Linking stem diameter variations to sap flow, turgor and water potential in tomato

Water status plays an important role for fruit quality and quantity in tomato (Solanum lycopersicum L.). However, determination of the plant water status via measurements of sap flow (F-H2O) or stem diameter (D) cannot be done unambiguously since these variables are influenced by other effectors than the water status. We performed a semi-seasonal and a diurnal analysis of the simultaneous response of F-H2O and D to environmental conditions, which allowed us to distinguish different influences on Delta D such as plant age, fruit load and water status and to reveal close diurnal relationships between F-H2O and Delta D. In addition, an analysis of the diurnal mechanistic link between both variables was done by applying a slightly modified version of a water flow and storage model for trees. Tomato stems, in contrast with trees, seemed to maintain growth while transpiring because a large difference between turgor pressure (Psi(p)) and the yield threshold (Gamma) was maintained. Finally, the simultaneous response of D and F-H2O on irrigation events showed a possibility to detect water shortages