Stem Water Cryogenic Extraction Biases Estimation in Deuterium Isotope Composition of Plant Source Water.

Significance Stem xylem uptake and transport of plant source water is widely considered a critical component of the global water cycle. The deuterium signature of cryogenically extracted plant stem water (δ 2 H stem_CVD ) provides a useful means for studying water fluxes, but recent studies have shown uncertainty as to whether δ 2 H stem_CVD is a faithful reflection of true source water isotopic signal (δ 2 H source ). Here we confirm the common presence of significant deviations in δ 2 H stem_CVD from δ 2 H source in various plant species and demonstrate that this phenomenon is not caused by deuterium fractionation during root water uptake as traditionally thought, but rather is rooted in a cryogenic extraction-associated methodological artifact. Our findings may have wide-ranging implications for isotope-based ecohydrological and climate change studies.