Objective  Beneficial effects of landscape plants in Suzhou on carbon-fixation, oxygen-release, atmosphere-cool, and humidity-increase during summer season were studied.

  Method  Physiologically, the photosynthetic indicators of 13 varieties of plants at Bailu Garden in in Suzhou were monitored during the summer to determine their effects on the surrounding atmospheric carbon, oxygen, temperature, and humidity.

  Result   (1) The diurnal variation on the net photosynthetic rate of the plants was mainly unimodal and bimodal, while that of the transpiration rate basically unimodal. (2) The greatest per leaf area daily carbon-fixation of 12.08 g·m⁻²·d⁻¹ and oxygen-release of 8.78 g·m⁻²·d⁻¹ were found on Ulmus parvifolia, while the lowest 3.50 g·m⁻²·d⁻¹ and 2.54 g·m⁻²·d⁻¹, respectively, on Acer palmatum Atropurpureum. The highest per leaf area daily cooling and humidifying effects of 0.38 ℃ and 2 376.15 g·m⁻²·d⁻¹, respectively, were rendered by Hibiscus syriacus, whereas the lowest 0.14 ℃ and 848.01 g·m⁻²·d⁻¹, respectively, by A. palmatum Atropurpureum. And (3) the carbon sequestration and humidification of the plants correlated positively with the net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), atmospheric humidity (RH), and photosynthetically active radiation (PAR) but negatively with the leaf water vapor pressure deficit (V_pdl).

  Conclusion   Through increasing carbon sink and mitigating hot-island effect in the surroundings with plants such as U. parvifolia, Celtis sinensis, Cinnamomum camphora, Salix babylonica, Liquidambar formosana, and Bischofia polycarpa, urban Suzhou could be environmentally improved. On the other hand, Osmanthus fragrans, Viburnum odoratissimum, and H. syriacus did not seem to offer significant benefits in that regard.