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Research advancement in the processes and mechanisms of transporting methane by emerged herbaceous plants and hygrophytes |
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| Affiliation: | Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China and School of Geographic and Environmental Sciences, Tianjin Normal University, Tianjin 300387, China |
| Abstract: | Methane (CH4) is an important greenhouse gas, and is involved in atmospheric chemical reactions. Aquatic and hydric environments are important sources of atmospheric CH4. Majority of CH4 are transported and released to atmosphere by emerged herbaceous plants and hygrophytes in aquatic and hydric environments. In recent decades, there has been increasing attention on how plants transport CH4. During CH4 transportation processes, several interfaces of CH4 exchange play important roles. First, the tips of lateral roots are primary locations (hotspots) for CH4 entering the root systems and regulate the gross CH4 transportation. Then, the diaphragms in the aerenchyma and the root collar impose great resistances for the overall CH4 transportation processes. In early studies, it was controversial that whether CH4 emission from plants to atmosphere was controlled by stomas or micropores (small cracks and holes in aboveground part of plant except the blade). Recent studies have confirmed the dominant role of micropores for CH4 transportation and emission. The dead and damaged stems are widely considered to have positive effects on CH4 transportation. Diffusion and convection are the two main transporting mechanisms of CH4, with the efficiency of convection being generally higher than that of diffusion. Both biological (e.g. biomass and photosynthesis) and environmental (e.g. light, temperature and humidity) factors regulate the CH4 transportation. Many studies have contributed to understanding the CH4 transportation processes and mechanisms by emerged herbaceous plants and hygrophytes. However, there are still some questions needing further investigations. Issues of consideration may include the operational efficiency in the critical interfaces of CH4 exchange, the plant parts that play a decisive role in the entire CH4 transportation, the underlying roles of diffusion and convection on CH4 interfaces exchanges and entire long distance transports, the combined and coupling effects and mechanisms of biotic and abiotic factors, and the similarities and differences of CH4 transporting processes and mechanisms among plant species. |
| Keywords: | Methane transportation, aerenchyma, convection, aquatic plants, wetland plants, greenhouse gases |
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