植物释放甲烷研究进展

Methane emissions from plants:a review

植物是否在有氧条件下自身产生甲烷、其产生机制和释放速率等问题目前还存在很大争议,如果确证植物在有氧条件下产生较大量的甲烷,就必须重新认识和计算全球甲烷的源汇及其收支平衡。已有研究表明,植物排放的甲烷有一部分是由土壤或木本植物的根和树干内部产甲烷微生物产生,再通过植物传输进入大气中的;植物本身产生甲烷的机制可能主要是在活性氧自由基的作用下,将植物细胞壁成分果胶、木质素等中的甲氧基转化为甲烷,这一过程受到高温、强光和UV辐射等环境胁迫的刺激。根据植物排放速率或大气甲烷浓度与碳同位素组成的实测值,对区域和全球植物源甲烷排放率做出的估算还存在相当大的不确定性,需要对更多植物和更多地点开展实测研究,深入了解植物产甲烷的机制和过程,并结合大气传输模型才能进一步提高估算准确性。

The pioneering work by Keppler＇s group on large aerobic methane production from plants（AMP）made it an urgent requirement to re-evaluate atmospheric methane sinks and sources and its global budget.However,there is still considerable controversy on the existence of AMP,the underlying mechanisms and its emission rate.Recent researches demonstrated that a fraction of methane emitted from plants is actually produced by methanogenic archaea in soil or/and in the anaerobic tissues of roots and trunks of woody plants.Plants transport methane to the atmosphere by molecular diffusion and pressure-difference-driven convective flow.There are also evidences that methane produced in plants is probably through reactive oxygen species（ROS）,which generates methane from methoxyl groups in pectin,lignin and other cell wall constituents.Since ROS production is stimulated by environmental stresses,higher AMP was expected and has been observed under high temperature,intense light,UV radiation and other stress conditions.The estimated emission rate of phytogenic methane,either by extrapolation from leaf level measurement or by nverse analysis based on atmospheric methane concentration and carbon isotope composition monitoring,varies largely in different biomes at regional and global scales.Further field studies covering more species and communities are needed toimprove the estimation of aerobic methane emission rate and evaluation of global CH4 budget,as well as to deepen our understanding of AMP mechanisms.