Long-term afforestation accelerated soil organic carbon accumulation but decreased its mineralization loss and temperature sensitivity in the bulk soils and aggregates

The conversion of land use from agricultural land to forests is considered an effective measure of mitigating atmospheric CO2, but the impacts of long-term afforestation on soil organic carbon mineralization (C-m) and its temperature sensitivity (Q(10)) remain uncertain. In this study, we aimed to investigate the effects of different afforestation ages on OC contents and C-m and Q(10) in bulk soils and aggregates. Soils were collected from 0-10 cm and 10-20 cm depths in afforested woodlands after 10, 20, 30 and 40 yrs of establishment of Robinia pseudoacacia on abandoned farmlands on the Loess Plateau, China. C-m and Q(10) were measured in an 83-day incubation experiment at 25 degrees C and 15 degrees C. The results showed that long-term afforestation accelerated soil OC accumulation but decreased its C-m and Q(10) in bulk soils and aggregates, and the effects were greater at the 0-10 cm soil depth. Macroaggregates contributed most of the OC content (62%), but microaggregates and silt + clay contributed most of the OC mineralized (40% and 36%) in the bulk soils. The increased OC content and decreased C-m in aggregates suggested an increase in the sequestration of OC in fine soil particles. The temperature sensitivity of OC mineralization increased with increasing particle size, with a higher Q(10) value for macroaggregates (1.81 +/- 0.44) than for microaggregates (1.42 +/- 0.35) and silt + clay (1.31 +/- 0.14). Our results indicated that long-term afforestation would be conducive to the accumulation of OC and would decrease the release of CO2 from soils under future climate warming scenarios. The findings highlighted the OC dynamics in abandoned farmland were more sensitive to the temperature changes than those in forests, and the stability of OC in aggregates increased as the aggregate size decreased. This study contributed to bridging current knowledge gapes about the process underlying the observed OC budget and its response to warming scenarios in rehabilitated ecosystems.