Estimating fruit orchard stomatal conductance and transpiration under dynamic environments

Fruit tree growers perceive the need for decision making tools for their water management as they realize how such climate change and, more specifically, water scarcity is affecting the performance of their orchards. Furthermore, fruit trees, including olives, citrus and nuts have different hydraulic conductance, turgor loss points or fruit growth mechanisms which largely determine their response to environmental changes. Despite the multitude of models, estimating stomatal conductance and transpiration at the orchard level remains a challenge. In this study, we applied a direct parameterization of the Penman-Monteith equation developed to compute diurnal courses of orchard canopy conductance (gc) from sap flow in sub-hour resolution for both day and night conditions. We found that the model was sufficiently sensitive for detecting diurnal variation in gc and for predicting sap flow from environmental variables under various atmospheric evapotranspirative demands and differing levels of soil water availability. We used an extensive experimental data set of apple tree transpiration from 2011 in various sites ranging from very warm to temperate. The daily pattern of canopy conductance for water vapor provided by the model offers an unprecedented insight into rapid response to humidity of different cultivars as well as their light saturation levels. The model can be used to better understand the physiological (and productive) behavior of fruit tree crops in different environments, particularly in response to drought stress.