Photosynthesis, vegetative habit and culinary properties of sage (Salvia officinalis) in response to low-light conditions

Abstract

Mapes, C. and Xu, Y. 2014. Photosynthesis, vegetative habit and culinary properties of sage (Salvia officinalis) in response to low-light conditions. Can. J. Plant Sci. 94: 881–889. Culinary sage (Salvia officinalis) is known to grow better at sunny locations with good drainage. However, when there is a necessity to propagate it in controlled environments with minimal additional lighting, or at shady locations, how significantly its growth and production would be restricted has not been well investigated. The objective of this study was to examine the responses of sage grown in a greenhouse over the winter when ambient light in the greenhouse is lower than 212 μmol m−2 s−1 (or a daily light integral of 9.2 mol m−2 d−1). Sage seedlings were planted in growing media and covered with various shade cloths to reach 70, 50 and 30% of the ambient irradiance. Photochemical efficiency and in situ chlorophyll status were estimated at 7, 21, and 56 d. The daily leaf emergence rate was calculated by monitoring changes in leaf number. Plant height, leaf size, biomass, aroma rating and soluble protein content of the sage plants grown under various light levels were measured at 84 d. The results indicate that light impacted the integrity of chloroplasts and the photosynthetic capacity of sage plants, as manifested by the lower the light level, the more the declines in variable fluorescence/maximal fluorescence and chlorophyll content index. Biochemical analysis revealed that the concentration of chlorophyll (per gram leaf dry mass) slightly increased under 50 and 30% light, but that of carotenoids was not changed. Light also affected the vegetative habit of sage plants. With reduced light intensity, plant height increased, whereas leaf size and number decreased. Double-blind aroma testing suggested that adequate light intesity might be required for the biosynthesis of essential oil in sage, attenuating its aroma. The soluble protein content in sage leaves declined at 50 and 30% light, suggesting a deminished source of essential amino acids contained in the plant. In summary, sage responds sensitively to reducing irradiance, which directly restricts its photosynthesis, and thus alters its vegetative growth and culinary properties.