Leaf boundary layer conductance in a tomato canopy under the convective effect of circulating fans in a greenhouse heated by an air duct heater

The optimal design of air currents in greenhouses primarily requires a better insight into convective exchange between leaves and the environment via the leaf boundary layer. The objectives of this study were to establish a method for continuous and multipoint determination of leaf boundary layer conductance (G_A) in a tomato canopy within a greenhouse, and to evaluate the convective effect of circulating fans on the air currents in the tomato canopy based on vertical and horizontal profiles of G_A. The operation of circulating fans changed the direction and velocity of air currents by mixing the air in the greenhouse, which reduced vertical differences of air temperature in the tomato canopy. Furthermore, convective exchange between leaves and the environment was significantly enhanced via increases in G_A. However, the vertical and horizontal distributions of G_A were dependent on the locations of the circulating fans. In particular, the circulating fans set above the canopy resulted in remarkably higher G_A in the upper canopy. This approach to profiling the spatial distribution of G_A can contribute to the optimal design of air currents for efficient environmental control in greenhouses.