Growth, morphology, and photosynthetic activity of Chinese cabbage and lettuce grown under polyethylene and spectrum conversion films

The light environment affects the growth and morphology of vegetables grown in greenhouses. Although many studies have attempted to improve plant growth using spectrum conversion films (SCFs), their effects depend on the plant species, and the reasons are not clearly resolved. The objective of this study was to investigate the long-term effect of SCF on the growth, morphology, and photosynthetic activity of Chinese cabbage ( Brassica rapa L. ssp. pekinensis ) and romaine lettuce ( Lactuca sativa L. var. longifolia ) plants. SCF used in this study absorbed 14.8% of low photosynthetic efficiency wavelengths (500–600 nm) and emitted 14.4% of high photosynthetic efficiency (600–700 nm) wavelengths than polyethylene film (PE). The leaf optical properties, chlorophyll content, leaf nitrogen content, chlorophyll fluorescence parameters, and photosynthetic rate of two leafy vegetables grown under PE and SCF were compared at 20 or 25 days after transplanting. The electron transport rates of photosystems II and I and the photosynthetic rates of Chinese cabbage grown under SCF were significantly increased compared to those grown under PE. The leaf dry weight and leaf area of Chinese cabbage grown under SCF were also significantly increased by 33.0% and 33.3%, respectively, compared to those grown under PE. However, the lettuce grown under SCF showed no significant differences in photosynthetic activity, growth, or morphological characteristics compared to those grown under PE. We concluded that the solar spectrum modified by SCF could help increase photosynthetic efficiency and improve the yield of Chinese cabbage but not lettuce.