Hydraulic determinism as a constraint on the evolution of organisms and ecosystems

The interaction between plant hydraulics and plant structure was documented by Leonardo da Vinci, and its importance as a regulator of vegetation and ecosystem function remains of vital contemporary interest. It is proposed that hydraulics deterministically influence plant structure and function. This vision paper explores some aspects of the role of hydraulics in plant function, with a focus on the regulation of plant stomata and xylem water potentials, the morphology of branching networks in vines and trees, and the spatial organization of vegetation at landscape scales. Outstanding challenges include mechanistic and boundary condition descriptions of specific processes, the need to accommodate multiple spatial and temporal scales that do not lend themselves to statistical treatment and the self-referential nature of Darwinian evolution itself.