Mixed plantations have more soil carbon sequestration benefits than pure plantations in China

Mixed plantation and pure plantation are two afforestation modes in practice, which make great contributions to carbon sinks of forests ecosystem. However, the difference in SOC response to the two kinds of afforestation modes (mixed plantation and pure plantation) remained controversial at present. This study conducted a synthesis to estimate afforestation modes effect on SOC sequestrations based on 218 filed observations in China. The results showed that mixed plantations preserved more SOC sequestrations than pure plantations in China. The SOC sequestration rates (RS) in 0–20 cm layer of mixed and pure plantations were 0.89 and 0.32 Mg ha−1 yr−1, respectively. Particularly, the RS of arbor-shrub mixtures (0.97 Mg ha−1 yr−1) was the highest among all mixed plantations. Generally, the RS was increased first and then decreased since afforestation, with the peaking value of 1.20 Mg ha−1 yr−1 during 6–10 years. Moreover, afforestations on cropland had a higher RS compared to that on barren lands or woodlands, and reforestations on woodlands usually led to SOC loss. Compared with high-temperature and high-precipitation environments (C-rich regions), afforestation in low-temperature and low-precipitation environments (C-deficit regions) had the higher RS. Overall, conducting mixed plantations, especially arbor-shrub mixtures, was more beneficial to promote SOC sequestration than pure plantations. The findings suggest that mixed plantations should be taken into accounting in future afforestation projects in the view of improving the carbon benefits of the ecosystem.