Assessing Soil Carbon Components and¹⁴C to Optimize Land Use for Carbon Sequestration in the Chinese Loess Plateau

The Chinese Loess Plateau has approached a critical threshold in vegetation restoration, requiring optimized land-use strategies for sustainable ecosystem management. This study examines soil organic carbon (SOC) content and associated soil properties across 0 to 500 cm soil profiles under 4 land-use types (grassland, shrubland, forestland, and cropland) in the Gutun Basin. SOC dynamics were assessed using acid-soluble carbon (F1) and carbon components extracted at combustion temperatures of 25 to 400 °C (F2), 400 to 600 °C (F3), and 600 to 900 °C (F4). Based on¹⁴C ages, F1 to F3 were classified as labile components, whereas F4 was considered nonlabile. Although cropland exhibited the highest SOC stock (0.88 ± 0.38 kg m⁻²), it also had the highest proportion of nonlabile carbon (75%). The similar¹⁴C ages of deep-soil carbon components in shrubland and forestland, along with higher carbon content in deep layers, suggested that carbon sequestration could occur at depths of at least 300 to 500 cm. However, soil water content (SWC) in shrubland and forestland was significantly lower (93.71 ± 44.94 and 71.15 ± 17.62 g kg⁻¹, respectively), and forestland exhibited lower SOC content (1.77 ± 0.56 g kg⁻¹). Among all land-use types, grassland had a significantly higher SOC content (3.96 ± 2.56 g kg⁻¹), a greater proportion of labile carbon (77%), and a higher SWC (132.06 ± 21.71 g kg⁻¹), suggesting that it was the most suitable land-use type in this context.