Thu, Aug 18, 2022: 5:00 PM-6:30 PM
ESA Exhibit Hall
Background/Question/Methods: Methane (CH4) has received increasing attention in climate mitigation due to its rapid recent increase combined with relatively short residence in the atmosphere. Forest ecosystems on well-drained soils are an important global sink for CH4. While it has been assumed that essentially all CH4 uptake by forests is attributable to methanotrophic microorganisms in the upper soil horizons, the same taxa of methanotrophs have been detected in leaf tissues. Prior assessments of foliar methane flux have been few and ambiguous, with accuracy limited by available methods. We conducted surveys of foliar CH4 flux in both upland and lowland (periodically inundated) forest site in central Ontario using a gas analyzer based on off-axis integrated cavity output spectroscopy and a pressure equilibrated chamber system for measurements under a range of light conditions and matching foliar flux measurements to local soil flux. We predicted that foliar CH4 uptake would be detectable in areas where soil was a CH4 sink, ensuring that methanotrophic bacteria were present and that any foliar CH4 sink would not be offset by dissolved CH4 flux through the xylem stream. In addition, we expected that shading of leaves would reduce uptake, consistent with methanotrophic bacterial presence as endophytes within leaf tissue.
Results/Conclusions: Foliar CH4 uptake was pervasive in upland sites where soil was also a CH4 sink. Estimated foliar CH4 uptake in sunlit conditions average 0.54 nmol m-2 s-1, substantially exceeding the detection limit of the system (~0.02 nmol m-2 s--1). In contrast in lowland sites with inundated soils showed leaves were a net source of CH4. Foliar CH4 flux varied substantially among species but was generally higher in broadleaf trees than conifers. Foliar CH4 uptake was also reduced by shading of leaves and in nighttime measurements. An estimate of stand-level foliar uptake, made using local leaf area index estimates, suggests that foliar uptake is ~38% of total soil uptake. The results suggest that foliar CH4 uptake is widespread and quantitatively important - and more broadly imply that the total terrestrial sink for atmospheric CH4 may be substantially underestimated.
Results/Conclusions: Foliar CH4 uptake was pervasive in upland sites where soil was also a CH4 sink. Estimated foliar CH4 uptake in sunlit conditions average 0.54 nmol m-2 s-1, substantially exceeding the detection limit of the system (~0.02 nmol m-2 s--1). In contrast in lowland sites with inundated soils showed leaves were a net source of CH4. Foliar CH4 flux varied substantially among species but was generally higher in broadleaf trees than conifers. Foliar CH4 uptake was also reduced by shading of leaves and in nighttime measurements. An estimate of stand-level foliar uptake, made using local leaf area index estimates, suggests that foliar uptake is ~38% of total soil uptake. The results suggest that foliar CH4 uptake is widespread and quantitatively important - and more broadly imply that the total terrestrial sink for atmospheric CH4 may be substantially underestimated.