Bassett Gundale, Kelley
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
Abstract
Triple oxygen isotope values of xylem water were measured along the length of smooth horsetail stems (Equisetum laevigatum). Extreme isotope enrichment is observed moving from base to stem tip. delta 18O values range from-8.3%o at the base to 82.6%o at the tip. Delta ' 17O values range from 0 to-1,797 per meg. The delta 18O and Delta ' 17O values are the most extreme measured for any terrestrial material and expand the known range of Delta ' 17O 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 theta k = 0.511 +/- 0.001. This new value is required to explain the low Delta ' 17O 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 1000ln18 alpha silica-water value at the plant base (35.89%o) appears to be in isotopic equilibrium, with far smaller fractionations of 10.3%o near the tip. The smaller fractionations at higher levels are explained by continual silica deposition as the plant elongates and the delta 18O values of each segment become higher. The overall integrated phytolith value is a combination of early and late silica growth. The Delta ' 17Osilica-Delta ' 17Owater values are not in equilibrium, explained by a kinetic isotope effect, with a lambda value of 0.5205 vs. 0.5244 for equilibrium. Phytolith isotope values may lead to erroneous interpretations for paleoclimate reconstruction.
Keywords
triple oxygen isotopes; extreme isotope fractionation; plant physiology; phytolith isotope chemistry; paleoclimatology
Published in
Proceedings of the National Academy of Sciences of the United States of America
2025, volume: 122, number: 44, article number: e2507455122
SLU Authors
UKÄ Subject classification
Geochemistry
Publication identifier
- DOI: https://doi.org/10.1073/pnas.2507455122
Permanent link to this page (URI)
https://res.slu.se/id/publ/144634