The Plant Water Pump

ongoing

With global warming, climate zones are projected to shift poleward, and the frequency and intensity of droughts to increase, driving threats to crop production and ecosystems. Plant hydraulic traits play major roles in coping with such droughts, and process-based plant hydraulics (water flowing along decreasing pressure or total water potential gradients) has newly been implemented in land surface models. An enigma reported for the past 35 years is the observation of water flowing along increasing water potential gradients across roots. By combining the most advanced modelling tool from the emerging field of plant micro-hydrology with pioneering cell solute mapping data, I found that the current paradigm of water flow across roots of all vascular plants is incomplete: it lacks the impact of solute concentration (and thus negative osmotic potential) gradients across living cells. This gradient acts as a water pump as it reduces water tension without loading solutes in plant vasculature (xylem). Importantly, water tension adjustments in roots may have large impacts in leaves due to the tension-cavitation feedback along stems. With The Plant Water Pump I will combine for the first time cutting-edge osmotic mapping and micro-hydrological modelling approaches to (1) characterize water status and osmotic responses to water deficit in diverse crop and tree species, (2) revolutionize the current paradigm of plant water uptake, and (3) increase the accuracy of plant water status functions for land surface models. By creating a continuum between key cell-scale variables and plant-scale water fluxes, this project lays the foundations for future multidisciplinary research encompassing plant physiology and ecohydrology. Besides its groundbreaking contribution to the fundamental understanding of plant water relations, this effort embodies a much-needed step toward the accurate forecasting of land water fluxes and decision support under future climates.