Abstract: Understanding the effects of thinning intensity and fertilizer application on soil greenhouse gas emissions of forest plantations is important to accurate assessment of the capacity of greenhouse gas emissions from plantation soils. In this study, three levels of thinning intensity (mild, moderate, and severe) and two levels of fertilizer application (no fertilization and fertilization) were carried out in a subtropical Chinese fir (Cunninghamia lanceolata) plantation in China to investigate the effects of thinning intensity and fertilization  on soil CO₂, CH₄ and N₂O emissions and global warming potentials (GWPs). Soil physicochemical properties were measured to clarify the main factors that regulating soil greenhouse gas emissions. The results showed that mild thinning intensity significantly increased soil CO₂ emissions and CH₄ absorption compared with moderate thinning intensity. Fertilization together with mild thinning intensity significantly increased soil temperature sensitivity (Q₁₀). Fertilization combined with moderate thinning intensity significantly decreased soil N₂O emission, while fertilization combined with severe thinning intensity significantly increased soil CO₂ and N₂O emissions and CH₄ absorption. From the perspective of GWPs, the combined treatment of severe thinning intensity and fertilization had the largest GWPs, followed by mild and moderate thinning intensity. Throughout the observation period, Chinese fir plantation soil was CO₂ and N₂O source, but CH₄ sink. Soil moisture was the dominant factor regulating soil CO₂ emission and CH₄ absorption, followed by soil available N. Soil N₂O emissions were controlled by soil temperature. The results indicated that different thinning intensities and fertilization treatments had significant effects on soil greenhouse gas emissions and GWPs of Chinese fir plantations by changing soil moisture, temperature and N availability. Moderate thinning had better potential in reducing soil greenhouse gas emissions.

Key words: thinning intensity, fertilization, Chinese fir plantation, GHG-S emission, GWP-S.