Wetlands are the single largest natural source of methane (CH4). CH4 fluxes in wetlands are highly variable both in space and time due to the presence of distinct plant communities and the relative importance of the different CH4 transport pathways in them. Transport through plants is though as the main transport pathway for CH4 release. Hence the understanding of the mechanisms governing plant transport paramount to improve predictions of feedbacks to climate change from wetlands and for the design of ecosystem-based management strategies that help mitigate such feedbacks. While the physical mechanisms for gas transport are fairly understood, the biological mechanisms are less known remaining largely underrepresented in current models. We investigated the relationship between carbon dioxide (CO2) uptake and CH4 flux in three cosmopolitan wetland plant species. Our goal was to assess the effect of stomata control on CH4 flux and how CH4 and CO2 uptake changed throughout the growing season. Accordingly, we measured the change of CH4 and CO2 concentrations in leaf chambers of cattail (Typha angustifolia), American lotus (Nelumbo lutea), and water lily (Nymphaea odorata) simultaneously. Chambers were deployed three times (June through August). Each deployment consisted of five replicated measurements during three times of the day.
Results/Conclusions
Correlations between CH4 and CO2 uptake were only significant in water lily (r2 = 0.26, p-value <0.001), indicating that stomata regulation was an important control of CH4 flux, while in cattail and American lotus, stomata openness did not control CH4 flux. CH4 flux per leaf area was species-specific, increasing (cattail), decreasing (American lotus) or peaking in July (water lily) throughout the sampling period. CO2 uptake showed similar patterns. When normalizing by leaf area index (LAI), CH4 flux and CO2 uptake in cattail showed a substantial seasonal increase. CH4 flux in August was up to 80 times the fluxes measured in June (0.03 ± 0.001 and 3.1 ± 0.8 µmol m-2_ground s-1 respectively), while CO2 uptake increased 3 times (-9.3 ± 1.7 and -31.3 ± 3.7, respectively). In American lotus and water lily, LAI normalized CH4 fluxes did not showed significant differences during the sampling period (0.3 ± 0.04, 0.5 ± 0.08 µmol m-2_ground s-1, respectively). The specificity in CH4 flux and CO2 uptake, highlights the importance of plant species composition in the spatiotemporal heterogeneity of carbon fluxes in wetlands.