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Surface litter layer strongly influences CO₂, N₂O, and CH₄ fluxes (<i>F</i>_CO2, <i>F</i>_N2O, and <i>F</i>_CH4) between the atmosphere and forest floor through litter decomposition (litter-internal, f_L-L) or interactions between litter and mineral soil (litter-induced, f_L-S). However, the relative contribution of f_L-L or f_L-S to these greenhouse gas (GHG) fluxes in forests at different succession stages remain unclear. We conducted a field experiment where surface litter was either removed (LR), left intact (CT), doubled (LD), or exchanged (LE) in a Masson pine forest (PF, early stage of succession) and an evergreen broadleaved forest (BF, climax of succession) at the Dinghushan Nature Reserve in southern China, and studied the responses of <i>F</i>_CO2, <i>F</i>_N2O, and <i>F</i>_CH4 from August 2012 to July 2013. The results showed that both <i>F</i>_CO2 and <i>F</i>_N2O were increased by LD treatment with a greater increase in BF (41% for <i>F</i>_CO2 and 30% for <i>F</i>_N2O) and decreased by LR treatment with the greater decrease in PF (−61% for <i>F</i>_CO2 and −58% for <i>F</i>_N2O). LD treatment decreased <i>F</i>_CH4 by 14% in PF and 6% in BF, and LR treatment increased <i>F</i>_CH4 by 5% in PF and 18% in BF. f_L-S contributed more to <i>F</i>_CO2 (36%) and <i>F</i>_N2O (45%) than f_L-L in PF, whereas contributions of f_L-L to <i>F</i>_CO2 (41%) and <i>F</i>_N2O (30%) were much bigger than f_L-S in BF. The greater <i>F</i>_CH4 in PF and BF resulted from the contributions of f_L-L (−14%) and f_L-S (−12%), respectively. Our results indicated that f_L-L is the major source of GHG fluxes in BF, whereas f_L-S dominates GHG fluxes in PF. The results provide a scientific reference for quantifying the contributions of f_L-L and f_L-S to GHG fluxes during the subtropical forest succession and should be considered in ecosystem models to predict global warming in the future.