Abstract:

Whether plants directly release methane has remained a question. Fourteen tree species were chosen for a study of methane emission from their leaves to demonstrate whether living plants directly released methane, using a modified portable photosynthetic apparatus to collecting methane emitted from leaves and then determining the concentration of methane via gas chromatography. Furthermore, the differences in leaf methane emissions measured by in situ and in vitro methods and the effects of environmental factors (e.g., altitude) on leaf methane emissions were also explored. The results showed that methane emissions from tree leaves varied by plant species. Among the 14 tree species, methane emission was observed in Saraca dives, Artocarpus heterophyllus, and Radermachera hainanensis, and methane absorption was observed in Ficus benjamina. Both methane emission and absorption were found in the other tree species, based on the differences in concentration of methane from the atmosphere in leaves. Further, there were no significant differences in methane concentrations between in situ and in vitro methods, suggesting that sampling methane from leaves of tall trees in the field was feasible. Elevated temperature caused by an altitude gradient [from 600 m to 300 m (+1.5 ℃) and to 30 m (+3 ℃)] depressed methane emissions from the leaves of four tree species (i.e., Schima superba, Itea chinensis, Syzyglum hancei, and Machilus breviflora), and significant methane absorption was observed at 30 m altitude (with a temperature increase of 3 ℃). Therefore, our study confirms that living plant leaves release or absorb methane in an aerobic environment; however, the methane emission or absorption is limited by plant species and environmental factors (e.g., altitude, temperature). In the future, the list of methane emission from plants should be investigated and environmental factors should be considered to assess accurately the roles that forest ecosystems play as a source or a sink of methane.

Key words: biogenic methane, branch with leaves in situ, branch with leaves in vitro, environmental factors, altitudinal gradient

摘要：

植物能直接释放甲烷（CH₄）一直被质疑。为了验证活体植物的CH₄源汇功能,利用改装的便携式光合仪（Li-6400）采集植物叶片释放的CH₄,并通过气象色谱分析甲烷体积分数,初步研究了14种植物叶片的CH₄排放情况,并比较了原位和离体枝条叶片CH₄排放差异,以及海拔变化对部分植物叶片CH₄排放的影响。结果表明,华南地区14种植物叶片CH₄排放情况随植物种类而异,无忧树（Saraca dives）、树菠萝（Artocarpus heterophyllus）和海南菜豆树（Radermachera hainanensis）的叶片能直接排放CH₄,垂叶榕（Ficus benjamina）则吸收CH₄,其他种类植物则有吸收和排放CH₄的双重现象。而且,原位和离体枝条采集植物叶片排放CH₄的气体浓度没有显著差异,表明离体枝条法采集叶片CH₄排放气体适合野外采样。海拔梯度引起的小幅度增温抑制了被测4种植物叶片的CH₄排放,并在30 m海拔（增温3 ℃）的环境中表现出显著的CH₄吸收。可见,植物叶片在有氧的环境中可直接排放或吸收CH₄,然而其CH₄的释放与植物种类和环境因子（如海拔、温度）密切相关。在今后的植物CH₄排放清单编制时,应充分考虑环境因子对植物CH₄源汇功能的影响,以准确评估森林生态系统的CH₄源汇功能。

关键词: 植物源甲烷, 原位枝条叶片, 离体枝条叶片, 环境因子, 海拔梯度