Colored Plastic Film Mulching Regulates Light Quality and Sucrose Metabolism in Wine Grape in an Arid Desert Oasis

Light quality regulates plant morphogenesis and physiological processes. Colored plastic film mulching (CPFM) may be used to improve light quality and crop quality. Here, we investigated how different CPFMs regulate light quality and affect sucrose metabolism in wine grapes. Plastic film mulching with four color schemes was used as treatments: red (PMr), blue (PMb), red alternating with blue (PMrb), and silver (CK). Spectral distribution of sunlight was significantly affected by different CPFMs. PMr and PMb increased the proportion of red and blue light respectively while PMrb increased both red and blue light below plant canopy. Photosynthetic rate (Pn) was the highest in PMrb in all treatments caused by the highest contents of leaf photosynthetic pigments (Chl a, Chl b, and Chl a + b). The activities of both sucrose synthase and invertase (acid invertase and neutral invertase) in leaves were significantly increased in PMrb, which led to higher total soluble solids (TSS) and same level of reducing sugars (RS) relative to the CK treatment. In addition, the highest Chl a/b in PMrb maybe the other reason for the highest TSS in all treatments. Grape yields did not differ among treatments, but treatments exhibited a decreasing trend for TSS, RS, and sugar acid ratio in wine grapes in the order of: PMrb, PMr, CK, and PMb. Relative to monochrome plastic mulching, PMrb can be an efficient method to enhance light quality below plant canopy, thereby improving fruit carbohydrate contents and components by regulating leaf photosynthetic pigments and sucrose metabolism enzyme activities.