Electrokinetic coupling coefficient for tree sap flow

Ascertain the value of the electrokinetic coupling coefficient C in the streaming-potential relation dV/dz = C · ∂p/∂z for tree sap flow within xylem channels, including its dependence on sap electrical conductivity, viscosity, zeta potential, and the wood–sap interface, in order to quantify electric fields generated by pressure gradients in trees.

Background

Spontaneous potential (SP) signals associated with fluid flow are modeled via an electrokinetic coupling coefficient C, typically characterized in rocks. The authors apply this framework to trees but indicate that tree-specific values of C are not established.

Their order-of-magnitude estimate suggests electric fields of the order of millivolts per meter would require C ≈ 10 V/Pa, which is significantly larger than values reported for rocks, motivating direct determination for trees.