Characterizing the Light Environment within Greenhouse Vegetable Crops
Citation
Terlizzese, D., Zheng, Y., and Hao, X. 2022. Characterizing the Light Environment within Greenhouse Vegetable Crops, Canadian Greenhouse Conference, Oct. 5-6, 2022, Niagara Falls, ON, Canada
Résumé en langage clair
To effectively manage a greenhouse crop’s production, it is essential to understand the natural light environment and the plants’ physiological responses to light. This study investigated the dynamics of photosynthetic photon flux densities (PPFD) and light quality within the canopies of greenhouse-grown eggplant (Solanum melongena) and the photosynthetic capacities of leaves at different locations within the canopies. The light environment was quantified at 0.2 m intervals within (intra-canopy) and adjacent to (extra-canopy) the crop canopy, on both sunny and cloudy days within a commercial greenhouse located in Leamington, Ontario, Canada. Our results indicated a linear decline in extra-canopy PPFD on both sunny and cloudy days, but an exponential decrease in intra-canopy PPFD. The intra-canopy PPFD decreased by 91% and 76% between 0 m to 0.4 m from the canopy apex on sunny and cloudy days respectively. The lower canopy (0.6-1.2 m) light spectrum consisted largely of far-red light, equal amounts of red and green light, with a lower percentage of blue light. Parameters derived from leaf-level light response curves indicated that light-saturated net carbon exchange rate, light saturation point, and light compensation point decreased as the distance from canopy apex increased, while quantum yield was unaffected. Thus, leaves in the lower canopy were less efficient at utilizing high PPFD but displayed no deterioration of photosynthetic machinery. Based solely on photosynthetic capabilities, leaves between 0-1.0 m from the canopy apex should not be removed in greenhouse eggplant production.
Résumé
To effectively manage a greenhouse crop’s production, it is essential to understand the natural light environment and the plants’ physiological responses to light. This study investigated the dynamics of photosynthetic photon flux densities (PPFD) and light quality within the canopies of greenhouse-grown eggplant (Solanum melongena) and the photosynthetic capacities of leaves at different locations within the canopies. The light environment was quantified at 0.2 m intervals within (intra-canopy) and adjacent to (extra-canopy) the crop canopy, on both sunny and cloudy days within a commercial greenhouse located in Leamington, Ontario, Canada. Our results indicated a linear decline in extra-canopy PPFD on both sunny and cloudy days, but an exponential decrease in intra-canopy PPFD. The intra-canopy PPFD decreased by 91% and 76% between 0 m to 0.4 m from the canopy apex on sunny and cloudy days respectively. The lower canopy (0.6-1.2 m) light spectrum consisted largely of far-red light, equal amounts of red and green light, with a lower percentage of blue light. Parameters derived from leaf-level light response curves indicated that light-saturated net carbon exchange rate, light saturation point, and light compensation point decreased as the distance from canopy apex increased, while quantum yield was unaffected. Thus, leaves in the lower canopy were less efficient at utilizing high PPFD but displayed no deterioration of photosynthetic machinery. Based solely on photosynthetic capabilities, leaves between 0-1.0 m from the canopy apex should not be removed to decrease total plant sink strength.