Cryogenic vacuum extraction bias misleads plant water source estimates: A correction framework based on soil properties

Study region A typical secondary forest in the East Asian monsoon region. Study focus Using an existing empirical correction method based on soil water content ( SWC ) and soil clay content ( SCC ), we corrected for the isotopic bias (Δδ) in soil water extracted via cryogenic vacuum extraction (CVE) and quantified the effects on dual-isotope relationships, line-conditioned excess (lc-excess), and inferred plant water source contributions. New hydrological insights These results highlighted the importance of accounting for soil properties when interpreting soil water isotope values (δ S ) in heterogeneous environments, advancing stable isotope applications in ecohydrological studies. The uncorrected δ S (δ uncorrected ) and corrected δ S (δ corrected ) differed significantly ( p < 0.01) in all soil layers, with SWC accounting for most of the variation in the estimated correction. The estimated CVE-driven Δδ could mimic isotopic patterns associated with non-equilibrium fractionation. The CVE-driven Δδ correction reduced this bias, increasing the average lc-excess values towards zero. Critically, the δ corrected data revealed plant water uptake patterns that differed from those inferred from the δ uncorrected data. Estimates based on the δ uncorrected data systematically overestimated water uptake from the surface soil layer, while those based on the δ corrected data indicated significant plant reliance on the intermediate layer ( p < 0.05). This reveals an adaptable plant drought-resistance strategy. Furthermore, the δ corrected refined the vertical isotopic stratification and improved the reliability of MixSIAR model outputs by narrowing confidence interval widths (CIWs) by 2.8–8.6% in surface and deep layers, highlighting the necessity of correcting CVE-driven Δδ to avoid ecological misinterpretation.