Isotopic offsets between bulk plant water and its sources are larger in cool and wet environments

Abstract. Isotope-based approaches to study plant water sources rely on the assumption that root uptake and within-plant transport are non-fractionating processes. However, a growing number of studies have reported offsets between source stable isotope composition for wide range ecosystems. These isotopic can result in erroneous attribution used by plants potential overestimations groundwater vegetation. We conducted global meta-analysis quantify magnitude these explored whether their variability could be explained either biotic or abiotic factors. Our database compiled 112 spanning arctic tropical biomes dual (?2H ?18O) (stem) water, including soil (sampled following various methodologies along variable depths). calculated 2H two ways: line conditioned excess (LC-excess) describes deviation from local meteoric (SW-excess) line, each sampling campaign within study. tested effects climate (air temperature content), class, traits (growth form, leaf habit, wood density, parenchyma fraction mycorrhizal habit) LC-excess SW-excess. Globally, stem was more depleted than (SW-excess < 0) 3.02±0.65 ‰ (P 0.05 according estimates our linear mixed model weighted sample size studies). In 95 % cases where SW-excess negative, indicating had not undergone evaporative enrichment (such as groundwater) unlikely explain observed soil–plant offsets. Soil class did any significant effect negative cold wet sites, whereas it positive warm sites. The climatic suggest methodological artefacts sole cause results would imply may lead inaccuracies when using bulk proxy infer sources.