ASPECTS OF METHANE FLOW FROM SEDIMENT THROUGH EMERGENT CATTAIL (TYPHA-LATIFOLIA) PLANTS

We measured the flow of methane in Typha latifolia L. (cattail)-domina ted wetlands from microbial production in anoxic sediment into, throug h, and out of emergent T. latifolia shoots (i.e. plant transport). The purpose was to identify key environmental and plant factors that migh t affect rates of methane efflux from wetlands to the Earth's atmosphe re. Methane accumulated in leafy T. latifolia shoots overnight, reachi ng concentrations up to 10000 mu l l(-1) (vs. atmospheric concentratio ns < 4 mu l l(-1)), suggesting that lower stomatal conductance at nigh t limits methane efflux from the plant into ambient air. Daytime light and (or) lower atmospheric humidity that induce convective gas flow t hrough 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 p mol m(-2) (leaf) s(-1)) and (b) a decrease in shoot methane concentrat ion to < 70 mu l l(-1). Very short fluctuation in stomatal conductance during the day did not affect the methane efflux rate unless, possibl y, the rate of photosynthesis decreased. A strong relationship between the maximum daily rate of methane efflux and shoot methane concentrat ion (measured before the onset of convective gas flow) suggests T. lat ifolia plants behave like a capacitor (filling with methane at night, emitting the stored methane during the day). Experimentally cutting le aves (to prevent pressurization) reduced plant capacitance for methane .