Transpiration is a crucial flux in greenhouses that directly affects plant growth. However, there are currently no direct measurements available. Sap flow is the most widely used method for quantifying transpiration, and calibration can enhance the accuracy of these estimates. Despite the existence of numerous recommendations for applying sap flow calibrations, few reports have employed them. Furthermore, plants frequently encounter various stressors during their growth and development, including drought, salinity, and reduced leaf area. These stressors can impede plant growth and, in extreme cases, can even result in plant death. Plant growth is contingent upon transpiration, and thus, stress conditions can also influence transpiration. However, there is a paucity of research on the effects of these stress conditions on transpiration.

The objective of this report is to calibrate the sap flow and subsequently investigate the effects of stresses, such as salinity, drought and leaf removal on transpiration in order to enhance irrigation strategies. Calibration was initially conducted by comparing daily sap flow with transpiration estimated by a water balance model using linear regression analysis. The corrected sap flow for the controlled and treated gutter was then compared to investigate the impact of stresses on transpiration.

The corrected sap flow coefficients were 2.30, 1.76, 1.64 and 3.58 for the controlled plants (1 and 2) and the treated plants (1 and 2), respectively. The corrected sap flow may be employed as an indicator of transpiration. It has been observed that salinity levels and a reduction in leaf area result in a decrease in transpiration, particularly when transpiration rates are already high. There was no significant difference in transpiration even when irrigation was reduced to 33% of the original amount. In the event of salinity, drought and leaf area reduction, it is recommended that the irrigation frequency be increased and the irrigation amount be reduced. Furthermore, it is recommended that salt leaching during the non-planting period be undertaken.

Water consumption reduction in greenhouse cultivation is a key objective for growers to optimize resource usage. Accurate estimation of transpiration, enabling growers to adapt water inputs to exact plant requirements, is vital for efficient water management. Various models have been developed to estimate transpiration. The Penman-Monteith and Stanghellini models are two of the most widely used models.
The Penman-Monteith model was originally designed for open-field conditions, while the Stanghellini model was specifically developed for greenhouse environments. In this study, the accuracy of these models in estimating transpiration was evaluated by comparing their estimated values with measured transpiration data. By affecting the VPD and stomatal resistance, temperature directly impacts the rate of transpiration in plants. This research also addresses a significant gap in previous studies by determining the optimal observation height for temperature data, which is essential for accurate modeling of transpiration.
Linear regression analysis was employed to assess the performances of the models. The results show that the Stanghellini model provides more precise estimations of transpiration compared to the Penman-Monteith model under greenhouse conditions. Moreover, using temperatures measured above the top of the plant canopy improves the accuracy of tran- spiration estimations in both models. Enhancing the accuracy of transpiration models in greenhouse conditions is critical for promoting efficient water management practices.