Sustainable crop production in greenhouses based on understanding crop physiology

More precise control of growth conditions has led to a strong increase in crop yield in greenhouses. To further improve crop production, product quality and sustainability, we need profound knowledge of the responses of plants to environmental conditions as well as crop management by growers (e.g., pruning and plant density). In young plants, rapid leaf formation initially boosts production through its role in intercepting light. However, we propose that many full-grown crops invest too much assimilate in new leaves. Responses of plants to the environment are seldom linear, and show many interactions. Furthermore, short- and long-term responses can be very different because of acclimation and feedback mechanisms. Therefore, research should not only study plant responses under constant conditions, but also analyse multiple interacting factors under fluctuating conditions. Controlling the climate should focus more on the microclimate near plant organs than on the average greenhouse climate. For instance, the temperature of the apical meristem may deviate by 4°C from that of the air. Leaf initiation rate depends on the temperature of the apical meristem, independent of the temperature of the other plant organs, and this has a significant impact on the plant phenotype. LED lamps open opportunities for energy saving while improving growth, yield and product quality, as they allow the instantaneous control of spectrum, intensity and direction of light, and the decoupling of lighting from heating. Effects of LED light on yield can be attributed to effects on leaf photosynthesis, plant morphology, which affects the absorption of light, and dry-matter partitioning. LED light can also trigger secondary metabolite production, resulting in increased disease resistance, or increased antioxidants such as vitamin C or anthocyanins. A next step in the control of the production process is indoor production without solar light in vertical farms. This step is boosted by developments in LED technology