Understanding the regulation of leaf and plant gas Exchange under water stress with a process-based model of stomatal conductance

Abstract

Water availability is one of the biggest constraints limiting the plant growth and species distribution around the world. This is the case in the Mediterranean region where, moreover, the frequency and amount of rainfall will decrease due to global warming. This will provoke longer periods of drought and a general decrease of water availability. In this context, one of the most vulnerable crops is grapevine. This crop has been traditionally rain-feed, although in recent years it’s becoming an irrigated crop. This increases the demand to regulate the water use by more precise irrigation techniques based on the plant water status. A good physiological indicator that allows knowing the plant water status is stomatal conductance. Although it is widely known the importance of the stoma, there is not an accurate model to predict their behavior as many physiological and environmental parameters co-regulate it. The aims of this thesis are to: a) study the physiological mechanisms regulating stomatal conductance, b) apply a process-based model to predict the behavior of stomatal conductance c) use this model as tool to better understand the physiological stomatal regulation along the canopy. Results show that stoma has a strong regulation by hydraulic conductance being a key physiological parameter regulating water use. In addition, abscisic acid and osmotic adjustment are also playing an important role in their regulation. On the other hand, the mechanistic model of stomatal conductance has been validated predicting with a good accuracy the variations throughout the day and season in well water and water stress conditions. At time, because this model is based on physiological parameters permits to infer about the relevance of those physiological parameters under water stress, predicting that hydraulic conductance has a main role on the regulation of stomatal conductance in different parts of the canopy.