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Isotopic evidence for seasonal water sources in tree xylem and forest soils
  • Marius G. Floriancic,
  • Scott Allen,
  • James Kirchner
Marius G. Floriancic
Eidgenossische Technische Hochschule Zurich Departement Bau Umwelt und Geomatik

Corresponding Author:[email protected]

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Scott Allen
University of Nevada Reno Department of Natural Resources and Environmental Science
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James Kirchner
Eidgenossische Technische Zurich Hochschule Departement Umweltsystemwissenschaften
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Abstract

Forest trees greatly influence both the routing of water downward into the subsurface and the re-routing of water upward through water uptake and transpiration. To reveal how the subsurface soil water pools used by trees change across seasons, we analyzed two years of stable isotope ratios of precipitation, soil water from different depths (using both bulk sampling and suction-cup lysimeters), and xylem in a mixed beech and spruce forest. Precipitation as well as mobile and bulk soil waters all showed a distinct seasonal signature; the seasonal amplitude decreased with depth, and mobile soil waters varied less than bulk soil waters. Xylem water signatures in both tree species were similar to the bulk soil water signatures and rather different from the mobile soil water signatures. The beech and spruce trees had different isotope ratios suggesting use of different water sources, and these differences were larger under dry antecedent conditions than wet antecedent conditions. Despite these differences, both species predominantly transpired waters with a winter-precipitation isotopic signature throughout the summer, including during wet conditions when more recent precipitation was available. Over most of the sampling dates, the fraction of recent precipitation (i.e., from the preceding 30 days) in xylem water was low, despite both species typically demonstrating use of both shallow and deeper soil waters. These results provide evidence that the soil water storages used by these trees are largely filled in winter and bypassed by recent precipitation, implying long residence times.
15 Aug 2023Submitted to Ecohydrology
15 Aug 2023Assigned to Editor
15 Aug 2023Submission Checks Completed
16 Aug 2023Review(s) Completed, Editorial Evaluation Pending
16 Aug 2023Reviewer(s) Assigned
06 Nov 2023Editorial Decision: Revise Minor