Evaluation of a closed-chamber method for estimating methane emissions from aquatic plants

Abstract

Closed-flow chambers are commonly used to measure CH 4 emissions from aquatic plants. We monitored environmental and plant physiological responses to closed chambers during measurements of CH 4 emission from Typha latifolia (cattails) to evaluate potential errors in emission estimates. In 1990, two wetlands were studied: one in NE Kansas and one in central New York. Leaves and stems of Typha enclosed in gas-impermeable, collapsible bags were exposed to rapid increases in chamber air temperature and, thus, tissue temperatures (up to 9 °C above ambient) as well as rapid reductions in both CO 2 partial pressure due to photosynthesis and the leaf-to-air water vapor pressure deficit due to transpiration. These rapid (< 5 min) environmental changes within chambers are known to affect stomatal aperture through which CH 4 exits Typha leaves. Indeed, stomatal conductance ( g ) increased up to 42% compared to control leaves after 19 min of enclosure in chambers, and chamber effects on interactions between irradiance and g were detected. The duration of enclosure also critically affected the CH 4 gradient within chambers. Estimated CH 4 emission from leaves in chambers sampled after 19 min (3 nmol m -2 s -1 ) was 10-fold lower than estimates based on 30-s sampling periods (30 nmol m -2 s -1 ) due to reduction in the leaf-to-air concentration gradient for CH 4 . Since closed chambers (1) induce alterations in g, (2) may result in rapid environmental changes, and (3) lead to almost instantaneous reductions in the leaf-to-air concentration gradient for CH 4 diffusion, we suggest that only very short enclosure times should be used when measuring CH 4 emission from plants. DOI: 10.1034/j.1600-0889.1992.00006.x