Impact of severe burning on organic carbon and black carbon in soil aggregates in natural Larix gmelinii forest of Great Xing’an Mountains

The objective of this study was to reveal the changes of organic carbon (SOC) and black carbon (BC) in soil aggregates after severe burning. With unburned natural Larix gmelinii forest as contrast, we selected severely burned area of natural L. gmelinii forest in Great Xing’an Mountains as research object. The effect of severe burning on organic carbon and black carbon in soil aggregates was studied. The results showed that: 1) After severe burning, the contents of organic carbon and black carbon of surface soil significantly increased. Compared with contrast sample plot, soil organic carbon content in 0-5 cm soil layer increased by 41.56%, and black carbon content significantly increased by 123.69% (P0.05).2) Severe burning significantly increased the percentages of aggregates smaller than 0.25 mm and larger than 5 mm (P0.05), but the percentages of 0.25-5 mm all decreased in 0-5 cm soil layer.3) Compared with contrast sample plot, severe burning significantly increased the organic carbon content of aggregates smaller than 0.053 mm and larger than 5 mm by 127.27% and 177.6% (P0.05), respectively. Organic carbon content of 0.25-2 mm aggregates in three soil layers was lower than contrast sample plot tovarying degrees.The content of soil organic carbon in aggregates increased with the increase of particle size in the two kinds of forest, and showed a trend of decreasing with the increase of soil depth. 4) The characteristics of distribution of black carbon in aggregates were similar to organic carbon. After severe burning, black carbon of aggregates 5 mm,2-5 mm,0.053-0.25 mm and 0.053 mm increased by 4.92,4.19,1.06 and 0.44 g/kg in 0-5 cm soil layer, which was significantly different with contrast sample plot (P0.05). 5) The BC/SOC ratio ranged from 0.05 to 0.41 in two kinds of forest, and severe burning significantly increased BC/SOC ratio (P0.05). A significant correlation was found between organic carbon and black carbon contents in aggregates of each size class.