Abstract:Mikania micrantha is notorious for its strong ability to colonize in new habitats. Existing photosynthetic studies have mainly focused on leaves, and less on non-photosynthetic organs such as stems, roots, and reproductive organs. The aim of this study was to clarify the photosynthetic characteristics of each such organ and its possible contribution to total carbon sequestration of the population. By taking the leaf as control, the photosynthetic electron transportation rate (ETR), PSII photochemical efficiency (ΔF/Fm) and photosynthetic rate (P) under saturation light, chlorophyll content (Chl.a+b) and carotenoid (Car.) content of the flower, fruit, stem and green root were measured. Although the ETR and ΔF/Fm of these non-photosynthetic organs were lower than those of the leaf, the ETR/Chl.a+b and ETR/Car. were much higher, indicating that the photosynthetic pigments are more efficiently utilized in non-photosynthetic organs than in leaves. In the reproductive season, the scaling-up of photosynthetic capacity from the organ level to the community level showed that all non-photosynthetic organs took up 19% and 49% of the total carbon sequestration by the IRGA method and the chlorophyll fluorescence method, respectively. Although leaf photosynthesis of this weed is of the C3 type, a C4-like vascular bundle full of chlorophyll was observed in the main vein of the leaf and young stems. In conclusion, the high efficiency of the C4 pathway compared to the C3 pathway might be devoted the high photosynthetic chlorophyll utilization efficiency (ETR/Chl.a+b) in stems, although more direct evidence is necessary to test this hypothesis.