Abstract: To explore the photosynthetic physiological responses of Phyllostachys heteroclada, a waterlogging-tolerant and fast-growing bamboo species, to different degrees of waterlogging stress, we measured the photosynthetic gas exchange parameters, photosynthetic pigments and leaf resource use efficiency of one-year-old P. heteroclada to the degree of waterlogging stress and duration of waterlogging under three treatments: normal watering (as control), half flooding, and full flooding. After waterlogging for three days, net photosynthetic rate, light saturation point and transpiration rate of P. heteroclada under half flooding increased significantly compared with the control, but there was no change under full flooding. With the extension of stress duration, all the variables decreased, with the decreasing range being positively correlated with the degree of stress. After waterlogging for six days, stomatal conductance of P. heteroclada leaves was significantly higher than that of the control, and then showed a downward trend. The intercellular CO₂ concentration showed a trend of decreasing first and then increasing, and the difference with the control was not significant by day 9. The recovery time was positively correlated with the degree of stress. Dark respiration rate and light compensation point increased with increasing stress duration. The content of total photosynthetic pigments showed a trend of decreasing first and then increasing with the duration of stress. The ratio of chlorophyll to carotenoid remained at 3∶1, while the ratio of chlorophyll a to chlorophyll b decreased from 3∶1 to 2∶1. Leaf water  use efficiency showed a trend of decreasing and then increasing. Both the apparent energy utilization rate and apparent CO₂ utilization rate showed a decreasing trend, and their decreasing rate gradually decreased with the extension of waterlogging duration. Our results indicated that photosynthesis of bamboo showed certain promoted effects under half flooding stress. With the extension of stress duration, the photosynthetic parameters gradually decreased to stable levels, and bamboo showed certain waterlogging tolerance by adjusting the ratio of photosynthetic pigments and improving water use efficiency. After adapting to the flooded environment, photosynthetic pigments began to recover.

Key words: waterlogging, Phyllostachys heteroclada, photosynthetic pigment, photosynthetic parameter