Extreme triple oxygen isotope fractionation in <i>Equisetum</i>

Triple oxygen isotope values of xylem water were measured along the length of smooth horsetail stems (<i>Equisetum laevigatum</i>). Extreme isotope enrichment is observed moving from base to stem tip. δ<sup>18</sup>O values range from -8.3‰ at the base to 82.6‰ at the tip. Δ'<sup>17</sup>O values range from 0 to -1,797 per meg. The δ<sup>18</sup>O and Δ'<sup>17</sup>O values are the most extreme measured for any terrestrial material and expand the known range of Δ'<sup>17</sup>O values by fivefold for mass-dependent fractionation on Earth. The extreme isotope enrichments are explained using a hybrid evaporation/chain-of-lakes model, allowing us to refine the leaf respiration coefficient to θ<sub>k</sub> = 0.511 ± 0.001. This new value is required to explain the low Δ'<sup>17</sup>O values previously measured in desert plants and animals and is critical when using fossil samples for paleoclimate reconstruction. Coexisting phytoliths and stem water were also measured. The 1000<i>ln</i><sup>18</sup>α<sub>silica-water</sub> value at the plant base (35.89‰) appears to be in isotopic equilibrium, with far smaller fractionations of 10.3‰ near the tip. The smaller fractionations at higher levels are explained by continual silica deposition as the plant elongates and the δ<sup>18</sup>O values of each segment become higher. The overall integrated phytolith value is a combination of early and late silica growth. The Δ'<sup>17</sup>O<sub>silica</sub> - Δ'<sup>17</sup>O<sub>water</sub> values are not in equilibrium, explained by a kinetic isotope effect, with a λ value of 0.5205 vs. 0.5244 for equilibrium. Phytolith isotope values may lead to erroneous interpretations for paleoclimate reconstruction.

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Proceedings of the National Academy of Sciences
Published
2025-10-28
DOI
https://doi.org/10.1073/pnas.2507455122
Primary Topic
Silicon Effects in Agriculture
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article
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article

Extreme triple oxygen isotope fractionation in Equisetum

K. M. Holland, Paula J. Rudall, A. Gargano, Vincent Hare et al.
Proceedings of the National Academy of Sciences
Silicon Effects in Agriculture
article

Extreme triple oxygen isotope fractionation in Equisetum

K. M. Holland, Paula J. Rudall, A. Gargano, Vincent Hare, Thure E. Cerling, Jarunetr Sae-Lim, Teresa Dominguez, Jensen Wainwright, Z. D. Sharp, Elena Stiles, Charles G. Knutson, E. J. Cano, Jessica Johnson, Payal Banerjee, James R. Ehleringer, Dalton Bryant, Catherine Peshek, Jordan A.G. Wostbrock, Kelley R. Bassett, C. Gagnon, Eduardo Di Marcantonio, Lauren Hartzell, Michael H. Dowd, Maxwell Horsford, Paul Botté
article en

Abstract

Triple oxygen isotope values of xylem water were measured along the length of smooth horsetail stems (<i>Equisetum laevigatum</i>). Extreme isotope enrichment is observed moving from base to stem tip. δ<sup>18</sup>O values range from -8.3‰ at the base to 82.6‰ at the tip. Δ'<sup>17</sup>O values range from 0 to -1,797 per meg. The δ<sup>18</sup>O and Δ'<sup>17</sup>O values are the most extreme measured for any terrestrial material and expand the known range of Δ'<sup>17</sup>O values by fivefold for mass-dependent fractionation on Earth. The extreme isotope enrichments are explained using a hybrid evaporation/chain-of-lakes model, allowing us to refine the leaf respiration coefficient to θ<sub>k</sub> = 0.511 ± 0.001. This new value is required to explain the low Δ'<sup>17</sup>O values previously measured in desert plants and animals and is critical when using fossil samples for paleoclimate reconstruction. Coexisting phytoliths and stem water were also measured. The 1000<i>ln</i><sup>18</sup>α<sub>silica-water</sub> value at the plant base (35.89‰) appears to be in isotopic equilibrium, with far smaller fractionations of 10.3‰ near the tip. The smaller fractionations at higher levels are explained by continual silica deposition as the plant elongates and the δ<sup>18</sup>O values of each segment become higher. The overall integrated phytolith value is a combination of early and late silica growth. The Δ'<sup>17</sup>O<sub>silica</sub> - Δ'<sup>17</sup>O<sub>water</sub> values are not in equilibrium, explained by a kinetic isotope effect, with a λ value of 0.5205 vs. 0.5244 for equilibrium. Phytolith isotope values may lead to erroneous interpretations for paleoclimate reconstruction.

Proceedings of the National Academy of SciencesVol. 122(44)
Purchase College (US), University of Hawaiʻi at Mānoa (US), Roma Tre University (IT), Planetary Science Institute (US), University of Alberta (CA), SUNY College of Environmental Science and Forestry (US), University of Cape Town (ZA), University of New Mexico (US), University of Alabama (US), University of Oregon (US), University of California, Santa Cruz (US), University of Washington (US), University of California, Irvine (US), University of Utah (US), Brown University (US), Royal Botanic Gardens, Kew (GB), Swedish University of Agricultural Sciences (SE), Centre de Recherche et d’Enseignement de Géosciences de l’Environnement (FR), Planetary Systems (United States) (US), Scientific Centre for Aerospace Research of the Earth (UA), Irvine University (US), Geological Survey of Alabama (US), Department of Earth Sciences (RU), Lunar and Planetary Institute (US)
Openalex Percentile: Top 77%
Silicon Effects in Agriculture
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