A non-invasive probe for online-monitoring of turgor pressure changes under field conditions

An advanced non-invasive, field-suitable and inexpensive leaf patch clamp pressure probe for online-monitoring of the water relations of intact leaves is described. The probe measures the attenuated output patch clamp pressure, P_p, of a clamped leaf in response to an externally applied input pressure, P_clamp. P_clamp is generated magnetically. P_p is sensed by a pressure sensor integrated into the magnetic clamp. The magnitude of P_p depends on the transfer function, T_f, of the leaf cells. T_f consists of a turgor pressure-independent (related to the compression of the cuticle, cell walls and other structural elements) and a turgor pressure-dependent term. T_f is dimensionless and assumes values between 0 and 1. Theory shows that T_f is a power function of cell turgor pressure P_c. Concomitant P_p and P_c measurements on grapevines confirmed the relationship between T_f and P_c. P_p peaked if P_c approached zero and assumed low values if P_c reached maximum values. The novel probe was successfully tested on leaves of irrigated and non-irrigated grapevines under field conditions. Data show that slight changes in the microclimate and/or water supply (by irrigation or rain) are reflected very sensitively in P_p.