Rapid increases in shrubland and forest intrinsic water-use efficiency during an ongoing megadrought

Globally, intrinsic water-use efficiency (iWUE) has risen dramatically over the past century in concert with increases in atmospheric CO₂ concentration. This increase could be further accelerated by long-term drought events, such as the ongoing multidecadal “megadrought” in the American Southwest. H...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2021-12, Vol.118 (52), p.1-6
Main Authors: Kannenberg, Steven A., Driscoll, Avery W., Szejner, Paul, Anderegg, William R. L., Ehleringer, James R.
Format: Article
Language:English
Subjects:
Aridity
Biological Sciences
Carbon dioxide
Carbon Dioxide - metabolism
Carbon dioxide concentration
Carbon Isotopes
Climate Change
Drought
Droughts
Drying
Ecosystem
ENVIRONMENTAL SCIENCES
Forests
iWUE
Pine trees
Plant species
Planting density
Plants
Sensitivity
Shrublands
Shrubs
stable isotopes
tree rings
Trees - metabolism
Trends
Vegetation
Water - metabolism
Water Cycle
Water use
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Summary:Globally, intrinsic water-use efficiency (iWUE) has risen dramatically over the past century in concert with increases in atmospheric CO₂ concentration. This increase could be further accelerated by long-term drought events, such as the ongoing multidecadal “megadrought” in the American Southwest. However, direct measurements of iWUE in this region are rare and largely constrained to trees, which may bias estimates of iWUE trends toward more mesic, high elevation areas and neglect the responses of other key plant functional types such as shrubs that are dominant across much of the region. Here, we found evidence that iWUE is increasing in the Southwest at one of the fastest rates documented due to the recent drying trend. These increases were particularly large across three common shrub species, which had a greater iWUE sensitivity to aridity than Pinus ponderosa, a common tree species in the western United States. The sensitivity of both shrub and tree iWUE to variability in atmospheric aridity exceeded their sensitivity to increasing atmospheric [CO₂]. The shift to more water-efficient vegetation would be, all else being equal, a net positive for plant health. However, ongoing trends toward lower plant density, diminished growth, and increasing vegetation mortality across the Southwest indicate that this increase in iWUE is unlikely to offset the negative impacts of aridification.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.2118052118