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This work is licensed under a Creative Commons Attribution 4.0 License.

Abstract

Stable carbon isotope ratios (δ13C) in tree rings have been widely used to study changes in intrinsic water-use efficiency (iWUE), sometimes with limited consideration of how C-isotope discrimination is affected by tree height and canopy position. Our goals were to quantify the relationships between tree size or tree microenvironment and wood δ13C for eight functionally diverse temperate tree species in northern New England, and to better understand the physical and physiological mechanisms underlying these differences. We collected short increment cores in closed-canopy stands and analyzed δ13C in the most recent 5 years of growth. We also sampled saplings in both shaded and sun-exposed environments. In closed-canopy stands, we found strong tree-size effects on δ13C, with 3.7 – 7.2‰ of difference explained by linear regression vs. height (0.11 – 0.28‰ m-1), which in some cases is substantially stronger than the effect reported in previous studies. However, open-grown saplings were often isotopically more similar to large codominant trees than to shade-grown saplings, indicating that light exposure contributes more to the physiological and isotopic differences between small and large trees than does height. We found that in closed-canopy forests, δ13C correlations with DBH were nonlinear but also strong, allowing a straightforward procedure to correct tree- or stand-scale δ13C-based iWUE chronologies for changing tree size. We demonstrate how to use such data to correct and interpret multi-decadal composite isotope chronologies in both shade-regenerated and open-grown tree cohorts, and we highlight the importance of understanding site history when interpreting δ13C time series.

Publication Date

4-2020

Journal Title

Tree Physiology

Publisher

Oxford University Press

Digital Object Identifier (DOI)

10.1093/treephys/tpz138

Grant/Award Number and Agency

National Science Foundation EAR-1562127; National Science Foundation DEB-1638688; New Hampshire Agricultural Experiment Station #1003450; Northeastern States Research Cooperative; Iola Hubbard Climate Change Endowment (UNH ESRC)

Document Type

Article

Comments

This is a pre-copyedited, author-produced version of an article accepted for publication in Tree Physiology following peer review. The version of record is available online at: https://dx.doi.org/10.1093/treephys/tpz138

Available for download on Sunday, January 24, 2021

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