Distribution characteristics of soil organic carbon stocks in typical plantations in loess hilly region of northwestern China

Objective Plantations are critical carbon pools and play important roles in carbon cycling of terrestrial ecosystems. On the Loess Plateau, analyzing the spatial distributions of soil organic carbon stocks in typical plantations provides basic data support for the accurate assessment of soil carbon sequestration capacity.

Method In our study, Wuqi County, which is located in the loess hilly region, was selected as the study area. Typical plantations including Pinus tabuliformis, Armeniaca sibirica and Hippophae rhamnoides were taken as the study objects, while natural grassland was taken as the control. Application of principal component analysis and redundancy analysis explored the spatial distribution characteristics of soil organic carbon stocks in the 0−200 cm soil and its influencing factors in a typical plantation in the loess hilly region.

Result (1) In typical plantations of the loess hilly region, soil organic carbon stocks at soil surface were significantly higher than those in the deeper soil. Across the 0−200 cm soil layers, the total soil organic carbon stocks could be arranged as: Armeniaca sibirica (97.145 g/cm²) > grassland (92.418 g/cm²) > Hippophae rhamnoides (68.695 g/cm²) > Pinus tabuliformis (61.130 g/cm²). The spatial variability of soil organic carbon stocks was greatest in Hippophae rhamnoides (0.219), while the spatial variability of soil organic carbon stocks was least in grasslands (0.115). (2) Soil organic carbon stocks were positively correlated with clay and silt but negatively correlated with sand. Soil total nitrogen and alkali-hydrolyzable nitrogen had significant positive effects on soil organic carbon stocks. (3) Across the 0−200 cm soil profile, the spatial variability of soil organic carbon stocks was primarily affected by topography (30.71%). In particular, elevation (19.66%) was the most important driving factors.

Conclusion In summary, soil organic carbon mainly accumulates at soil surface of typical plantations in the loess hilly region. Among various influencing factors, soil organic carbon stocks are mainly affected by soil texture, nitrogen, and phosphorus. In comparison to other plantations, Armeniaca sibirica performs better in carbon sequestration. Therefore, vegetation restoration using Armeniaca sibirica is highly recommended in loess hilly region.