Abstract: 【Objective】In order to provide a reference for cultivar selection of saline land, leaf photosynthetic responses to salt stress in diploid and tetraploid honeysuckle, especially the effects of salt stress on PSⅠand PSⅡperformance and coordination were studied, the difference in leaf photosynthetic characters under salt stress was compared and the effects of salt stress on leaf Na⁺, Cl^- and malondialdehyde contents and the leaf biomass were analyzed so that revealed salt tolerance of the honeysuckle with different ploidies.【Method】Tetraploid and diploid honeysuckle plants were used as experimental materials to study the effects of moderate (150 mmol·L^-1 NaCl) and severe (300 mmol·L^-1 NaCl) salt stress on photosynthesis and photosynthetic apparatus by simultaneously analyzing chlorophyll a fluorescence transient and light reflection at 820 nm as well as gas exchange parameters. Honeysuckle plants were planted in plastic pots filled with quartz sand and cultured with Hoagland nutrient solution. NaCl was added to nutrient solution incrementally by 50 mmol·L^-1 step per day to provide final concentrations of 150 and 300 mmol·L^-1 for salt treatment, and the treatment lasted for 15 days. The control plants were cultured with nutrient solution without adding NaCl. During salt treatment, expanded leaves from the middle of a shoot were sampled for measuring parameters.【Result】Under moderate salt stress, leaf photosynthetic rate, stomatal conductance and intercellular CO₂ concentration were significantly decreased in diploid and tetraploid honeysuckle, and the decrease was lower in the tetraploid, indicating less stomatal inhibition on photosynthesis. Under severe salt stress, leaf photosynthetic rate was also significantly decreased in diploid and tetraploid honeysuckle, and the tetraploid could maintain higher photosynthetic activity than the diploid due to the lower decrease in leaf photosynthetic rate. After 7 days of severe salt stress, leaf carboxylation rate and Rubisco activation state were significantly decreased in diploid honeysuckle. PSⅡphotoinhibition was induced, resulting in the decline of quantum yield of electron transport to PSⅠ. Therefore, PSⅠreduction was inhibited, and the increased PSⅠoxidation should be observed in the 820 nm reflection transient. On the contrary, PSⅠoxidation was significantly decreased. Under severe salt stress, PSⅠphotoinhibition also occurred in the leaves of diploid honeysuckle, which could not effectively drive electrons to its acceptor side and then inhibited PSⅠoxidation. The significant decrease of PSⅠoxidation resulted from the greater photoinhibition in PSⅠthan PSⅡ, and the coordination between PSⅡand PSⅠwas destroyed. After 15 days of severe salt stress, leaf carboxylation rate and activation state of Rubisco enzyme were significantly decreased in tetraploid honeysuckle, and the decrease was lower than that in diploid honeysuckle. The capacity of PSⅡand PSⅠwas not significantly affected, and their coordination was maintained in tetraploid honeysuckle under severe salt stress. Thus, tetraploid honeysuckle also had higher leaf photosynthetic activity than the diploid upon severe salt stress. After salt stress for 15 days, leaf Na⁺, Cl^- and malondialdehyde contents were significantly increased in diploid honeysuckle, whereas leaf dry weight per plant was significantly reduced, and the change amplitude was greater than that in tetraploid honeysuckle, indicating lower leaf ionic toxicity in the tetraploid, which might be responsible for maintaining higher photosynthetic capacity under salt stress.【Conclusion】Under salt stress, tetraploid honeysuckle possesses higher leaf photosynthetic activity in terms of greater leaf stomatal conductance, higher Rubisco activation state and normal PSⅡ and PSⅠcoordination, and then could accumulate greater biomass. Therefore, tetraploid honeysuckle has stronger salt tolerance and is more suitable for cultivation in saline land.

Key words: honeysuckle, photosystem, photosynthetic electron transport, stomatal limitation, carboxylation efficiency