biostudies-literatureZhou GChinese Academy of SciencesNational Natural Science Foundation of China746-757https://www.ebi.ac.uk/biostudies/studies/S-EPMC8291401biostudies-literatureUnknown6(4)Soil organic carbon (SOC) plays critical roles in stabilizing atmospheric CO₂ concentration, but the mechanistic controls on the amount and distribution of SOC on global scales are not well understood. In turn, this has hampered the ability to model global C budgets and to find measures to mitigate climate change. Here, based on the data from a large field survey campaign with 2600 plots across China's forest ecosystems and a global collection of published data from forested land, we find that a low litter carbon-to-nitrogen ratio (C/N) and high wetness index (P/PET, precipitation-to-potential-evapotranspiration ratio) are the two factors that promote SOC accumulation, with only minor contributions of litter quantity and soil texture. The field survey data demonstrated that highNational science reviewClimate and litter C/N ratio constrain soil organic carbon accumulation.PMC8291401XDA05050000NSFC41430529Liu JCiais PFang JZhang DDu SLu XYu GMa YWang GLiu SHan SManzoni SZhang QRen HChu GZhou GWang WChen XTang XYan JZhou PLi YLi SHuang WXu SMa KfalseClimate and litter C/N ratio constrain soil organic carbon accumulation.Soil organic carbon (SOC) plays critical roles in stabilizing atmospheric CO₂ concentration, but the mechanistic controls on the amount and distribution of SOC on global scales are not well understood. In turn, this has hampered the ability to model global C budgets and to find measures to mitigate climate change. Here, based on the data from a large field survey campaign with 2600 plots across China's forest ecosystems and a global collection of published data from forested land, we find that a low litter carbon-to-nitrogen ratio (C/N) and high wetness index (P/PET, precipitation-to-potential-evapotranspiration ratio) are the two factors that promote SOC accumulation, with only minor contributions of litter quantity and soil texture. The field survey data demonstrated that high2019-01-01T00:00:00Z2019 Jul2025-04-19T20:43:29.916Z2025-04-19T20:43:29.916ZS-EPMC82914013469193010.1093/nsr/nwz045