3.4 Variation in SIC storage
The SIC storage in the soil layers of 0 ~ 100 cm and 100 ~ 300 cm at different stand ages are shown in Fig. 6. The SIC storage of MS, 5yrs, 11yrs, 22yrs, and 46yrs in 0 ~ 100 cm soils was 2.15 kg m-2、3.30 kg m-2、3.47 kg m-2、3.77 kg m-2, and 4.14 kg m-2, respectively. The SIC storage in the 100 ~ 300 cm soil layer was 4.89 kg m-2、7.76 kg m-2、7.68 kg m-2、8.39 kg m-2, and 9.43 kg m-2, respectively. Figure 6b indicates that there is still a large amount of SIC storage in the soil layer below 100 cm, and its proportion accounts for more than 60% of the SIC storage in the soil layer from 0 to 300 cm. This result indicates that in arid and semi-arid regions, SIC below 1 m is not negligible in soil carbon stock estimation.
As can be seen from Figure 7, CSR was greatest at 5yrs and least at 46yrs during the MS to 46yrs stand age growth stage. That is, the proportion of the net increase in inorganic carbon stock from MS to 46yrs decreases with increasing stand age. Throughout the study period, CSR in the 0-300 cm soil layer was in the following order: 5yrs (0.054 kg m-2 yr-1) > 11yrs (0.025 kg m-2 yr-1) > 22yrs (0.016 kg m-2 yr-1) > 46yrs (0.009 kg m-2yr-1). The results of this study indicate that CSR decreases continuously with increasing stand age.