Browsing by Author "Cernusak, Lucas A."

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    Do 2H and 18O in leaf water reflect environmental drivers differently?
    (Wiley, 2022) Cernusak, Lucas A.; Barbeta, Adrià; Bush, Rosemary T.; Eichstaedt (Bögelein), Rebekka; Ferrio, Juan Pedro; Flanagan, Lawrence B.; Gessler, Arthur; Martín-Gómez, Paula; Hirl, Regina T.; Kahmen, Ansgar; Keitel, Claudia; Lai, Chun-Ta; Munksgaard, Niels C.; Nelson, Daniel B.; Ogée, Jérôme; Roden, John S.; Schnyder, Hans; Voelker, Steven L.; Wang, Lixin; Stuart-Williams, Hilary; Wingate, Lisa; Yu, Wusheng; Zhao, Liangju; Cuntz, Matthias; Earth Sciences, School of Science
    We compiled hydrogen and oxygen stable isotope compositions (δ2H and δ18O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ2H was more closely correlated with δ2H of xylem water or atmospheric vapour, whereas leaf water δ18O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ2H of meteoric waters relative to the extent of leaf water evaporative enrichment compared to δ18O. We next expressed leaf water as isotopic enrichment above xylem water (Δ2H and Δ18O) to remove the impact of xylem water isotopic variation. For Δ2H, leaf water still correlated with atmospheric vapour, whereas Δ18O showed no such correlation. This was explained by covariance between air relative humidity and the Δ18O of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that 2H and 18O in leaf water do indeed reflect the balance of environmental drivers differently; our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water.
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    The determining factors of hydrogen isotope offsets between plants and their source waters
    (Wiley, 2024-03) Zhao, Liangju; Liu, Xiaohong; Wang, Ninglian; Barbeta, Adrià; Zhang, Yu; Cernusak, Lucas A.; Wang, Lixin; Earth and Environmental Sciences, School of Science
    A fundamental assumption when using hydrogen and oxygen stable isotopes to understand ecohydrological processes is that no isotope fractionation occurs during plant water uptake/transport/redistribution. A growing body of evidence has indicated that hydrogen isotope fractionation occurs in certain environments or for certain plant species. However, whether the plant water source hydrogen isotope offset (δ2H offset) is a common phenomenon and how it varies among different climates and plant functional types remains unclear. Here, we demonstrated the presence of positive, negative, and zero offsets based on extensive observations of 12 plant species of 635 paired stable isotopic compositions along a strong climate gradient within an inland river basin. Both temperature and relative humidity affected δ2H offsets. In cool and moist environments, temperature mainly affected δ2H offsets negatively due to its role in physiological activity. In warm and dry environments, relative humidity mainly affected δ2H offsets, likely by impacting plant leaf stomatal conductance. These δ2H offsets also showed substantial linkages with leaf water 18O enrichment, an indicator of transpiration and evaporative demand. Further studies focusing on the ecophysiological and biochemical understanding of plant δ2H dynamics under specific environments are essential for understanding regional ecohydrological processes and for conducting paleoclimate reconstructions.