Abstract: Floodplain wetlands have a significant capacity for carbon sequestration but are vulnerable to land use changes. Poplars are extensively planted in wetlands due to the increasing demand for wood products and bioenergy. Although the large biomass of poplar may increase the carbon stock in wetlands, a high transpiration rate may reduce soil moisture, thereby improving the aeration of wetland soils and facilitating the oxidation of organic materials. Therefore, the impact of poplars on wetland carbon stocks is undetermined and remains unexplored. Here, we investigated the effects of poplar plantations on biomass carbon stocks (BCS) and soil organic carbon (SOC) stocks in Dongting Lake wetlands, China, using native Miscanthus lutarioriparius vegetation as a control. Our results indicated that the BCS of middle-aged and near-mature poplar plantations (36.47–81.34 t ha⁻¹) was higher than that of M. lutarioriparius (8.31 t ha⁻¹), and it increased with stand age. The SOC stocks within the 0–60 cm depth in young, middle-aged, and near-mature poplar plantations (130.32–152.58 t ha⁻¹) were higher than those in M. lutarioriparius (70.48 t ha⁻¹), but it did not increase with stand age. The BCS was positively associated with soil bulk density, and the SOC stocks were negatively associated with soil sand content. Overall, our findings indicate that poplar plantations increase carbon stocks in the Dongting Lake wetlands. Nevertheless, the long-term effect of poplar plantation on carbon sequestration in floodplain wetlands should be further investigated.

Key words: carbon storage, soil organic carbon, Populus deltoides, forest stand age, Dongting Lake