Organic fertilization promotes the accumulation of soil particulate organic carbon in a 9-year plantation experiment

Management practices are expected to influence the capacity of forests to mitigate climate change. However, the long-term effects of afforestation on soil carbon accumulation in response to contrasting management regimes remain poorly understood. Here, we combined organic matter fractionation with a nine-year-long organic fertilization experiment to investigate the influences of largely accepted practices such as biochar (BC) and biogas-slurry (BS) inputs on the accumulation of soil particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) in three soil horizon depths (0-25, 25-50, and 50-75 cm, respectively). Our results suggested that both BS and BC significantly enhanced the POC and total soil organic carbon (SOC) content but overall did not significantly influence MAOC. Moreover, the POC and MAOC was more responsive to BS than BC. Further, our analyses revealed that the effects of BC on POC and MAOC were indirectly regulated by changes in the SOC: total nitrogen (TN) ratio, while BS influenced POC and MAOC by regulating TN. However, the responses of MAOC to the infiltration of organic fertilizers into the mineral soil should not be ignored, especially under high BC levels. Our work revealed that management practices are critical for supporting the long-term capacity of new forests to accumulate soil carbon, thereby facilitating the provision of nature-based solutions in response to climate change.