<b>Global patterns and drivers of soil dissolved organic carbon concentration</b>

Dissolved organic carbon (DOC), being the most active carbon pool in soils, plays a crucial role in soil carbon cycling, plant productivity, and global climate change. Assessing the amount of soil DOC is essential for accurately understanding ecosystem functioning and services. Nevertheless, the global driving factors and distribution of soil DOC remain inadequately quantified because of the scarcity of large-scale data. Here, a comprehensive database of global 12807 soil DOC concentration from 975 target literature was constructed. Detailed geographic location, climate, and soil properties are also recorded as the predictors of soil DOC. Machine learning techniques were employed to assess the relative importance of various predictors in determining soil DOC concentration and subsequently extended predictions to a global scale. Global soil DOC concentration ranged widely from 0.04 to 7859 mg kg-1, with the average of 222.78 mg kg-1. The selected 12 variables (including soil properties, month, climate, and ecosystem) could explain 65% of the variance in soil DOC concentration. Elevation, soil clay, and soil organic carbon were the first three important predictors. The predicted soil DOC concentration increased significantly from the equator to the poles. Soil DOC stock in the topsoil layer (0-30 cm) amounts to 12.17 Pg, with huge variations observed across the different continents. Our results are instrumental for informing strategies on soil management practices, climate change mitigation, and ecosystem services. In addition, our database combines with other carbon pool to explore total soil carbon turnover and constrain Earth carbon models.