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Methane (CH4) is the second biggest contributor to greenhouse gases, and it was found surprisingly by recent researches that terrestrial plants under aerobic conditions can also emit CH4, while currently it is still controversial on whether plants can emit CH4 under aerobic conditions or not. In recent years, most researches were based on short-term experiment in simulated and stressed environment on CH4 emittion from plants. It is inconclusive on the mechanism and source of the emission. This paper studied if CH4 emission of 51 subtropical plants at room temperature under aerobic conditions, among which Castanopsis carlesii, Castanopsis fabri, Schima superb, Cinnamomum chekiangense, Citrus, Pinus massoniana, Cunninghamia Lanceolata were selected as typical mid-subtropical plants, whose detached leaves, whole plant, branch, pectin and material abundant with pectin are the object of the study. Through indoor and outdoor cultivation of them in simulated stressed environment, possible mechanism by which plants emit CH4 is analyzed further, and possible source of the emission explored preliminarily. The results show that at room temperature under aerobic conditions,21 detached leaves of them emit CH4, with emission rate ranging from 0.11～1.37 ngCH4·g-1DW·h-1, meanwhile it is believed that plants emitting CH4 are closely related with observing conditions. Factors such as temperature, UV radiation, light, mechanical hurt and so on, have different impacts upon the emission, among which temperature apparently exerts only a short-term influence, this being one of non-enzymatic mechanisms without basically any effect upon dried leaves emitting CH4, demonstrating that pectin is not dependent on temperature. UV radiation does not strongly stimulate plants to emit CH4, and it might be studied further by removing ROS. Light enhances the emission, and this effect is significantly bigger than that exerted by higher temperature or more powerful UV radiation. However, after treatment of mechanical hurt, emission rate tends to decline, nevertheless, different degrees of mechanical hurt does not impact upon the emission. All in all, preliminary results display that the emission of CH4 may come with a higher possibility from release of CH4 dissolved in water after transpiration of plant leaves.
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