Effects of ecological afforestation on soil inorganic carbon in arid region: a case study of desert margin in Alxa region, China

Alxa is a region with severe land desertification and extreme ecological fragility in China. The ecological afforestation in the area has effectively curbed the desertification of the local land. However, studies on soil inorganic carbon (SIC) dynamics after sandy land ecological afforestation are still few. Understanding SIC profiles' distribution and stock changes after ecological afforestation is essential for assessing regional, continental, and global soil carbon sink potential. We investigated the characteristics of SIC from 0 to 300 cm depth with increasing stand age using plantation forests of Haloxylon ammodendron grown for 5, 11, 22, and 46 years on the edge of the desert in Alxa region, with a nearby mobile sand (MS) with no vegetation cover as a control. Within the 0–300 cm soil layer, SIC storage increased significantly (6.52 kg m −2 ) after ecological afforestation compared to MS over 46 years. SIC sequestration rate decreased with increasing stand age, in the order of 5 years (0.054 kg m −2 yr −1 ), >11 years (0.025 kg m −2 yr −1 ), >22 years (0.016 kg m −2 yr −1 ), and >46 years (0.009 kg m −2 yr −1 ). The 100–300 cm SIC storage accounts for over 60% of the SIC pool. Soil carbon pool estimation will be largely underestimated if only the shallow SIC is considered.