Abstract: Aims Methane (CH₄) plays an important role in the greenhouse effects. Our objectives were to evaluate the CH₄ budget, understand seasonal variation of CH₄, and explore effects of temperature and moisture on CH₄ flux in a mid- subtropical pine plantation to provide data for estimating the influence of subtropical forest ecosystems on greenhouse effects. 
Methods We analyzed CH₄ flux from soils in the Qianyanzhou red earth hill region of China for 16 months from September 2004 to December 2005, using a static chamber-gas chromatograph technique.
Important findings The soil of this type of pine plantation was a sink of CH₄ to the atmosphere as a whole; annual CH₄ flux ranged from 7.67 to -67.μg•m^-2•h^-1 with average of -15.530 μg•m^-2•h^-1under a forest soil treatment and from 9.31 to -90.36μg•m^-2•h^-1 with average of -16.μg•m^-2•h^-1 under a litter-free treatment. CH₄ absorption had similarly seasonal variations with a sequence of autumn > summer > spring > winter for both treatments, but differed in variation ranges and time. The litter-free soil had larger ranges of seasonal variations, maximum CH₄ sink was in October and minimum sink was in March. Meanwhile , the corresponding maximum and minimum CH₄ sinks in the forest soil were in the September and February, respectively, a month earlier than litter-free treatment. Analysis of correlations between CH₄ flux and temperature and moisture showed that CH₄ flux had a significant positive correlation to soil temperature at 5 cm depth and a significant negative correlation to soil water content at 5 cm depth. Partial correlations showed the combined effects of moisture and temperature on CH4 flux in different seasons. Temperature was a limiting factor for soil absorption of CH₄ during winter (December to February), but soil absorption increased during the rainy season (March to May). From July to August, CH₄ absorption increased with the declining soil moisture but was restricted by high temperature. During the fall (September to November), CH₄ absorption reached the maximum value for suitable combined effects of temperature and moisture. In summary, CH₄ absorption increased with soil temperature and decreased with soil water content, but was restricted by high temperature.