Strong Solar Irradiance Reduces Growth and Alters Catechins Concentration in Tea Plants over Winter

Abstract

An experiment was conducted to investigate the effect of sunlight and chilling on growth, photosynthesis and chemical composition of tea plants growing in South Korea. The plants were grown in full sun (mid-day photosynthetic photon flux density, PPFD of 563 μmol-2s-1), slight shade (PPFD of 99 μmol-2s-1) or heavy shade (HS, PPFD of 5 μmol-2s-1) in a field at the foot of pine forest from October to March, 2012. Mean and minimum daily temperature fell below 0 °C in December and January. Shading had a small or no effect on shoot and leaf growth. Shading increased the concentration of chlorophyll compared with plants in full sun, with relatively stable values within a treatment over time. Shading increased chlorophyll fluorescence, with lower values in all treatments in late January. The concentration of total catechins was lower under shading, and lower in early January. Low temperatures appear to decrease chlorophyll fluorescence independently of light levels. Growth under heavy shade was dependently of stored reserves and would be unsustainable over the long term. Overall quality as reflected by the concentration of catechins was best under full sun conditions.