Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2005
Publication Date: 12/1/2005
Citation: Frantz, J., Bugbee, B. 2005. Acclimation of Plant Populations to Shade: Photosynthesis, Respiration, and Carbon Use Efficiency. Journal of the American Society for Horticultural Science. 130:918-927. Interpretive Summary: Changes in light are a common occurrence during the day and weeks of plant productivity, but surprisingly few studies have investigated the ability of whole plants and canopies to adapt to the changing light environment. Canopies of tomatoes and lettuce were shaded after they reached a point in growth where their leaves touched each other and none of the ground could be seen when viewing from the top. The shade remained on the canopies for up to 18 days. Photosynthesis, respiration, and the ratio between the two were measured using a 10-chamber CO2 gas-exchange system, which enabled us to monitor the short and long term growth effects on these plants. These parameters also let us grade the plants for acclimation to their new environment. At the lowest shade level (80% shade), lettuce never completely acclimated, whereas at the same shade level, tomatoes completely acclimated in 12 days. Both species photosynthesized more efficiently in lower light. Both species acclimated at a much slower rate than currently modeled. This work will improve the accuracy of models that predict yield in a variable light environment and help in understanding the role of stored reserves in environmental acclimation.
Technical Abstract: Surprisingly few studies have examined the rate and extent of plant acclimation to environmental changes on a whole plant or canopy basis. Reductions in photosynthetic photon flux (PPF) caused by clouds are particularly common. Canopies of tomato (Lycopersicon esculentum Mill.) and lettuce (Latuca sativa L.) were subjected to PPF reductions of up to 80% after canopy closure in a growth chamber. Whole plant photosynthesis, respiration, and carbon use efficiency (ratio of carbon gain to carbon fixed) were measured for 9 to 18 days after shade was applied. In contrast to widely used growth models, neither species immediately acclimated to the new environment. Lettuce grown in 80% shade never completely acclimated, as indicated by carbon use efficiency, whereas tomato acclimated after 12 days. Both species had more efficient photosynthesis (higher canopy quantum yield) after shade application. Tomato and lettuce were able to alter their growth and respiration in order to maintain carbon use efficiency, but acclimated at a much slower rate than currently modeled.