Combined effects of biochar addition with varied particle size and temperature on the decomposition of soil organic carbon in a temperate forest, China

The particle size of biochar is a vital parameter adjusting the soil CO2 production, whereas the effect of biochar addition with different particle sizeon soil CO2 production is still largely unclear. Furthermore, combined effects of biochar addition and temperature on CO2 production are still unknown. To address this gap, a series of incubation experiments were conducted to examine the single and interactive effects of biochar addition with three particle sizes (1-0.5 mm, 0.5-0.1 mm, and <0.1 mm) and temperature on CO2 production in a temperate forest, China. The soil samples were collected from a poplar (Populus nigra) forest in the sandy area of the ancient Yellow River in western Shandong Province, China. Cumulative CO2 production of fine-grained biochar addition (<0.1 mm) was 88.13-92.67% of that of coarse-grained biochar (1-0.5 mm). The addition of fine-grained biochar decreased CO2 production by reducing soil nitrogen availability (i.e., nitrate and ammonium) and increasing soil pH compared to the coarse-grained biochar. Biochar addition promoted the temperature sensitivity (Q(10)) of CO2 production by increasing the relative abundance of recalcitrant carbon fractions. Interactive effects of biochar addition and increasing temperature was synergistic due to the raising Q(10) value of CO2 production. Our results highlight the importance of particle size of biochar on CO2 production, less particle size of biochar, the less CO2 production. We suggest that the simultaneous effect of biochar addition and temperature on CO2 production may be underestimated basing on their single effects. Our results suggest that <0.1 mm is a threshold value of biochar particle size that is helpful to soil carbon sequestration.

Automated summary

The particle size of biochar significantly affects soil CO2 production, with fine-grained biochar reducing CO2 production compared to coarse-grained biochar. Biochar addition also increases the temperature sensitivity of CO2 production. The interactive effects of biochar addition and temperature lead to synergistic increases in CO2 production.