Abstract：
Plant-mediated CH4 transport (PMT) is the dominant pathway through which soil-produced CH4 can escape into the atmosphere and thus plays an important role in controlling ecosystem CH4 emission. PMT is affected by abiotic and biotic factors simultaneously, and the effects of biotic factors, such as the dominant plant species and their traits, can override the effects of abiotic factors. Increasing evidence shows that plant-mediated CH4 fluxes include not only PMT, but also within-plant CH4 production and oxidation due to the detection of methanogens and methanotrophs attached to the shoots. Despite the inter-species and seasonal differences, and the probable contribution of within-plant microbes to total plant-mediated CH4 exchange (PME), current process-based ecosystem models only estimate PMT based on the bulk biomass or leaf area index of aerenchymatous plants. We highlight five knowledge gaps to which more research efforts should be devoted. First, large between-species variation, even within the same family, complicates general estimation of PMT, and calls for further work on the key dominant species in different types of wetlands. Second, the interface (rhizosphere-root, root-shoot, or leaf-atmosphere) and plant traits controlling PMT remain poorly documented, but would be required for generalizations from species to relevant functional groups. Third, the main environmental controls of PMT across species remain uncertain. Fourth, the role of within-plant CH4 production and oxidation is poorly quantified. Fifth, the simplistic description of PMT in current process models results in uncertainty and potentially high errors in predictions of the ecosystem CH4 flux. Our review suggest that flux measurements should be conducted over multiple growing seasons and be paired with trait assessment and microbial analysis, and that trait-based models should be developed. Only then we are capable to accurately estimate plant-mediated CH4 emissions, and eventually ecosystem total CH4 emissions at both regional and global scales.
摘要：
植物介导的CH4运输（PMT）是土壤产生的CH4逃逸到大气中的主要途径，因此在控制生态系统CH4排放中起着重要作用。PMT同时受到非生物和生物因素的影响，以及生物因素的影响，如优势植物物种及其性状，可以超越非生物因素的影响。越来越多的证据表明，植物介导的CH4通量不仅包括PMT，而且由于检测到附着在芽上的产甲烷菌和甲烷营养菌，植物内CH4的产生和氧化。尽管物种间和季节间存在差异，以及植物内微生物对总植物介导的CH4交换（PME）的可能贡献，当前基于过程的生态系统模型仅根据连生植物的整体生物量或叶面积指数估算PMT。我们强调了五个知识差距，应该投入更多的研究工作。首先,物种间差异很大，即使在同一个家庭里，使PMT的一般估计复杂化，并呼吁进一步研究不同类型湿地的关键优势物种。第二,界面(根际-根，根茎,或叶片大气）和控制PMT的植物性状记录不佳，但需要从物种到相关功能组的概括。第三，PMT跨物种的主要环境控制仍不确定。第四，植物内CH4产生和氧化的作用定量不佳。第五,当前过程模型中对PMT的简单描述导致生态系统CH4通量预测的不确定性和潜在的高误差。我们的审查表明，通量测量应在多个生长季节进行，并与性状评估和微生物分析配对，应该开发基于特征的模型。只有这样，我们才能准确估计植物介导的CH4排放量，最终在区域和全球尺度上的生态系统总CH4排放量。
