EFFECTS OF WATERLOGGING ON THE GAS EXCHANGE, CHLOROPHYLL FLUORESCENCE AND WATER POTENTIAL OF QUERCUS VARIABILISAND PTEROCARYA STENOPTERA

Abstract

Cork oak (Quercus variabilis) and China wingnut (Pterocarya stenoptera) are important species in the subtropical riparian and drawdown areas of reservoirs and ponds in China. We investigated the effect of waterlogging on morphological and physiological characteristics of these species. We measured the maximum net photosynthesis rate (P_(max)), stomatal conductance (G_(s)), Chlafluorescence maximum quantum efficiency (F_(v)/F_(m)), chlorophyll content and water potential on different days during a period of waterlogging. Key Results Throughout a 70-day waterlogged period, the survival rates of seedlings of the two species were 100%. The earliest effects of waterlogging were significantly decreased P_(max), G_(s) andF_(v)/F_(m). On the 5th day of waterlogging, F_(v)/F_(m) of cork oak and China wingnut decreased to 0.694 and 0.757, respectively. On the 7th day, significant reduction of P_(max) (cork oak, 39% of control; China wingnut, 42%) and G_(s) (cork oak, 38.8% of control; China wingnut, 71.9%) were observed. With prolonged waterlogging, P_(max), G_(s) and F_(v)/F_(m) recovered gradually to control values in China wingnut, but not in cork oak where values decreased continuously. On the 70th day, P_(max) of cork oak was reduced by 94.1% of control and F_(v)/F_(m) was only 0.537.Waterlogged China wingnut seedlings developed hypertrophied lenticels and adventitious roots at their stem base and exhibited no visible symptoms of injury (neither mortality, leaf chlorosis, leaf necrosis, leaf abscission nor reduced chlorophyll content). However, cork oak showed leaf necrosis with waterlogging. The chlorophyll content of cork oak steadily declined from the 33rd day and the Chla/Chlb ratio also deceased. Predawn leaf water potential was higher in waterlogged cork oak seedlings compared to the control on the 10th and 70th days, but lower in waterlogged China wingnut seedlings. This indicated that water potential changes under waterlogging are species specific. All results show that cork oak exhibits damage to its photosynthetic apparatus under waterlogging. In contrast, although the photosynthetic apparatus of China wingnut is initially affected, it can recover, indicating that China wingnut seedlings can tolerate prolonged soil waterlogging better than cork oak seedlings. We conclude that it is more suitable to plant China wingnut in the drawdown areas of reservoirs and ponds than cork oak.