Effect of stem age on the response of stem diameter variations to plant water status in tomato

Plant water status plays a major role in glasshouse cultivation of tomato (Solanum lycopersicum L.). New climate control technologies alter the glasshouse climate and make it less dependent on solar radiation. However, irrigation strategies are still often based on solar radiation sums. In order to maintain a good plant water status, it is interesting to use plant-based methods such as monitoring sap flow (F) or stem diameter variations (SDV). Though SDV give important information about plant water status, an unambiguous interpretation might be difficult because other factors such as stem age, fruit load and sugar content of the stem also affect SDV. In this study, an analysis of the effect of stem age on the response of SDV to water status was performed by calibration of a mechanistic flow and storage model. This allowed us to determine how parameter values changed across the growing season. Tissue extensibility decreased over the growing season resulting in a lower growth rate potential, whereas daily cycles of shrinking and swelling of the stem became more pronounced towards the end of the growing season. Parameters were then adapted to time-dependent variables and implemented in the model, allowing long term simulation and interpretation of SDV. Sensitivity analysis showed that model predictions were very sensitive to initial sucrose content of the phloem tissue and the parameters related to plastic growth

Model-assisted analysis of elevated temperature and vapour pressure deficit effects on tomato stem and fruit water balance

Maintaining good plant water status is crucial for optimal production and quality of tomato in greenhouses. Various new climate control technologies have been introduced to make greenhouse cultivation more energy-efficient, resulting in a modified greenhouse climate. Recently, there has been growing interest in the use of plant-based methods to steer the climate. Monitoring stem diameter variations (SDV) has been extensively studied in tree species, but is also very promising for herbaceous crops. Stem and fruit diameter variations provide crucial information about plant water status, though unambiguous interpretation of these dynamics is often difficult. Mechanistic modelling can help to elucidate the mechanisms driving plant behaviour and is therefore an important tool for interpreting the dynamic response of the plants to changes in microclimate. In the present study, tomato plants (Solanum lycopersicum L.) were subjected to elevated air temperature (Ta) and vapour pressure deficit (VPD), while SDV, sap flow and fruit growth were continuously monitored. Results indicated that stem shrinkage became more pronounced and fruits shrank during periods of high Ta and VPD. Simulation results showed that reduced fruit growth resulted from both increased fruit transpiration and decreased phloem inflow. Moreover, xylem backflow appeared when Ta and VPD reached maximum values. It was demonstrated that the reduced fruit growth resulted mainly from changes in stem water potential, rather than fruit water potential