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Effect of light intensity and air velocity on the thermal exchange of indoor-cultured lettuce
Ahmed Hesham A.,Li Yangmei,Shao Lingzhi,Tong Yu-xin 한국원예학회 2022 Horticulture, Environment, and Biotechnology Vol.63 No.3
Heat and moisture transfer have a substantial influence on plant photosynthesis and productivity. Therefore, this study investigated the combined effect of light intensity (100, 200, and 300 μmol m−2 s−1) and air velocity (0.25, 0.50, and 0.75 m s−1) on the sensible heat flux (Sh), convection regime (CR), and latent heat flux (Lh) of lettuce plants grown in a plant factory with artificial light. The growth, photosynthetic rate, and occurrence of tipburn in lettuce plants were also evaluated. The effect of light intensity and air velocity on the thermal exchange of indoor-cultured lettuce was achieved through their combined effect on conductance to heat and mass transfer. Stomatal conductance was found to be strongly correlated with light intensity, with a correlation coefficient of 73%. The boundary layer conductance was highly correlated with air velocity, with a correlation coefficient of 96%. Accordingly, the Sh and Lh increased by 41.0% and 46.9%, respectively, with an increase in light intensity from 100 to 300 μmol m−2 s−1, and by 33.2% and 30.4%, respectively, with an increase in air velocity from 0.25 to 0.75 m s−1. Air velocity had a greater impact on CR, and forced convection was dominant between lettuce plants and the surrounding air. During the dark period, a decrease in stomatal conductance was accompanied by a decrease in Lh, particularly as air velocity increased. The photosynthetic rate and fresh weight of lettuce plants were strongly correlated with light intensity, and increased by 60.9% and 54.7%, respectively, as light intensity increased from 100 to 300 μmol m−2 s−1. However, the occurrence of tipburn in lettuce plants was significantly related to light intensity, and the highest number of lettuce leaves injured with tipburn of 5 leaves/plant was observed at a light intensity of 300 μmol m−2 s−1. When air velocity increased from 0.25 to 0.75 m s−1, the occurrence of tipburn decreased by 87.3%. Our results reveal that there was an obvious interaction between light intensity and air velocity on the thermal exchange, growth, and occurrence of tipburn in indoor-cultured lettuce. This study provides valuable insights into the combinational regulation of light intensity and air velocity for improving the growth and marketability of indoor-cultured lettuce.