Improved drought impacts detection with the novel implementation of plant hydraulics into an ecosystem model

Under future climate change, plants are expected to experience increased water stress. Most terrestrial biosphere models use empirical soil moisture stress factors to capture the impacts of droughts on stomatal conductance and photosynthesis. However, this empirical approach lacks a mechanistic representation of water flow in the soil-plant-atmosphere continuum (SPAC) and causes uncertainties in simulated carbon and water fluxes. In this study, a plant hydraulic module was developed and integrated into the process-based Biosphere-atmosphere Exchange Process Simulator (BEPS-EcoHydro). The plant hydraulic module considers three mechanisms of water uptake: water supply driven by the water potential gradient between soil and leaf, water demand due to potential transpiration, and water storage within the plant. Finally, the effect of water stress on photosynthesis is quantified via a linkage to leaf water potential. BEPS-EcoHydro and original BEPS were run to simulate water and carbon fluxes in a drought-prone temperate deciduous forest located in the Ozark region of central Missouri, USA, during 2005-2019. The results showed that BEPS-EcoHydro effectively captured variations in predawn leaf water potential at the ecosystem scale, and also outperformed the original BEPS in simulating soil moisture. Additionally, BEPS-EcoHydro performed better than the original model in simulating evapotranspiration (ET) and gross primary production (GPP), especially at the hourly scale. Importantly, BEPS-EcoHydro captured drought impact better than the original BEPS. These results suggest that consideration of plant hydraulics in process-based ecosystem models is needed to better understand vegetation responses to climate extremes.