Responses of Leaf Gas Exchanges, Chlorophyll a Fluorescence, and Fruit Yield and Quality of Greenhouse Tomatoes to Shading with Retractable Liquid Foam

Greenhouse air temperature is usually very high during the summer, which could cause significant damage to plants. Shading during this period may help to decrease incoming heat and improve plant microclimate, benefiting leaf gas exchanges, plant growth and productivity. Sunarc of Canada has developed a new technology that generates and distributes retractable liquid foam between the two layers of polyethylene films used as greenhouse covering material. Control and prototype greenhouses equipped with the Sunarc technology were used to investigate the effects of shading with liquid foam on the leaf gas exchanges, Chl a fluorescence, fruit yield and quality of tomatoes (Lycopersicon esculentum). The foam was applied during the daytime to provide different levels of shading. Several experiments were conducted to evaluate various shading strategies: 1) comparing the conventional shading curtain to the liquid foam shading system; 2) applying the foam shading only based on outside solar radiation and 3) applying foam shading based on both the outside solar radiation and greenhouse air temperature. Our results showed that on very hot summer days, the use of liquid foam for shading (40% to 65% shading) improved greenhouse microclimate (reduced air temperature by 2 degrees C to 6 degrees C and increased relative humidity by 5% to 12%). Also, fruit size was increased and percentage of unmarketable fruit (cracking and blossom-end-rot) was reduced with liquid foam shading.