5:15 PM - 6:30 PM
[ACG37-P03] Seasonal variation and controlling factors of stem methane emissions from Alnus japonica revealed by continuous measurements
Keywords:Stem methane emission, Alnus japonica, closed chamber
Recent studies suggest that tree-mediated methane emissions have the potential to offset the soil methane sink and may convert the forest from a net sink to a net source. However, tree-mediated CH4 emissions represent an uncertain pathway of the total CH4 flux from forested ecosystems. We measured the stem CH4 fluxes from Alnus japonica in a riparian wetland of a temperate forest for a year using automated chambers. Three mature Alnus japonica trees grown naturally in the riparian wetland were selected for this study. Dissolved CH4 concentrations in groundwater at two depths beneath each tree were measured biweekly. The sap flux for each tree was measured with Granier-type sensors.
The stem CH4 fluxes seasonally vary, showing summertime maxima and wintertime minima. The stem CH4 fluxes positively correlate with dissolved CH4 concentration in groundwater beneath the trees. 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 transported in the gaseous form through intercellular space in trees. On the other hand, CH4 transport by sap flux also likely exists based on our observations; stem CH4 fluxes showed diurnal variation. We also observed that rainfall caused a clear increase in the stem CH4 emissions. Temporal changes in the groundwater flow paths by rainfall would have affected the belowground CH4 concentrations and the stem CH4 flux. Dynamic changes in soil environmental conditions (soil temperature, groundwater flow) controlled dissolved CH4 concentrations in groundwater, thus, stem CH4 flux. Our findings highlight the need for continuous stem CH4 flux measurements to better understand the controlling factors and future response of CH4 dynamics in forests to climate change.
The stem CH4 fluxes seasonally vary, showing summertime maxima and wintertime minima. The stem CH4 fluxes positively correlate with dissolved CH4 concentration in groundwater beneath the trees. 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 transported in the gaseous form through intercellular space in trees. On the other hand, CH4 transport by sap flux also likely exists based on our observations; stem CH4 fluxes showed diurnal variation. We also observed that rainfall caused a clear increase in the stem CH4 emissions. Temporal changes in the groundwater flow paths by rainfall would have affected the belowground CH4 concentrations and the stem CH4 flux. Dynamic changes in soil environmental conditions (soil temperature, groundwater flow) controlled dissolved CH4 concentrations in groundwater, thus, stem CH4 flux. Our findings highlight the need for continuous stem CH4 flux measurements to better understand the controlling factors and future response of CH4 dynamics in forests to climate change.