Evidence for variations in cryogenic extraction deuterium biases of plant xylem water across foundational northeastern US trees

Abstract Measurements of oxygen and hydrogen isotopes in plant xylem water ( 2 H, 18 O) have helped to redefine conceptual and numerical models of the hydrological cycle and understand how plants compete for subsurface water. Recent experiments have shown that Cryogenic Vacuum Extraction (CVE) of plant xylem water can result in a δ 2 H bias. We tested if CVE δ 2 H‐biases varied significantly across seven foundational northeastern US forest trees with a series of tree core rehydration experiments. Our analysis demonstrated that CVE δ 2 H‐biases were well predicted by sample gravimetric water content and varied significantly with tree species identity. We show that species‐level δ 2 H‐bias corrections can result in substantially different understandings of plant water uptake and transpiration versus uncorrected data or generic bias corrections. This research demonstrates an urgent need for the critical evaluation of CVE for plant water extraction. In the absence of a stronger understanding of CVE δ 2 H‐biases, we recommend that xylem water δ 2 H observations should not be used in plant water uptake studies.