Soil Organic Carbon Sequestration and Active Carbon Component Changes Following Different Vegetation Restoration Ages on Severely Eroded Red Soils in Subtropical China

Degraded soil has a high carbon sink potential. However, the carbon sequestration capacity and efficiency of comprehensive control measures in soil erosion areas are still not fully understood, and this information is essential for evaluating the effects of adopted restoration measures. The objective of this study was to determine the restoration of soil organic carbon and active carbon components under the impact of soil erosion measures and reforestation following different restoration ages. A small watershed with four typical restored plots following the same control measures (combination measures with horizontal bamboo burl-groove + replanting trees, shrubs and grasses) but different restoration ages (4 years, 14 years, 24 years and 34 years) and two reference plots (bare land (carbon-depleted) and nearby undisturbed forest (carbon-enriched)) in subtropical China was studied. The results showed that the soil organic carbon contents at a 1 m soil depth and the dissolved organic carbon and microbial biomass carbon concentrations in the upper 60 cm of soils of the four restored lands were higher than those in the bare land. Furthermore, the restored lands of 4 years, 14 years, 24 years and 34 years had soil organic carbon stocks in the 1 m soil depth of 22.83 t hm−2, 21.87 t hm−2, 32.77 t hm−2 and 39.65 t hm−2, respectively, which were higher than the bare land value of 19.86 t hm−2 but lower than the undisturbed forestland value of 75.90 t hm−2. The restored forestlands of 34 years of ecological restoration also had a high potential of being a soil organic carbon sink. Compared to the bare land, the restored lands of 4 years, 14 years, 24 years and 34 years had soil organic carbon sequestration capacities of 2.97 t hm−2, 2.01 t hm−2, 12.91 t hm−2 and 19.79 t hm−2, respectively, and had soil organic carbon sequestration rates of 0.74 t hm−2 a−1, 0.14 t hm−2 a−1, 0.54 t hm−2 a−1 and 0.58 t hm−2 a−1, respectively. Our results indicated that the combined measures of horizontal bamboo burl-groove and revegetation could greatly increase carbon sequestration and accumulation. Suitable microtopography modification and continuous organic carbon sources from vegetation are two main factors influencing soil organic carbon recovery. Combination measures, which can provide suitable topography and a continuous soil organic carbon supply, could be considered in treating degraded soils caused by water erosion in red soil areas.