Effects of sieving process on soil organic carbon mineralization for two forest types in Xiaoxing'an Mountains, Northeast China

We explored the effects of sieving process on soil organic carbon (SOC) mineralization in broad-leaved secondary forest and virgin Korean pine forest in the Xiaoxing'an Mountains by using incubation method. The SOC mineralization rate, cumulative SOC mineralization (C_m), and the content of cool water extractable carbohydrate (CWEC) and hot water extractable carbohydrate (HWEC) before and after incubation were measured; the simultaneous reaction model was employed to estimate SOC mineralization parameters including soil easily mineralizable C (C₁) and potentially mineralizable C (C₀); the correlations between C_m, CWEC and HWEC were also analyzed. Results showed that both the mineralization rate and C_m of SOC in the broadleaved secondary forest were greater than the ones in the virgin Korean pine forest. Both the mineralization rate and C_m of SOC in two forests were increased by sieving process, and C_m in the soil sieved to 1 mm was increased more than that in the soil sieved to 2 mm. The sieving process had a decreasing impact on the mineralization rate of SOC in the two forest types as the incubation time increased, while it had little impact on C₀ but did increase C₁ by 49.09%-68.06% in 2 mm sieved soil and 91.03%-133.83% in 1 mm sieved soil. The sieving process increased the CWEC, but had no effect on the HWEC. Significantly positive correlations had been observed between the C_m and both the initial and changed contents of CWEC and HWEC, indicating that water extractable carbohydrate was the key factor for the mineralization of the organic carbon in soil, and that the loss of carbohydrates could largely explain the CO₂ released during the soil organic carbon mineralization. In conclusion, the sieving process could destroy the soil structure, release some carbohydrates from soil aggregates, and increase the mineralization level of the organic carbon in soil.