Cavitron extraction of xylem water suggests cryogenic extraction biases
vary across species but are independent of tree water stress
Abstract
Cryogenic vacuum distillation (CVD) is a widely used technique for
extracting plant water from stems for isotopic analysis, but concerns
about potential isotopic biases have emerged. Here, we leverage the
Cavitron centrifugation technique to extract xylem water and compare its
isotopic signature to that of CVD-extracted stem water as well as source
water. Conducted under field conditions in tropical northern Australia,
our study spans seven tree species naturally experiencing a range of
water stress levels. Our findings reveal a significant deuterium bias in
CVD-extracted bulk stem water when compared to xylem water (median bias \($-14.9\textperthousand$\)), whereas xylem water closely aligned with source water (median
offset \($-1.9\textperthousand$\)). We find substantial variations in deuterium bias among
the seven tree species (bias ranging from -19.3 to \($-9.1\textperthousand$\)), but
intriguingly, CVD-induced biases were unrelated to environmental factors
such as relative stem water content and pre-dawn leaf water potential.
These results imply that inter-specific differences may be driven by
anatomical traits rather than tree hydraulic functioning. Additionally,
our data highlight the potential to use a site-specific deuterium
offset, based on the isotopic signature of local source water, for
correcting CVD-induced biases.