Irradiance influences tea leaf (Camellia sinensis L.) photosynthesis and transpiration

Rates of net photosynthesis (P N) and transpiration (E), and leaf temperature (TL) of maintenance leaves of tea under plucking were affected by photosynthetic photon flux densities (PPFD) of 200-2 200 µmol m-2 s-1. P N gradually increased with the increase of PPFD from 200 to 1 200 µmol m-2 s-1 and thereafter sharply declined. Maximum P N was 13.95 µmol m-2 s-1 at 1 200 µmol m-2 s-1 PPFD. There was no significant variation of P N among PPFD at 1 400-1 800 µmol m-2 s-1. Significant drop of P N occurred at 2 000 µmol m-2 s-1. PPFD at 2 200 µmol m-2 s-1 reduced photosynthesis to 6.92 µmol m-2 s-1. PPFD had a strong correlation with TL and E. Both TL and E linearly increased from 200 to 2 200 µmol m-2 s-1 PPFD. TL and E were highly correlated. The optimum TL for maximum P N was 26.0 °C after which P N declined significantly. E had a positive correlation with P N.