and the reviewers for constructive comments. This research was funded through SNF (31003A_153428/1) and the European Community’s Seventh Framework Program (FP7/2007-2013) under Grant agreement Number 290605 (COFUND: PSI-FELLOW).
Author contributions statement
GRG and RS conceived of the project. GRG, MML, and LC performed the research with assistance from MA. GRG analyzed the data and wrote the paper with contributions from all the authors.
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