Poplar residue-derived biochars were larger in surface area and total pore volume but lower in nutrients and pH values than the rice straw-derived biochar. Increasing pyrolysis temperature led to a decrease in the total nitrogen content (TN) of poplar leaf- and rice straw-derived biochars, but enhanced the TN in the poplar twig- and poplar bark-derived biochars. After 180-day incubation, the total cumulative CO₂ emission decreased by 33.1–73.8% in the biochar amendments compared to their corresponding biomass residue addition, whereas the biochars derived from poplar twig and bark residues had more positive effects on reducing soil CO₂ emissions, but depended on the pyrolysis temperature.

Here, a laboratory incubation study was conducted to assess the effects of different biochars and their corresponding biomass residues on soil CO₂ emissions during the 180 days of incubation. 

Three types of poplar residues were sampled from a Nanlin-895 (Populus × euramericana cv. ‘Nanlin-895’) plantation established in March 2007, named as twig residue (the largest diameter of twigs < 3 cm, TR), bark residue (BR) and leaf residue (LR), respectively. Meanwhile, the residue of rice straw (SR) was collected from the farmland near the poplar plantation.

Biochars were prepared from the residue powders of poplar twig, bark, and leaf and rice straw using slow pyrolysis method (heating rate 10 ℃·min^-1) at 300, 500 and 700 ℃ and residence time of 4 h in a condition of hypoxia. These biochars are named in this study as follows: T1 (biochar pyrolyzed at 300℃), T2 (biochar pyrolyzed at 500℃) and T3 (biochar pyrolyzed at 700℃) for poplar twig residue, respectively. Similarly, the biochars prepared for other residues are named as B1, B2, and B3 for poplar bark residue, L1, L2, and L3 for poplar leaf residue, as well as S1, S2, and S3 for rice straw residue, respectively.