Summary of the project: 'Resolving the mystery of

Summary of the project: ‘Resolving the mystery of deep roots: combining water stable isotopes with next generation technology – Isodrones’ A fundamental question for hydrologists and ecologists is how water moves through ecosystems and how and in which quantities water entering the system as precipitation becomes available for plants, replenishes soil and groundwater reservoirs or transforms into runoff. However, there are key aspects which are currently neither completely understood nor quantifiable related to the question how and from which reservoirs plants obtain their water from. One of those is the functioning of deep, potentially groundwater tapping roots. In addition to providing stability for the tree, the strategy of developing deep roots enables a plant to satisfy its water and nutrient demand when the supply from shallow soil water and precipitation are insufficient, which is of great importance during droughts and has implications for predicted climatic changes. Scientific research on deep roots is underrepresented and they are rarely considered in the management of water resources, mainly because of the difficulty to investigate them and a lack of quantitative methods. The overarching aim of this project is to develop a framework for quantifying the impact of deep roots on the water balance across different environments. Established and novel methodologies from multiple disciplines will be effectively combined in order to improve our understanding of the feedbacks between vegetation and their accessible water resources. Recent advances in stable water isotope techniques for quantitative studies along the soil-vegetation atmosphere interface are used in concert with novel opportunities arising from next generation drones (UAV-unmanned aerial vehicle) for highly resolute imagery and sample collection within the canopy in order to provide an integrated approach that incorporates above- and belowground techniques. Ultimately, these highly innovative approaches will help to improve our understanding of the functioning and adaptability of plants under different climatic conditions and enable a holistic evaluation of feedbacks between the vegetation and the hydrological cycle. We challenge current research gaps and shortcomings by developing a holistic framework for explaining why, how, and by which magnitude deep roots extract water from soils and groundwater. In addition, we utilize the ever-increasing technological opportunities effectively to improve current process-understanding. This combination of above- and belowground techniques might open a new avenue for ecohydrological research and alter the perception of the role of vegetation within the hydrological cycle.

Figure: Conceptualization of the project idea and main approaches. Both the vertical extent of the lateral root zone (blue highlights) as well as the maximum water uptake depth through tap roots (green highlights) are crucial parameters for understanding water movement at the soilvegetation-atmosphere interface. Methods need to be effectively combined from root-to-leave level as well as from top-to-bottom.