Active Restoration of Carbon Poor Degraded Grassland Accelerated Subsoil Carbon Accumulation and Turnover

Grassland degradation and its impact on soil carbon cycle is of worldwide concern, but optimal restoration strategies remain uncertain. We determined temperature sensitivity of organic cabon mineralization (CO₂-Q₁₀) and the mechanisms underlying changes in soil organic carbon (SOC) content across non-restored and restored grasslands on the Qinghai-Tibetan Plateau. Topsoil and subsoil with three SOC contents from non-restored and passively or actively restored grasslands were incubated for 28 days at 5, 15, and 25°C. We determined the Q₁₀ of SOC mineralization, and the importance of vegetation, soil physico-chemical properties and microbial communities regulating CO₂-Q₁₀. In C-poor soil, SOC mineralization rate was slowest with active restoration, but SOC storage increased in both topsoil and subsoil. Increased soil pH and C availability raised CO₂-Q₁₀ in the actively restored grassland. In subsoil of C-middle soil, SOC storage in passively and actively restored grasslands were 81% and 25% greater, respectively, than in non-restored grassland. In the topsoil of C-rich soil, passively restored grassland had less SOC storage (7.5 kg·m⁻²) than non-restored grassland (10 kg·m⁻²), because the greater aboveground biomass increased SOC decomposition caused by the priming effects driven by organic inputs from litter. The CO₂-Q₁₀ in C-rich topsoil in passively restored grasslands (1.1) was less than in non-restored grassland (1.3). These findings emphasize that effective restoration management should consider initial organic C content of the degraded grassland to develop the best ecological restoration approaches to maximize C storage and limit CO₂ emission into the atmosphere.