芦苇植株对湿地温室气体排放的影响及其日变化特征

Effect of Vegetation on Greenhouse Gases Emission from Phragmitesaustralis in the Yangtze River Estuary in Summer and Its Diel Variation

利用静态箱-气相色谱法对夏季（7月、8月和9月）长江河口湿地芦苇植被CO2、CH4和N2O的叶面通量、茎秆扩散速率以及沉积物通量的日变化进行研究。结果显示,通过芦苇叶片排放的N2O与CH4的量分别为2.99μg/（m2·h）和15.36μg/（m2·h）,CO2则呈现白天吸收（-120.86 mg/（m2·h））、夜间排放（69.39 mg/（m2·h））的特点。芦苇茎秆N2O、CH4和CO2平均扩散速率分别为1.96μg/h、142.45μg/h和10.69 mg/h,沉积物平均排放通量为N2O 8.18μg/（m2·h）、CH41.58 mg/（m2·h）、CO2169.66 mg/（m2·h）。芦苇茎秆和沉积物界面CH4和CO2的排放均呈现出明显的＂单峰型＂昼夜变化规律,其排放峰值集中在日照及温度最高的9：00至15：00。芦苇植株是影响温室气体排放变化的因素之一。芦苇植株在光合作用下吸收CO2并促进CH4的排放,而芦苇发达的根系及茎秆是温室气体排放的主要途径。同时,Pearson相关性分析表明温度对芦苇群落CH4和NO2的排放影响显著,但与CO2通量的相关性不明显。土壤氧化还原电位对3种气体的排放均有显著影响。

The static closed chamber-chromatograph method was used to investigate the diel variation of three greenhouse gases ＇（ N2O,CH4 and CO2） fluxes from reed（ Phragmites australis） in the Yangtze River estuary in summer. Results indicate that N2O and CH4 fluxes from reed leaves are relatively low compared to the CO2 flux,and the average CO2 fluxes are-120. 86 mg/（ m2·h） and69. 39 mg/（ m2·h） for daytime and night,respectively. Photosynthesis and respiration of reed plant are the main cause of its diel variation. Average diffusion rates of CH4 and CO2 from reed stem are 142. 45 μg/h and 10. 69 mg/h,respectively while the stem N2O flux is still low（ 1. 96 μg/h） because of the shortage and limitation of nitrogen in sediment. Fluxes of N2O,CH4 and CO2 from sediment are8. 18 μg/（ m2·h）,1. 58 mg/（ m2·h） and 169. 66 mg/（ m2·h）,respectively. Diel variation of CH4 and CO2 fluxes from reed stem is characterized by ＂single peak type＂. The peak of CH4 and CO2 emission usually appears between sunrise and noon when the sunlight is strong. The reed plant itself makes great contribution to greenhouse gases emission. The photosynthesis of Phragmites australis can stimulate production and transpiration of methane promptly. The developed aerenchyma of Phragmites australis is an important channel for the gases to transport into atmosphere. According to Pearson correlation analysis,temperature is the main factor of N2O and CH4 fluxes from reed stem,and all three gases＇ fluxes are significantly correlated with sediment redox potential.