Biomass production and carbon stocks in poplar-crop intercropping systems: a case study in northwestern Jiangsu, China

The importance of agroforestry systems in CO2 mitigation has become recognized worldwide in recent years. However, little is known about carbon (C) sequestered in poplar intercropping systems. The main objective of this study is to compare the effects of three poplar intercropping designs (configuration A: 250 trees ha−1; configuration B: 167 trees ha−1 and configuration C: 94 trees ha−1) and two intercropping systems (wheat–corn cropping system and wheat–soybean cropping system) on biomass production and C stocks in poplar intercropping systems. The experiment was conducted at Suqian Ecological Demonstration Garden of fast-growing poplar plantations in northwestern Jiangsu. A significant difference in C concentration was observed among the poplar biomass components investigated (P ≤ 0.05), with the highest value in stemwood and the lowest in fine roots, ranging from 459.9 to 526.7 g kg−1. There was also a significant difference in C concentration among the different crop components (P ≤ 0.05), and the highest concentration was observed in the corn ear. Over the 5-year period, the total poplar biomass increased with increasing tree density, ranging from 8.77 to 15.12 t ha−1, while annual biomass production among the crops ranged from 4.69 to 16.58 t ha−1 in the three configurations. Overall, total C stock in the poplar intercropping system was affected by configurations and cropping systems, and configuration A obtained the largest total C stock, reaching 16.7 t C ha−1 for the wheat–soybean cropping system and 18.9 t C ha−1 for the wheat–corn cropping system. Results from this case study suggest that configuration A was a relative optimum poplar intercropping system both for economic benefits and for C sequestration.