Biological constraints on water transport in the soil-plant-atmosphere system

► Transpiration is described over two separate time scales. ► At sub-hourly to growing season, plant hydraulic traits are stationary. ► At these scales, water fluxes are described by nonlinear diffusion equations. ► At inter-annual scales, these traits change due to ontogeny and species shifts. ► At these scales, trait changes are coordinated to optimally use water.