Where do crops take their water from? Using isotopic tracers in agricultural and agroforestry systems

Improving the efficiency and sustainability in water resources management in agricultural and agroforestry systems is becoming increasingly important in the light of the increasing pressure on agro-food production due to the growing world population growth and the changing climatic conditions. In this context, achieving an accurate quantification of the proportions of different water sources (including irrigation) taken up by plants has important ecological and economic implications for water saving and utilization. Stable isotopes of hydrogen and oxygen in the water molecule are powerful and, nowadays, affordable tracers that can greatly help to identify and quantify the seasonal water uptake patterns by plants. This tool is largely adopted in natural systems (e.g., in ecohydrological applications in forested environments) but has not been fully exploited in agricultural and agroforestry ecosystems. Here, we outline the advantages and limitations of this technique and report some examples on how it can support more traditional approaches to understand root water uptake dynamics in agricultural and agroforestry systems. Finally, we present a vision for future challenges and new research lines using isotope tracers to investigate crop water use.