Long-term effects of afforestation and thinning on greenhouse gas emissions from temperate abandoned-land soil in the Northeast of China

CO₂, CH₄ and N₂O annual emission fluxes from larch plantations (50 years old) on abandoned farmland under different thinning intensities (no thinning, contrast; mild thinning, 25% and severe thinning, 50%, tinning operation has been done for 20 years) and farmland on the corresponding site were measured by the static chamber method in temperate Maoershan Mountains in northeastern China to reveal the long-term effects of afforestation and thinning on greenhouse gas emissions from abandoned-land soil. The results showed that: 1) CO₂ emission flux (149.44-204.82 mg/(m²·h)) took on a trend of no thinning > farmland > mild thinning > severe thinning, which increased by 11.6% at no thinning site than farmland site, yet they decreased by 11.4%-18.6% at mild and severe thinning sites compared with farmland site, and both also decreased by 20.6%-27.0% significantly compared with no thinning. 2) CH₄ fluxes (-0.027-0.033 mg/(m²·h)) showed a trend of severe thinning > no thinning = farmland > mild thinning, there was no significant difference between no thinning site and farmland site, but it decreased by 12.9% at mild thinning site, and increased by 6.5% at severe thinning site than farmland site. 3) N₂O emission fluxes (0.025-0.037 mg/(m²·h)) presented a trend of farmland > severe thinning > mild thinning > no thinning, which decreased by 32.4% at no thinning site, and decreased by 24.3%-29.7% at mild and severe thinning sites than farmland site. 4) the correlation between CO₂, CH₄ and N₂O emission fluxes and the air temperature and soil temperature were not changed by afforestation and thinning, but the correlation among three kinds of greenhouse gases and soil moisture were changed. 5) The global warming potential (GWP) (13.89-18.64 t/(ha·yr)) showed the trend of no thinning > farmland > severe thinning > mild thinning, which increased by 9.1% at no thinning site, and decreased by 12.1%-18.7% at mild and severe thinning sites than farmland site, both also decreased by 19.4%-25.5% compared with no thinning site. Therefore, afforestation increased the global warming potential on the temperate abandoned land in northeastern China, thinning greatly reduced the global warming potential, so severe intensity thinning (50%) should be more suitable for larch plantation on temperate abandoned land to control the climate warming.