A New Framework to Identify Plant Water Sources

Scientists study different atoms of an element called stable isotopes as a powerful tool to understand how, and where plants take up and use water. The use of this tool assumes isotopic consistency, which is the relative abundance of the isotopes in water, during plant water uptake. Stable isotopes of water come from hydrogen and oxygen. In recent studies, scientists found significant differences in the hydrogen isotope values (δ2H) between plant water and their source waters. These differences, known as δ2H offsets, challenge the reliability of the isotopic method for research. Hydrogen isotope offset also complicates how scientists interpret plant-water interactions in ecosystems. In this project, researchers will develop a new way to identify the appropriate water pools from where plant water is sourced. The new tool will help scientists develop a clear method to accurately separate water pools that connect plants and soils. Using this new method, the researchers will clarify the causes of δ2H offsets and develop well-validated and standardized approaches for isotope-based ecohydrology research. Standardizing will improve data reliability, enable better comparison of global isotope databases, and advance our understanding of water and carbon cycles. The research will further train and mentor early-career researchers and students and create new datasets for communities that study plant and soil interactions. This project will systematically assess the fidelity and causes of observed δ2H offsets using a global data-synthesis approach. A new framework of the “Three Soil Water Worlds” concept and the “Two Plant Water Worlds” concept will be developed to account for water flow and corresponding isotope heterogeneities within the soil-vegetation-atmosphere continuum. Researchers expect to demonstrate that δ2H offsets do not occur if correct water pools are used in isotopic studies. To explicitly test this, a global re-quantification of δ2H offset measurements between plant water and their possible source waters will be performed. Both the new framework and the re-evaluated global δ2H offset datasets will significantly advance the robustness and reliability of isotopic methods in ecohydrological investigations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.