METHANE STABLE ISOTOPIC DISTRIBUTIONS AS INDICATORS OF GAS-TRANSPORT MECHANISMS IN EMERGENT AQUATIC PLANTS

Methane stable isotope distribution patterns vary markedly between pla nts utilizing convective throughflow ventilation relative to those whi ch primarily employ molecular diffusion. In diffusive plants, methane sampled from lacunal air was C-13-enriched by 10.6 +/- 3.7 parts per t housand relative to sedimentary CH4. In plants possessing the convecti ve flow system, differences between plant lacunal methane collected in daylight and sediment methane were not apparent, and averaged -0.9 +/ - 2.1 parts per thousand. At night, as convection gave way to molecula r diffusion, the isotopic distributions in Typha domingensis Pers. and Typha latifolia L., convective-flow plants, became similar to distrib utions observed in diffusive plants, with plant lacunal methane becomi ng C-13-enriched. Diurnal variations in the isotopic signature of meth ane emitted from Typha were also observed; methane is emitted in dayli ght was C-enriched by 4 - 7 parts per thousand relative to night emiss ions. The results indicate that methane isotopic distributions are use ful indicators of plant gas transport mechanisms. Diurnal variation in isotopic distribution patterns confirm observations that plants with convective throughflow ventilation switch to molecular diffusion in th e absence of sunlight.