Partial shade optimizes photosynthesis and growth in bayberry (Myrica rubra) trees

This study investigates the effects of radiation heat-load reduction under different shading conditions on the growth of three-year-old bayberry (Myrica rubra) trees from 1 July through 31 October 2007 in the Zhejiang Province, a warm subtropical region of China. The trees were grown under direct sunlight (control) and under 25%, 50%, and 75% shading conditions using black plastic nets. Stomatal conductance and photosynthesis were greatest under 50% shading, as were plant height and leaf and root dry weights. Twenty-five percent shading did not significantly influence plant height or root and leaf dry weights, whereas 75% shading resulted in a decrease in root and leaf dry weights when compared with the controls. The photochemical efficiency and electron transport of PSII increased under shaded conditions due to an increase in D1 protein. The concentrations of chlorophyll a and b and the total chlorophyll content in leaves were increased in plants grown under 25% and 50% shading, but reduced in those grown under 75% shading. Under 50% shading, growth and biomass increased due to increased photosynthesis, which resulted from decreased photodamage and increased chlorophyll concentration. These data show that 50% shading promotes optimal growth in bayberry plants.