Study on Carbon Fixation and Oxygen Release Capacity of Six Typical Tree Species for Low-lying Land Greening in Eastern China

From June to August, the daily changes in net photosynthetic rate, leaf area index and crown width of six typical greening tree species in low-lying land in eastern China were measured. Their daily carbon sequestration and oxygen release capacity were then analyzed. The results show that in summer, the diurnal changes in net photo-synthetic rates of the six tree species were mainly unimodal and bimodal, and all exhibited the phenomenon of 'photosynthetic midday rest' in June and July. The leaf area index of Taxodium hybrid 'Zhongshanshan 302' was 3.12, which was significantly higher than that of other tree species (P < 0.05). The crown widths of Bischofia polycarpa and Triadica sebifera were significantly higher (P < 0.05) than those of other tree species. Additionally, the average daily carbon sequestration and oxygen release per unit leaf area of Pinus elliottii. were 4.81 and 3.50 g·m^-2·d^-1, respectively, which were significantly higher than those of B. polycarpa and Metasequoia glyptostroboides (P < 0.05). In the case of the average daily carbon sequestration and oxygen release per unit land area, they were significantly greater in T. hybrid 'Zhongshanshan 302' than those in other species, with values of 11.55 and 8.40 g·m^-2·d^-1, respectively (P < 0.05). However, M. glyptostroboides had the lowest values of 2.58 and 1.88 g·d^-1, respectively. T. sebifera had the highest whole plant carbon fixation and oxygen release with values of 665.89 and 484.28 g·d^-1, respectively, while B. polycarpa (Salix babylonica) and T. hybrid 'Zhongshanshan 302' in the middle and M. glyptostroboides being the lowest. Therefore, among all tested tree species, T. hybrid 'Zhongshanshan 302' and T. sebifera had greater capacity of carbon fixation and oxygen release. They could be used for ecological protection and carbon sequestration in low-lying land in eastern China, enhancing the comprehensive service function of the ecosystem.