We measured the flow of methane in Typha latifolia L.
(cattail)-dominated wetlands from microbial production
in anoxic sediment into, through, and out of emergent T.
latifolia shoots (i.e. plant transport). The purpose was
to identify key environmental and plant factors that might
affect rates of methane efflux from wetlands to the
Earth's atmosphere. Methane accumulated in leafy T. latifolia
shoots overnight, reaching concentrations up to
10000 μl l−1 (vs. atmospheric concentrations
<4 μl l−1), suggesting that lower stomatal conductance
at night limits
methane efflux from the plant into ambient air. Daytime light
and (or) lower atmospheric humidity that induce
convective gas flow through the plant coincided with (a) an
increase in the rate of methane efflux from T. latifolia
leaves to ambient air (from <0·1 to >2·0 μmol m−2
(leaf) s−1) and (b) a decrease in shoot methane
concentration
to <70 μl l−1. Very short fluctuation in stomatal
conductance during the day did not affect the methane efflux rate
unless, possibly, the rate of photosynthesis decreased. A strong
relationship between the maximum daily rate of
methane efflux and shoot methane concentration (measured before
the onset of convective gas flow) suggests T.
latifolia plants behave like a capacitor (filling with methane
at night, emitting the stored methane during the day).
Experimentally cutting leaves (to prevent pressurization)
reduced plant capacitance for methane.