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Abstract Rainfall amount and intensity are increasing under anthropogenic climate change, but many instrument records span less than a century. The oxygen isotopic composition of tree‐ring cellulose (δ18Ocell) reflects local source water, climate, and tree physiology. The patterns of δ18Ocellwithin tree‐rings has the potential to extend pre‐instrument climate records with subannual resolution, but the influences on intra‐ring δ18Ocellprofiles are unexplored in many settings. In this study, high‐resolution δ18Ocellprofiles were analyzed on three longleaf pine trees growing in a native savanna in Louisiana, United States. The time series covers a wide range of rainfall conditions from 2001 to 2008 C.E. with a total of 421 δ18Ocellanalyses. The δ18Ocellvalues for individual years are well correlated with each other both within and between trees (r = 0.71–0.78). We used principal components analysis andk‐means clustering to differentiate δ18Ocellprofiles into two groupings: symmetrical δ18Ocellprofiles versus asymmetrical profiles that have depressed latewood δ18Ocellvalues. The slope of latewood δ18Ocellprofiles and mean δ18Ocellvalues of latewood tissue correlate with total June‐November precipitation. We hypothesize that poorly drained soils in the study area mediate the influence of any individual storm event: in dry years,18O‐depleted signals from convective storms are moderated by subsequent evaporative enrichment of standing water, whereas in wet years, increased humidity and frequent re‐supply of18O‐depleted water overrides evaporative enrichment effects, resulting in low δ18Ocellof latewood. These results suggest that δ18Ocellproxies for tropical storm occurrence need to account for soil conditions at the site of tree growth.
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This content will become publicly available on April 1, 2026
Sub‐Daily Variations in Tree Xylem Water Isotopic Compositions in a Temperate Northeastern US Forest
ABSTRACT Sampling of stable isotopes in plant xylem water (δ2H, δ18O) has become a ubiquitous technique to study spatiotemporal variations in the water taken up by plant roots; however, open questions remain concerning the most appropriate time of day to sample trees to obtain representative xylem water isotopic values (δXYLEM). We sampled the δXYLEMof oak and maple trees prior to solar midday (i.e., in a recommended sampling window) and then again after solar midday (i.e., outside of the recommended window) across 4 months. The paired root mean squared difference between AM and PM δ18O ranged from 1.00‰ to 1.16‰ for maples and 0.23‰ to 2.55‰ for oaks across all sampling dates. Xylem water seasonal origin index (SOI) values derived from AM and PM δXYLEMsamples were significantly different, though both SOI estimates supported the conclusion that maple and oak δXYLEMreflected summer precipitation on all sampling dates. We conclude that sampling time of day is a significant consideration in the design of δXYLEMsampling campaigns; however, our findings also support flexibility in the collection time of δXYLEMin field sites where sampling during the optimal time of day is challenging.
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- Award ID(s):
- 2243263
- PAR ID:
- 10625673
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Hydrological Processes
- Volume:
- 39
- Issue:
- 4
- ISSN:
- 0885-6087
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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