Endodormancy induction and photosynthetic physiology of Myricaria laxiflora remnant populations under chronic summer submersion

Abstract

Dormancy is a protective survival strategy developed by plants to face chronic, seasonal and severe abiotic stress. In this study, changes in photosynthetic indices were measured during different periods of summer dormancy in the rare and endangered plant Myricaria laxiflora to reveal the adaptation to summer flooding. Results showed that the photosynthetic activity of M. laxiflora remnant populations gradually decreased with the onset of summer dormancy. The net photosynthetic rate, rate of transpiration, and stomatal conductance continued to decrease as dormancy progressed, whereas the intercellular CO2 concentration first decreased, then increased. Characteristics that reflect the performance of photosynthesis, including the maximum net photosynthetic rate (Pnmax), apparent quantum yield (AQY), and the rate of dark respiration (Rd) also decreased in value as dormancy progressed. Overall, the total chlorophyll content, and the content of chlorophyll a, chlorophyll b, and carotenoids, exhibited continuous decreases as dormancy progressed. Correlation analysis showed that most photosynthetic physiology indices and the content of photosynthetic pigments were significantly negatively correlated with daylight duration; no significant correlations with other environmental factors were found. These results indicated that the summer dormancy of M. laxiflora remnant populations is an active dormancy that represents an adaptation of the plant to submersion in the summer. Increasing daylight duration may be the main factor that triggers summer dormancy in M. laxiflora.