A soil-plant-atmosphere continuum (SPAC) model for simulating tree transpiration with a soil multi-compartment solution

[Aims] A soil-plant-atmosphere continuum (SPAC) model for simulating tree transpiration (Ep) with variable water stress and water distribution in the soil is presented. The model couples a sun/shade approach for the canopy with a discrete representation of the soil in different layers and compartments.[Methods] To test its performance, the outputs from the simulations are compared to those from an experiment using trees of olive ‘Picual’ and almond ‘Marinada’ with the root system split into two. Trees are subjected to different irrigation phases in which one side of the root system is dried out while the other is kept wet.[Results] The model is able to accurately predict Ep (R2 and the efficiency factor (EF) around 0.9) in the two species studied. The use of a function that modulates the uptake capacity of a root according to the soil water content was necessary to track the fluxes observed from each split part. It was also appropriate to account for root clumping to match the measured and modelled leaf water potential.[Conclusions] Coupling the sun/shade approach with the soil multi-compartment solution provides a useful tool to explore tree Ep for different degrees of water availability and distribution.This work was supported by project AGL-2010-20766 of the Spanish Ministry of Economy and Competitiveness (former Ministry of Science and Innovation) and by the European Community’s Seven Framework Programme-FP7 (KBBE.2013.1.4-09) under Grant Agreement No. 613817 (MODEXTREME, modextreme.org). The authors wish to thank both the “FPI” programme of the aforementioned ministry and the JAE programme of the Spanish Research Council (CSIC) for providing the Ph.D. scholarships granted to the first and the second author, respectively.Peer reviewe