Methane emission to the atmosphere through emergent cattail (Typha latifolia L.) plants

Methane (CH₄) produced microbially in sediments of marshes is emitted to the atmosphere primarily by flowing through and out of emergent aquatic plants. The magnitude of such emission rates and factors controlling those rates are not well understood. We evaluated CH₄ emission from the widely distributed aquatic emergent plant cattail (Typha latifolia L.) in several wetlands in the United States using a field gas-exchange system that concurrently estimated stomatal aperture (i.e., conductance) on the surface of leaves and net photosynthesis. We compared gas exchange among plants of different age and from sites with different soil and atmospheric conditions. The mean rate of CH₄ emission was 0.22 μ mol m^-2 [leaf] s^-1, which is 940 mg CH₄ m^-2 d^-1 on a ground-area basis, with individual rates ranging from 0.01 to 1.49 μmol m^-2 [leaf] s^-1. For individual plants, we found emission rates were (i) highest for the part of the leaf about 1.0 m above the waterline and lower near the leaf tip and close to the leaf base, and (ii) highest near midday and lower soon after sunrise and towards sunset. We also found the ease that CH₄ moves in a sediment-plant-atmosphere continuum seems to increase with plant age. We propose that a series of factors influences CH₄ emission from Typha latifolia to the atmosphere; stomatal conductance and plant age are as important as the amount of microbially produced CH₄ in the wetland sediment.