Effect of soil water stress on photosynthetic light response curve of tea plant (Camellia sinensis)

Two yearold seedlings of tea plants (Camellia sinensis cv. Tieguanyin and C.sinensis cv. Fudingdabaicha ) were cultivated in a pot experiment to investigate the photosynthetic parameters with light intensity of PAR 0 ～ 2 000 μmol·m^-2·s^-1 under four water stress treatments: 75% (normal water supply), 55% (slight water stress), 35% (mild water stress) and 20% (severe water stress) of soil field capacity. The results show that light response curves of net photosynthetic rate (Pn ) in “Tieguanyin” and “Fudingdabaicha” tea plants follow an exponential equation model. Under normal water supply condition, “Tieguanyin” and “Fudingdabaicha” maximum net photosynthetic rates (Pn_max) are 8.169 μmol(CO₂)·m^-2·s^-1 and 3.946 μmol(CO₂)·m^-2·s^-1; apparent quantum yields (AQY ) are 0.039 μmol(CO₂)·μmol^-1 and 0.024 μmol(CO₂)·μmol^-1; light saturation points (LSP ) are 973.07 μmol·m^-2·s^-1 and 775.78 μmol·m^-2·s^-1; light compensation points (LCP ) are 5.15 μmol·m^-2·s^-1 and 6.49 μmol·m^-2·s^-1; and dark respiration rates (Rd ) are 1.025 μmol(CO₂)·m^-2·s^-1 and 1.040 μmol(CO₂)·m^-2·s^-1 respectively. Under soil drought stress, Pn_max, AQY and LSP decrease while LCP and Rd increase. Compared with “Fudingdabaicha”, “Tieguanyin” presents higher Pn,Pn_max, LSP and AQY, but lower LCP andRd ; indicating that “Tieguanyin” has higher adaptation capacity to different soil water supply and light intensity than “Fudingdabaicha” under the same environmental conditions.