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Opportunistic Short-term Compensatory Water Uptake by Subalpine Trees Observed via in situ Water Isotope Measurements
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  • Matthias Sprenger,
  • Stefan Seeger,
  • Max Berkelhammer,
  • Nathaniel Bogie,
  • Raymond J. Hess,
  • Wendy S Brown,
  • Sylvain Kuppel,
  • James O'Neil Knighton
Matthias Sprenger
Lawrence Berkeley National Laboratory

Corresponding Author:[email protected]

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Stefan Seeger
University of Freiburg, Germany
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Max Berkelhammer
University of Illinois at Chicago
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Nathaniel Bogie
San Jose State University
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Raymond J. Hess
Rutgers University
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Wendy S Brown
Rocky Mountain Biological Laboratory
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Sylvain Kuppel
Institut de Recherche pour le Développement
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James O'Neil Knighton
University of Connecticut
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Abstract

Tree water source variation in semi-arid ecosystems is important to understand because climatic shifts towards lower snowpack and increased drought affect water availability in subalpine forests of the western US.
Here, we use daily in situ measurements of stable isotopes (2H) in soil and tree water, soil matric potential and sap flow to study tree water uptake dynamics. We instrumented three soil profiles down to 90 cm, as well as three Aspen and Engelmann Spruce trees near Gothic, Colorado, in the East River watershed. We observed the fate of natural 2H variations in rainfall, soil, and plants from June to October 2022, and in August 2023 we conducted a 2H labeled water irrigation experiment.
Our observations showed that transpiration was reduced by all trees, but partially compensated by shifting the dominant water source from 60 to 90 cm within days of a dry period. Intense rainfall quickly shifted the plant water uptake partially to top soil layers. Changes in water uptake depths were similar between aspen and spruce, but rainfall infiltration was low in the spruce stand due to high canopy interception. Therefore spruce transpiration was lower and relied more on snowmelt. However, both species relied on snowmelt to sustain transpiration and groundwater recharge from monsoonal rains was not observed. These findings highlight the important role of snowmelt stored in the deep soil layers for subalpine forest drought response and the dominant fate of monsoonal rainfall to become transpiration rather than recharging groundwater and streams in the Upper Colorado River.
21 Oct 2024Submitted to ESS Open Archive
21 Oct 2024Published in ESS Open Archive