Ideas and perspectives: Tracing terrestrial ecosystem water fluxes using hydrogen and oxygen stable isotopes - Challenges and opportunities from an interdisciplinary perspective

In this commentary, we summarize and build upon discussions that emerged during the workshop Isotope-based studies of water partitioning and plant-soil interactions in forested and agricultural environments held in San Casciano in Val di Pesa, Italy, in September 2017. Quantifying and understanding how water cycles through the Earth's critical zone is important to provide society and policymakers with the scientific background to manage water resources sustainably, especially considering the ever-increasing worldwide concern about water scarcity. Stable isotopes of hydrogen and oxygen in water have proven to be a powerful tool for tracking water fluxes in the critical zone. However, both mechanistic complexities (e.g. mixing and fractionation processes, heterogeneity of natural systems) and methodological issues (e.g. lack of standard protocols to sample specific compartments, such as soil water and xylem water) limit the application of stable water isotopes in critical-zone science. In this commentary, we examine some of the opportunities and critical challenges of isotope-based ecohydrological applications and outline new perspectives focused on interdisciplinary research opportunities for this important tool in water and environmental science. © Author(s) 2018.The authors thank Marialaura Bancheri, Michele Bottazzi, Roman Cibulka, Massimo Esposito, Alba Gallo, Cesar D. Jimenez-Rodriguez, Angelika Kuebert, Ruth Magh, Stefania Mambelli, Alessia Nannoni, Paolo Nasta, Vladimir Rosko, Andrea Rücker, Noelia Saavedra Berlanga, Martin Šanda, and Anna Scaini for their contributions during the discussion at the workshop “Isotope-based studies of water partitioning and plant–soil interactions in forested and agricultural environments”. The authors also thank “Villa Montepaldi” and the University of Florence for the access to the workshop location, and the municipality of San Casciano in Val di Pesa for logistical support. The authors thank the Department of Innovation, Research and University of the Autonomous Province of Bozen/Bolzano for covering the Open Access publication costs. Last, but not least, the authors wish to thank Matthias Sprenger, Stephen Good, and J. Renée Brooks, as well as the Editor David R. Bowling, whose constructive reviews greatly improved this manuscript.Peer reviewe