Telling Tales of Water Journeys With Isotopic Tracers

Determining the sources of water inside plants using its isotopic composition is a long‐standing research challenge in ecohydrology. A better understanding of water sources can help improve models and ultimately contribute to more accurate forecasts of water availability, food production, carbon sequestration or ecosystem status. Over the years, several methods have been developed and applied to water source partitioning, and Gai et al. (2023, https://doi.org/10.1029/2022wr033849) provide a systematic assessment of the uncertainty of different isotopic tracers (2H, 3H, 17O, 18O) and mixing models (IsoSource, SIAR, MixSIR, MixSIAR) for an apple tree orchard on the Loess Plateau in north‐central China. For that study area, the combination of 2H and 18O with the MixSIAR mixing model is recommended. Importantly, the systematic assessment provides a framework that can be applied to select a suitable combination of tracers and mixing models for different ecosystems and climate zones. This commentary aims to provide a wider context for a selection of key results from Gai et al. (2023, https://doi.org/10.1029/2022wr033849) and highlight potential future research directions. Plain Language Summary Plants use water from the soil to survive, reproduce and grow. Plants can access water sources in shallow soil layers or from greater depth. The source of water can be determined by extracting water from a plant and measuring it precisely. This involves sophisticated machines and the use of models. Knowing where water is coming from, helps researchers to predict how plants respond to a changing climate or extreme weather. There exist several methods to estimate water sources and Gai et al. (2023, https://doi.org/10.1029/2022wr033849) test which of these methods works best for an apple tree orchard in China. This same procedure can be used for selecting the most appropriate method for other ecosystems and climate zones. Key Points The source of water inside plants, which can vary with season and across the field, can be traced using isotopes in water Gai et al. (2023, https://doi.org/10.1029/2022wr033849) present a systematic assessment of tracers and mixing models to partition water sources in vegetation Understanding water use strategies in vegetation can support modeling the response to extreme environmental conditions, such as droughts