Abstract
The relationships between water potential and water content in plants
and soil have long been of interest, and there is increasing focus on
understanding how these fundamental measures are linked at larger
spatial and temporal scales. In this Perspective, we explore how the
theory of pressure-volume (PV) relationships can be applied at ecosystem
scale. We define and evaluate the concept and limitations of the
ecosystem and vegetation pressure-volume curves and discuss its
application using existing data. As a proof of concept, plot-scale
aboveground vegetation PV curves were generated from equilibrium (e.g.
predawn) water potentials and water content of the above ground biomass
of nine plots including tropical rainforest, savanna, temperate forest,
and a long-term Amazonian rainforest drought experiment. Initial
findings suggest high consistency among sites where the steady-state
water:biomass ratio is approximately 1:3, while the relative values of
ecosystem hydraulic capacitance and accessible water storage (the water
volume between saturation and a threshold) do not vary systematically
with biomass. The ecosystem-scale PV relationship provides a
thermodynamically consistent steady-state view of ecosystem form and
function and a biophysically robust basis for the interpretation of
remote sensing data of vegetation and soil water content, with promise
for revealing useful trends across ecosystems.