Effects of Irradiance Level on the Growth and Photosynthesis of Salvia

Abstract

Seedlings of Salvia coccinea, S. splendens and S. viridis were grown at 100, 50, 25 and 5% of full sunlight level to determine the influence of irradiance level on their grown and photosynthesis. For all species the shoot length and dry weight of wholeplant were decreased at 25% sunlight, but there was little defference in them between at 50 and 100% sunlight. Total leaf area tended to increase at 50% sunlight in S. splendens and S. viridis and to decrease at 25% sunlight in S.coccinea. Leaf area ratio increased with decreasing light intensity in every species, and the degree of increase was the least in S.coccinea. With decreasing light intensity, leaves became thinner and the specific leaf weight decreased for all species. Chlorophyll content and photosynthetic rate more decreased at 25% than those at 100 and 50% sunlight in S. splendens and S. viridis. There were little differences both in the chlorophyll content and photosynthesis among these light intensities in S.coccinea. This indicates that S.coccinea has higher adaptability to low irradiance than other two species. Under weak light condition the stomatal conductance increased for all species. At 5% sunlight, the plant dry weight was less than about 90% of that of 100% sunlight and photosynthetic rate almost decreased to the light compensation point.