Control of the diurnal pattern of methane emission from emergent aquatic macrophytes by gas transport mechanisms

Methane emissions from Typha latifolia L. showed a large mid-morning transient peak associated with rising light levels. This peak was also associated with a steep decline in lacunal CH4 concentrations near the stem base. This pattern contrasted sharply with emissions from Peltandra virginica (L.) Kunth that gradually rose to a peak in the mid-afternoon, corresponding to elevated air temperatures. Internal CH4 concentrations within P. virginica stems did not change significantly over the diurnal period. Stomatal conductance appeared to correlate directly with light levels in both plant types and were not associated with peak CH4 emission events in either plant. These patterns are consistent with a convective throughflow and diffusive gas ventilation systems for Typha and Peltandra, respectively. Further effects of the convective throughflow in T. latifolia were evident in the elevated CH4 concentrations measured within brown leaves as contrasted to the near ambient levels measured within live green leaves. Experimental manipulation of elevated and reduced CO2 levels in the atmosphere surrounding the plants and of light/dark periods suggested that stomatal aperture has little or no control of methane emissions from T. latifolia.