We investigated soil CH4 fluxes from six forests along an urban-to-rural gradient in Guangzhou City metropolitan area, South China. The most significant CH4 consumption was found in the rural site, followed by suburban, and then urban forest sites. The rates of CH4 uptake were significantly higher (by 38% and 44%, respectively for mixed forest and broadleaf forest) in the rural than in the urban forest site. The results indicate that soil water filled pore space (WFPS) is the primary factor for controlling CH4 consumption in subtropical forests. The reductions of soil CH4 uptake in urban forests were also influenced by the higher rates of atmospheric nitrogen (N) deposition and increases in soil nitrate (NO3−) and aluminum (Al3+) contents as a result of urbanization. Results from this work suggest that environmental changes associated with urbanization could decrease soil CH4 consumption in subtropical forests and potentially contribute to increase of atmospheric CH4 concentration.
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