Whole-Soil-Profile Warming Enhances CO2 Fluxes in an Alpine Peatland on the Tibetan Plateau

Tibetan Plateau peatlands store substantial organic carbon and are highly vulnerable to climate warming, yet the response of CO2 emissions to whole-soil-profile warming remains unclear. We conducted a two-year whole-soil-profile warming experiment (0–300 cm) in a Zoige peatland with four treatments: control (CK), moderate warming (+2.5 °C, W2.5), high warming (+5 °C, W5), and variable warming (0–8 °C, VT). CO2 responses to warming were non-linear, season-dependent, and intensified over time. W5 significantly increased growing-season CO2 fluxes to 345.52 and 394.57 mg m−2 h−1 in 2022 and 2023, respectively. During the non-growing season, warming had no significant effect in the first year, whereas all warming treatments significantly increased CO2 fluxes in the second year. Principal component analysis further indicated a temporal shift in the factors associated with CO2 emissions, from carbon availability (DOC and SOC) in the first year toward inorganic nitrogen (NH4+-N and NO3−-N), available phosphorus, and soil environmental conditions (e.g., Eh) under prolonged warming. These findings highlight the importance of warming intensity, duration, and belowground biogeochemical reorganization in regulating alpine peatland carbon–climate feedbacks.