Controlling Factors of Seasonal Variation of Stem Methane Emissions From Alnus japonica in a Riparian Wetland of a Temperate Forest
Controlling Factors of Seasonal Variation of Stem Methane Emissions From Alnus japonica in a Riparian Wetland of a Temperate Forest
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DOI：
10.1029/2021jg006326
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发表时间：
2021-10
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影响因子：
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通讯作者：
Ayaka Sakabe;Kenshi Takahashi;W. Azuma;Masayuki Itoh;M. Tateishi;Y. Kosugi
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作者：
Ayaka Sakabe;Kenshi Takahashi;W. Azuma;Masayuki Itoh;M. Tateishi;Y. Kosugi
树木介导的甲烷 (CH4) 排放代表了森林生态系统释放的总 CH4 通量的不确定途径。我们使用自动化室测量了 2017 年至 2018 年温带森林河岸湿地中桤木茎 CH4 通量。茎 CH4 通量随季节变化，显示夏季最大值和冬季最小值。秋季、冬季、春季和夏季茎 CH4 通量的中位数分别为 12.9、0.5、0.4 和 13.4 nmol m−2 s−1。树下地下水中溶解的CH4浓度是茎CH4通量的主要控制因素。土壤环境条件（温度和地下水位）的时间变化控制了地下水中溶解的 CH4 浓度，从而控制了 CH4 通量。此外，当落叶期间树液通量减少时，观察到茎 CH4 排放。这些结果表明根际CH4主要通过树木的细胞间隙以气态形式运输。强降雨偶尔会导致茎 CH4 排放量短暂增加，这是由于降雨影响地下 CH4 浓度而导致地下水流路发生暂时变化。我们的研究结果强调需要进行连续的茎 CH4 通量测量，以更好地了解森林中 CH4 动态对气候变化的控制因素和未来响应。
Tree‐mediated methane (CH4) emissions represent an uncertain pathway of the total CH4 flux released from forested ecosystems. We measured the stem CH4 fluxes from Alnus japonica in a riparian wetland of a temperate forest for a year from 2017 to 2018, using automated chambers. The stem CH4 fluxes varied seasonally, showing summertime maxima and wintertime minima. Medians of stem CH4 fluxes were 12.9, 0.5, 0.4, and 13.4 nmol m−2 s−1 during autumn, winter, spring, and summer, respectively. Dissolved CH4 concentration in groundwater beneath the trees was the major controlling factor of the stem CH4 fluxes. Temporal variations in soil environmental conditions (temperature and groundwater level) controlled dissolved CH4 concentrations in groundwater, and accordingly, stem CH4 fluxes. In addition, stem CH4 emissions were observed when the sap flux diminished during the defoliation period. These results indicate that CH4 in the rhizosphere is mainly transported in the gaseous form through intercellular space in trees. Intense rainfall occasionally caused a transient increase in the stem CH4 emissions, which was attributed to the temporal changes in the groundwater flow paths by rainfall affecting the belowground CH4 concentrations. Our findings highlight the need for continuous stem CH4 flux measurements for improved understanding of the controlling factors and future response of CH4 dynamics in forests, with regards to climate change.