Divergent Responses of Deep SOC Sequestration to Large-Scale Revegetation on China’s Loess Plateau

Dryland revegetation can mitigate land degradation, increase vegetation coverage and terrestrial C sinks, and substantially decrease soil water storage. However, variation in soil organic C (SOC) sequestration with precipitation under large-scale ecological restoration is unclear, and the trade-off between SOC sequestration and water consumption under different vegetation types remain controversial, particularly in deep soils. This study investigated SOC storage (SOCS) and soil water storage (SWS) in 0-1000 cm profiles under various vegetation types (woodland, shrubland, grassland, and farmland) along a precipitation gradient from 406 mm to 606 mm on China's Loess Plateau. The four vegetation types exhibited similar trends in the spatial distribution of SOCS and SWS, significantly increasing as mean annual precipitation (MAP) increased, except for SWS in shrubland. In contrast, deep SOC sequestration and water deficit effects varied with vegetation type and MAP. Specifically, & UDelta;SOCS (SOCS difference between restored vegetation and farmland) of woodland significantly decreased with increasing MAP, whereas no significant relationship occurred for shrubland and grassland; significant positive and negative linear correlations occurred between & UDelta;SWS (SWS difference between restored vegetation and farmland) and MAP for woodland and shrubland, respectively, with no apparent relationship for grassland. Moreover, the three restored vegetation had positive correlations between & UDelta;SOCS and & UDelta;SWS in deep soils. Woodland had the highest SOC sequestration efficiency (& UDelta;SOCS/& UDelta;SWS) but also caused the most severe soil water deficit, while grassland had the lowest C and water effect. Therefore, shrublands are better for revegetation in semiarid regions, with relatively lower soil water deficit than woodland and higher SOC sequestration effect than grassland; multispecies forest plantations dominated by R. pseudoacacia may be more suitable than single species plantations in semihumid regions. These findings highlight the SOC sequestration potential of deep soils and offer insights into dryland revegetation.