Growth, Photosynthesis, and Nutrient Uptake at Different Light Intensities and Temperatures in Lettuce

Light and temperature are two crucial factors affecting plant growth. Light intensities vary considerably with season and weather conditions. Reasonable light regulation at different temperatures is a key issue in environmental regulation. In this study, we determined the effects of light intensity and temperature on crop growth and development. Furthermore, we determined an optimal light value and a suitable light range at different temperatures for producing the lettuce Lactuca sativa L. Artificial climate chamber experiments were conducted at five light intensities (100, 200, 350, 500, and 600 mmol.m(-2).s(-1)), as well as at low (15 degrees C/10 degrees C), medium (23 degrees C/18 degrees C), and high (30 degrees C/25 degrees C) temperatures. In these experiments, we investigated the photosynthetic rate; chlorophyll fluorescence parameters; total N, P, and K uptake; and growth of lettuce plants. The results indicated that at a low temperature, the values of effective quantum yield of photosystem II photochemistry (Phi(PSII)), net photosynthetic rate (P-n), stomatal conductance (g(S)), and transpiration rate (T-r) -as well as those of N, K, and P uptake-were the highest at 350 mu mol.m(-2).s(-1), followed by 500 mu mol.m(-2).s(-1), which resulted in higher values for leaf number (LN), leaf area (LA), dry weight (DW), and fresh weight (FW). At the medium temperature, the values of Phi(PSII), P-n, g(S), and Tr, as well as those of N, K, and P uptake were higher at 350, 500, and 600 mu mol.m(-2).s(-1) than at other light intensities, resulting in high values for LN, LA, DW, and FW of lettuce plants. The LN, LA, and FW of lettuce plants were the highest at 500 mu mol.m(-2).s(-1), whereas DW was the highest at 600 mu mol.m(-2).s(-1). At a high temperature, lettuce plants exhibited the highest values of F-v/F-m, Phi(PSII), P-n, g(S), and Tr, as well as those of N, K, and P uptake for the 500 mmol.m(-2).s(-1) treatment; whereas LN, LA, FW, and DW were the highest at 600 mmol.m(-2).s(-1). In addition, the values of F-v/F-m indicated that lettuce plants were under stress under the following combinations: 600 mu mol.m(-2).s(-1) at the low temperature, 100 mu mol.m(-2).s(-1) at the medium temperature, and 100-350 mu mol.m(-2).s(-1) at the high temperature. Based on these results, an optimal regulation strategy for light intensity at different temperature environments was proposed for lettuce cultivars similar to L. sativa L. in some regions, such as the subtropical regions of China. Specifically, for low temperatures, light intensities of 350 to 500 mu mol.m(-2).s(-1)are recommended for production, and an intensity of 350 mu mol.m(-2).s(-1) provides optimal supplementary light during early spring and winter in greenhouses. For medium temperatures, light intensities of 350 to 600 mu mol.m(-2).s(-1) are recommended, and 500 mu mol.m(-2).s(-1) is the optimal value during the middle of spring and autumn. For high temperatures, light intensities of 500 to 600 mu mol.m(-2).s(-1)are recommended, and 600 mu mol.m(-2).s(-1) is the optimal value of light intensity during late spring and early autumn.