Technical note: On uncertainties in plant water isotopic composition following extraction by cryogenic vacuum distillation

Abstract. Recent studies have challenged the interpretation of plant water isotopes obtained through cryogenic vacuum distillation (CVD) based on observations a large 2H fractionation. These hypothesized existence an H-atom exchange between and organic tissue during CVD extraction with magnitude H related to relative content sample; however, clear evidence is lacking. Here, we systematically tested uncertainties in isotopic composition CVD-extracted by conducting series incubation rehydration experiments using isotopically depleted water, at natural isotope abundance, woody materials exchangeable H, without (cellulose triacetate caffeine). We show that offsets hydrogen oxygen ratios expected reference values (Δ2H Δ18O) inversely proportional relationships absolute amount being extracted, i.e. lower amount, higher Δ2H Δ18O. However, neither nor Δ18O values, were sample content. The pattern was more pronounced for atoms than non-exchangeable atoms. This caused combined effect enrichments evaporation sublimation depend amount. itself negligible. Despite these technical issues, observed amount-dependent patterns much less samples abundance particularly low when sufficiently high amounts extracted (>600 µL). Our study provides new insights into mechanisms causing fractionation water. methodological can be controlled if are used ecohydrological studies.