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Revealing the hidden role of capacitance in the water flow through plants to the atmosphere.
  • Marcel Fuchs
Marcel Fuchs
Institute of Soil Water and Environmental Sciences

Corresponding Author:[email protected]

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Abstract

Identical physical principles dictate the formulation of transpiration and sap flow. Yet, a hiatus separates the ways the conduction of water in the vapor and liquid phases are dimensioned, leading to the elaboration of conflicting response mechanisms to water stress. An analysis prompted by the discrepancy between the dimensionality assigned to water vapor conductance for transpiration and that assigned to hydraulic conductance for sap flow reveals that capacitance combines with conductance to determine the respective transport rates. For transpiration, the capability of air to accept or release water vapor qualified as pneumatic capacitance, derived from theory, is equal to the reciprocal of the barometric pressure. The conductance is set by the network of diffusive and convective air paths where stomatal aperture is the ruling biological component. For sap flow the current view is that the proportionality between flux density and motive water potential difference is the hydraulic conductance, disregarding that its physical dimensions lump conductance and capacitance. Plant hydraulic capacitance derives from measured water retention curves. It varies according to water potential which is determined by the metabolic regulation of living cell osmolarity. Hydraulic conductance is set by abiotic factors: friction and water column cohesion in dead xylem conduits. Lumping the two properties into a single parameter erroneously defined as plant hydraulic conductance confounds the factors affecting sap flow, precluding a scientifically sound investigation of plant hydraulics.
13 Aug 2024Submitted to Plant, Cell & Environment
14 Aug 2024Submission Checks Completed
14 Aug 2024Assigned to Editor
14 Aug 2024Review(s) Completed, Editorial Evaluation Pending
14 Aug 2024Reviewer(s) Assigned
29 Sep 2024Editorial Decision: Revise Minor
14 Oct 20241st Revision Received
15 Oct 2024Submission Checks Completed
15 Oct 2024Assigned to Editor
16 Oct 2024Review(s) Completed, Editorial Evaluation Pending
16 Oct 2024Reviewer(s) Assigned