I examined differences in the biogeochemical cycles of CH4 and CO2 (fluxes, concentrations, production, CH4 oxidation) inTypha latifolia wetlands on silty clay sediment versus organic peat soil in central New York State to determine whether variation in the amount of organic matter in sediment or soil, or plant production on sites with different organic matter content, affected variation in CH4 and CO2. I found very high temporal variation in CH4 within each site, precluding the detection of variation in CH4 as a function of sediment or soil organic matter content. In 1994. CH4 efflux from two peat sites to the atmosphere averaged 7 and 87 nmol m−2s−1 compared to 89 and 408 nmol m−2s−1 compared to 1.02 and 1.65 μmol m−2s−1 for the sediment sites. I assessed the role of plant production by experimentally removingT. latifolia shoots from small plots: this lowered CH4 efflux from the sediment site by 85%, suggesting that plants foster CH4 production in low organic matter sediment, but CH4 efflux was 14-times greater following shoot removal on one peat site. Shoot removal had no effect on CO2 efflux. Variations in temperature, dissolved organic carbon, and pCH4 in sediment or soil porewater explained the variation in CH4 efflux among the four study sites, whereas variation in net primary production explained the variation in CO2 efflux.