关键词: 耐水湿树种, 水下光合作用, 气膜, 叶片性状, 耐淹性

Abstract: Aims To explore the characteristics of underwater photosynthesis of six water-tolerant tree species commonly planted in wetland, East China, and then reveal the effects of leaf morphological and physiological traits on the underwater net photosynthetic rate (PN), so as to provide a scientific basis for the selection of afforestation tree species in low-lying lands. Methods The morphological and physiological traits of leaves, as well as underwater PN of leaves with or without gas film of six water-tolerant tree species, including Taxodium hybrid ‘zhongshanshan406’, Metasequoia glyptostroboides Hu & W.C.Cheng, Pinus elliottii Engelm., Triadica sebifera (L.) Small, Salix babylonica L., and Bischofia polycarpa (H. Lév.) Airy Shaw were determined. The relationships between leaf traits and underwater PN were analyzed by T-test, Pearson and Point-Biserial Correlation Analysis. Important findings (1) The specific leaf area of M. glyptostroboides and the chlorophyll content of T. sebifera were significantly higher (p < 0.05) than those of other tree species, while those of P. elliottii were the lowest. The water droplet contact angles at both leaf ends of T. hybrid ‘Zhongshanshan406’ and T. sebifera were greater than 125°, showing great hydrophobic characteristics of leaves. However, those of P. elliottii and B. polycarpa were between 60° and 82°, indicating hydrophilic characteristics. In the case of M. glyptostroboides and S. babylonica, the contact angles were 130.20° and 130.23° at the distal end and 87.97° and 88.37° at the near axial end, respectively. The leaf gas film thickness of M. glyptostroboides and T. hybrid ‘Zhongshanshan406’ were the largest, 25.86 μm and 22.17 μm, respectively, while that of B. polycarpa was only 1.06 μm. (2) The CO2 uptake of all six tree species followed the FvCB photosynthetic model: photosynthesis was limited by CO2 supply at low CO₂ concentration. As the CO2 concentration increases, it gradually transitions to the light energy or enzyme activity limitation phase. The underwater PN increased rapidly with the increase of photosynthetically active radiation and then gradually stabilized. The optimal temperature of underwater photosynthesis of M. glyptostroboides was about 23°C, while those of other tree species were 25~30°C. Under the same photosynthetically active radiation, CO2 concentration and temperature, both T. hybrid ‘Zhongshanshan406’ and M. glyptostroboides showed higher underwater PN. (3) Correlation analysis showed that leaf gas film was significantly positively correlated with the underwater PN (r = 0.809, p < 0.01). It increased the underwater PN by 1.4~13 times (p < 0.05) when compared with those without leaf gas film. In addition, the specific leaf area and leaf contact angle were significantly positively correlated with underwater PN (r=0.548, p < 0.05; r=0.517, p < 0.05), while no significant correlations between chlorophyll content and stomatal density and underwater PN were found. In conclusion, underwater PN showed a typical response trend to photosynthetically active radiation, CO2 concentration and temperature. Leaf gas film thickness, specific leaf area and hydrophobicity could be used as important indicators to evaluate the underwater photosynthetic ability of water-tolerant tree species. T. hybrid ‘Zhongshanshan406’ shows the strongest photosynthetic potential under water and is a suitable tree species for the greening of low-lying lands.

Key words: water-tolerant tree species, underwater photosynthesis, gas film, leaf traits, flood resistance