Soil organic carbon fractions and sequestration across a 150-yr secondary forest chronosequence on the Loess Plateau, China

Abstract

Restoration of natural vegetation is recommended as an effective approach to restore soil function and rebuild degraded ecosystems. Information is lacking about the long-term results of secondary forest succession on the Loess Plateau with respect to soil organic carbon (SOC) fractions and sequestration in the root-zone soil profile. We investigated the differences in SOC fractions down to 100cm depths along a 150-yr chronosequence, including cropland (control) and five successional stages (pioneer weeds, herbage, shrub, early forest, and climax forest). Total, labile, and non-labile SOC concentrations increased rapidly at early successional stages (before shrub, <50-yr) and then gradually leveled off. Total SOC stock was highest at the climax forest stage (64.3Mgha−1) and lowest in cropland (39.9Mgha−1). Nearly half (~44.8%) of total SOC stock was stored in surface soils (0–20cm) and the majority (76.4%) existed in the non-labile fraction. The ratio of labile to non-labile fraction decreased with depth but remained stable across successional stages. The mean SOC sequestration potential and rate relative to cropland were 20.5Mgha−1 and 0.73Mgha−1yr−1, respectively. Although the SOC sequestration potential decreased with depth (64.7% for 0–20cm vs. 35.3% for 20–100cm), it decreased by 3.1Mgha−1 in the surface and increased by 3.4Mgha−1 in the subsurface from herbage to climax forest stage. This study indicated that long-term secondary forest succession played a positive role in SOC sequestration on the Loess Plateau, especially in the subsurface soil layers.