Storage Potential of Soil Functional Carbon Fractions in the World's Largest Plantations

The expansion of planted forests is one of the most effective natural climate solutions. However, increasing forest age and climate change lead to weaken biomass carbon sink, highlighting the urgency of improving the storage of functional soil organic carbon (SOC) to maintain a high level of carbon sink on a long-time scale. Using data from 501 planted forests and 564 natural forests across China, it is found that climate warming and drying increase the loss of topsoil (0-20 cm) mineral-associated (MAOC) and particulate organic carbon (POC) during the conversion of natural forests to plantations. High-precision random forest models for MAOC (77%) and POC (75%) derive the storage of the functional SOC in planted and natural forests. The total deficit of SOC in plantations compared to natural forests is $2.{17}_{1.87}^{2.52}$ Pg SOC (mean with 5% and 95% quantile). This substantial potential can be gained by plantation management, such as close-to-nature management. The minimal (14.61 Pg C), intermediate (22.36 Pg C), and ambitious (29.79 Pg C) objectives of SOC storage potential, providing science-based targets for enhancing soil carbon sinks, are also estimated. Overall, these findings provide a transferable framework to assess functional SOC benchmarks and targets for policymakers and highlight the strategic role of plantation soils for global carbon neutrality goals.