Background <p>Plant litter input plays an important role in controlling soil organic carbon (SOC) turnover and the flow of carbon (C) among different pools. However, the relative effects of aboveground and belowground root litter on soil aggregate C dynamics across different forest types and along climate gradients remain poorly understood. In this study, we examined changes in soil aggregate mass proportion, litter-derived and native C contents of macro-aggregate, micro-aggregate and silt + clay fractions, and C flow among these fractions during 2&#xa0;years of litter input, using ¹³C isotope tracing technique in tropical, temperate and boreal forests along a climate gradient in China.</p> Results <p>The results showed that belowground root litter input enhanced soil aggregation across all three forests, but aboveground litter input had no significant effect. Belowground root litter input increased total and litter-derived C content across aggregate fractions compared to aboveground litter input in the tropical forest, while it decreased native C content in the same forest. However, the effects of litter input on total and litter-derived C contents were minimal in the boreal and temperate forests. In addition, patterns of soil C flow among aggregates varied depending on both litter input type and forest type.</p> Conclusions <p>Our results imply that belowground root litter enhances soil aggregation and aggregate C turnover compared to aboveground litter input. Moreover, the effects of root litter input on soil aggregate C turnover and C flow depend on forest types along the climatic gradient.</p>