Abstract: Forest is the most important carbon pool of terrestrial ecosystems, of which the forest plantations become more and more crucial. We investigated the differentaged poplar plantations in Tianjin through field surveys and laboratory measurements, estimated the carbon stock in the tree layer, herb layer, litter layer and soils (0-100 cm). The results showed that the biomasses of the tree layer in the young, medium and matured poplar plantations were 43.65, 56.18 and 121.59 t·hm^-2, respectively. The proportions of different organs to the tree biomass were in the order of stem>root>branch>leaf  in the young and medium age stands, and of stem>branch>root>leaf in the matured poplar plantations. The biomasses of the herb layer of the three age plantations were 4.60, 2.92 and 1.58 t·hm^-2, respectively, and that of the litter layer were 0.46, 0.35 and 0.66 t·hm^-2, respectively. The total ecosystem carbon storage values of the young, medium and matured poplar plantations were estimated to be 84.34, 121.03 and 121.72 t C·hm^-2, respectively. Among the carbon storage of the three age groups, plant communities accounted for 25.85%, 22.25% and 46.58%, respectively, and soils accounted for 74.15%, 77.75% and 53.42%, respectively. The carbon storage values of the tree layer in the young, medium and matured poplar plantations were 20.04, 25.78 and 55.95 t C·hm^-2, respectively. The carbon storage values of the herb layer in the three age groups were 1.63, 1.05 and 0.57 t C·hm^-2, respectively, and that of the litter layer were 0.14, 0.10 and 0.19 t C·hm^-2, respectively. The soil organic carbon storage values (0-100 cm) in the three age groups were 6253, 94.10 and 65.03 t C·hm^-2, respectively. The proportions of the carbon storage in the 0-30 cm soil layer to that of the total soil layer were 33.91%, 37.64% and 44.16%, increasing with the stand age.  It was showed that the ecosystem carbon storage of the poplar plantations in Tianjin increased with the increasing stand age. Nowadays, the young poplar plantations account for a large proportion of the total forest plantations in Tianjin. Thus, the poplar plantations in Tianjin would have a huge carbon sequestration potential in the future.

Key words: nitrogen fertilizer, quality., greenhouse, cucumber, yield