Abstract: Based on an extensive collection of information and experimental data, this paper studied the carbon cycle in ten kinds of forest ecosystem in Guangzhou, China, aimed to explore the carbon cycling patterns in southern subtropical forest ecosystems. For the test ecosystems, their carbon density ranged from 108.35 to 151.85 t C·hm^-2, with 10.85-48.86 t C·hm^-2 in tree layer and 87.74-99.01 t C·hm^-2 in soil layer (0-60 cm), being lower than the national average. There were 4.41-9.15 t C·hm^-2·a^-1 flowed from atmosphere to vegetation stratum, 0.74-2.06 t C·hm^-2·a^-1 from vegetation stratum to soil, and 3.94-5.42 t C·hm^-2·a^-1 from soil to atmosphere, i.e., the forest systems absorbed 0.47-4.97 t C·hm^-2·a^-1 from atmosphere. The net ecosystem production (NEP) varied with forest stand, being higher for broadleaved forest than coniferous forest, mixed forest than pure forest, and natural secondary forest than artificial forest.

Key words: carbon density, carbon flu, carbon cycle, forest ecosystem, Guangzhou, assimilation carbon, mineralization, transformation, soil ¹⁴C labeling.