Afforestation does not increase the temperature sensitivity of soil organic carbon decomposition in the water-level fluctuation zone.

Taxodium "Zhongshanshan", a flood-tolerant tree species, was primarily applied for afforestation restoration practice of soil erosion control in the water-level fluctuation (WLF) zone. However, how afforestation effects influence the temperature sensitivity (Q10) of soil organic carbon (SOC) mineralization remains poorly understood in the WLF zone under climate warming. Here, we collected soils from paired planted and unplanted plots in the WLF zone and non-flooding zone in the Three Gorges Reservoir after six years of Taxodium "Zhongshanshan" plantation. The Q10 was estimated during a 60-day incubation at 20 °C and 30 °C. Soil carbon/nitrogen fractions, potential of minerals to adsorb SOC, and SOC molecular structure were analysed at the end of the incubation. The afforestation increased cumulative SOC mineralization by 53.2% in the non-flooding zone but reduced it by 13.7% in the WLF zone over the 60-day incubation. The afforestation increased Q10 by 31.3% in the non-flooding zone but did not change Q10 in the WLF zone. The six-year plantation elevated nitrate nitrogen and dissolved total nitrogen in the WLF zone, yet reduced them in the non-flooding zone. The afforestation decreased the SOC stability in the WLF zone in contrast to the non-flooding zone. Correspondingly, the increase in the potential of minerals to adsorb SOC, indicated by the molar ratios of metals to SOC, i.e., molar (Fed + Ald)/SOC, molar (Feo + Alo)/SOC, and exchangeable Ca-to-SOC (Caexe/SOC), was greater in the WLF zone than in the non-flooding zone. Collectively, afforestation-induced shifts in SOC stability, nutrient supply, and mineral protection jointly mitigate the Q10 of SOC mineralization in the WLF zone, laying a critical theoretical foundation for wetland carbon sequestration restoration via flood-tolerant tree species.