Abstract: Based on the investigation of biomass and the measurement of CO₂ and CH₄ fluxes, the CO₂ exchanges between mangrove- and shoal wetland ecosystems and atmosphere in Guangzhou were studied, and the CO₂ absorption capability of the wetlands vegetation net productivity as well as the carbon sink function of the wetlands under different waterlogged conditions (perennial, intermittent, and no water-logging) was analyzed. As for mangrove wetland ecosystem, its vegetation net productivity absorbed 33.74 t·hm^-2·a^-1 of CO₂, and soil emitted 12.26 t·hm^-2·a^-1 of CO₂ (including the greenhouse effect amount of CH₄ converted into that of CO₂), illustrating that mangrove wetland had a 21.48 t·hm^-2·a^-1 net absorption of CO₂, being a strong carbon sink. For shoal wetland ecosystem, its vegetation net productivity absorbed 8.54 t·hm^-2·a^-1 of CO₂, and soil emitted 5.88 t·hm^-2·a^-1 of CO₂ and 0.19 t·hm^-2·a^-1 of CH₄. If converting into carbon, the wetland absorbed 2.33 t C·hm^-2·a^-1, and soil emitted 1.74 t C·hm^-2·a^-1 (including the carbon in CH₄), illustrating that shoal wetland fixed 0.59 t C·hm^-2·a^-1, being a weak carbon sink. If the greenhouse effect amount of CH₄ was converted into that of CO₂, the soil emitted 9.78 t·hm^-2·a^-1 of CO₂, which was 1.24 t·hm^-2·a^-1 more than the absorption. As a result, shoal wetland was a weak carbon source. Between the two test greenhouse gases, CH₄ was the main one emitted under perennial water-logging, while CO₂ was that under no water-logging. Moreover, the wetland under perennial water-logging had the strongest carbon sink function, while that under no water-logging was in adverse.

Key words: phytoplankton, seed bank, cyst, carbon cycling, research progress