A soil–plant–atmosphere continuum model reflecting the responses of plant hydraulic resistance to waterlogging

• A root water uptake model with waterlogging effects on root hydraulics was built. • The model effectively estimated plant hydraulic conductance and transpiration. • The model improved estimation accuracy, especially after prolonged waterlogging. • Transpiration was controlled by root hydraulics under moderate evaporative demand. In humid regions, intensive and intermittent precipitation has increased due to climate change, resulting in frequent waterlogging. Although waterlogging severely impedes the root hydraulic functions of a broad range of plant species, only a few studies have attempted mechanistic representation of plant responses to waterlogging. We hypothesized that incorporating plant hydraulic response to waterlogging into root water uptake model improves the estimation accuracy of water dynamics in humid regions. To test this hypothesis, we constructed two models: reference soil–plant–atmosphere continuum model, in which plant hydraulic resistance is constant, and a modified model (MM), in which plant hydraulic resistance increases with waterlogging. The performance of the models was tested using observed data of the soybean canopy cultivated in paddy field under humid climate. The MM accurately reproduced the increase in plant hydraulic resistance during the cultivation period. Modifying the model improved the estimation accuracy of the evapotranspiration rate and leaf water potential, especially on clear days after prolonged waterlogging. This performance improvement of MM was observed when evaporative demands exceeded 0.4 mm h −1 and was not dependent on soil water availability. An increase in plant hydraulic resistance due to soil waterlogging caused an imbalance between the atmospheric evaporative demand and the water uptake capacity of the roots, resulting in a midday depression in the evapotranspiration rate. These findings highlight that a process-based model incorporating the response of plant hydraulic resistance to waterlogging is useful for improving the understanding of water dynamics and leaf gas exchange in humid climates.