Leaf boundary layer conductance in ventilated greenhouses: An experimental approach

Improving the design, control and management of greenhouse ventilation systems requires a better insight into the coupling and feedback mechanisms between the crop, the internal atmosphere and the outside atmosphere. The objective of this work was to characterize the leaf boundary-layer conductance (gb) in highly ventilated greenhouse conditions and to study its dependence on the ventilation conductance (gv) and outside conditions. For this purpose, measurements of gb were carried out in a greenhouse cultivated with rose plants, using rose leaf replicas consisting of a pair of artificial leaves, one being heated and the other unheated. The relation between gb and gv was established and quantified, and further generalised to the case of large greenhouses. By implementing the relation into the expression of the canopy aerodynamic conductance, the influence of the leaf area index (LAI) on the total greenhouse conductance was addressed. It was shown that LAI plays a major role in determining the degree of coupling between the greenhouse canopy and the outside atmosphere. The results underline the importance of integrating estimates of the canopy aerodynamic conductance in greenhouse climate control algorithms.