Effects Of Burning On Organic Carbon And Black Carbon In Soil Aggregates Of Natural Larix Gmelinii Forests In Great Xing’ An Mountains

The objective of this study was to reveal the changes of soil organic carbon (SOC) and black carbon (BC) in soil aggregates after the fire (high-intensity fire、moderate-intensity fire、low-intensity fire). With unburned natural Larix gmelinii forest as contrast, we selected different intensity burned area of natural L. gmelinii forest in Great Xing’an Mountains as research object. The effect of different intensity burning on organic carbon and black carbon in soil aggregates was studied. The results showed that:(1) Soil organic carbon and black carbon mainly distribution in the surface soil layer. The contents of total soil organic carbon and black carbon in 0-5 cm significantly higher than 5-10 and 10-20 cm soil layer (P＜0.05). After severe burning, the contents of organic carbon and black carbon of surface soil significantly increased. Compared with contrast sample plot, soil organic carbon contents in 0-5 cm soil layer of high-intensity fire plot increased by 41.56%, and black carbon contents significantly increased by 156.44% (P< 0.05); Soil organic carbon contents in 0-5 cm soil layer of moderate-intensity fire plot decreased by 6.63% and black carbon contents significantly increased by 46.85% (P< 0.05); Soil organic carbon and black carbon contents in 0-5 cm soil layer of low-intensity fire plot had no obviously change. Show that severe burning has a significant influence on soil organic carbon and black carbon, especially in 0-5 cm soil layer.(2) Dry aggregates and water-stable aggregates over 2 mm were predominant in natural L. gmelinii forests of Great Xing’an Mountains. The particle size composition distribution of aggregates tended to be difference after different intensity fire. Particle-size (>0.25 mm) composition (PA0.25) of dry and water-stable aggregates tended to decrease after different intensity fire, but the damage rate of aggregates (PAD0.25) and fractal dimension (D) tended to increase. Mean weight soil specific area (MWSSA) of water-stable aggregates was 155.60-169.27 cm2/g, and four times bigger than dry-sieve method. MWSSA of water-stable aggregates was decreased with the increase of intensity fire, which was opposite to MWSSA of dry aggregates. Show that different intensity fire reduces the water stability and mechanical stability, especially high-intensity fire and moderate-intensity fire.(3) The contents of soil organic carbon in dry aggregates increased with the increase of particle size in the four kinds of forests, and showed a trend of decreasing with the increase of soil depth. Compared with contrast sample plot, severe burning significantly increased the organic carbon contents of aggregates smaller than 0.053 mm and larger than 5 mm in 0～5 cm soil layer by 127.27% and 177.76%(P< 0.05), respectively, organic carbon contents of 0.25～2 mm aggregates in three soil layers was lower than contrast sample plot to varying degrees. The changes of soil organic carbon in dry aggregates of both moderate-intensity fire plot and low-intensity fire plot were similar to high-intensity fire plot. In 0-5 cm soil layer, severe burning increased the contents of organic carbon in water-stable aggregates, but the contents of organic carbon in water-stable aggregates of both moderate-intensity fire plot and low-intensity fire plot had no obvious difference.(4) The characteristics of distribution of black carbon in dry aggregates was similar to organic carbon. After severe burning, black carbon of dry aggregates>5> 2～5、0.053～0.25 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 (P< 0.05). The changes of black carbon in dry aggregates of moderate-intensity fire plot and low-intensity fire plot were similar to high-intensity fire plot. Black carbon contents of water-stable aggregates all significantly increased in three soil layers after severe burning (P< 0.05). The changes of black carbon in water-stable aggregates of moderate-intensity fire and low-intensity fire plots were small.(5) The BC/SOC ratio of dry and water-stable aggregates ranged from 0.05 to 0.45 in four kinds of forests, and different intensity fire significantly increased BC/SOC ratio.(6) A significant correlation was found between organic carbon and blaek carbon contents in dry aggregates of each size class, so was total organic carbon and black carbon. But the correlation between organic carbon and black carbon contents in water-stable aggregates was lower.