Ebullitive release of lacunar gases from floral spikes of Potamogeton angustifolius and Potamogeton amplifolius: Effects on plant aeration and sediment CH4 flux

Field and laboratory studies examined two Potamogeton species (P. angustifo lius Berchtold Presl. and P. amplifolius Tuckerm.) for effects of ebullitio n from submersed floral inflorescences, or spikes, upon plant aeration and sediment CH4 release. Results indicated that daytime release of lacunar gas via ebullition from submersed floral spikes of mature clones was light-dep endent and comparable to post-emergence flux. Analysis of tracer movement t hrough plants and measurements of lacunar pressure revealed that daytime co nvection was driven by a sustained pressure difference (3-6 kPa at midday) between non-ebullient and ebullient clones, and enhanced exchange of lacuna r gas between clones connected via rhizome. In comparison to non-ebullient clones, stem lacunae of ebullient clones showed higher concentrations of CH 4 and CO2 and lower concentrations of O-2. In situ measurements of diffusiv e and ebullitive CH4 flux from plants and sediment showed that ebullitive r elease from submersed floral spikes of P. angustifolius represented 19-29% of total areal CH4 flux. This indicates that, in addition to effects on pla nt aeration, ebullitive release of lacunar gases from submersed rhizomatous angiosperms may represent a heretofore-unquantified source of CH4 emission from aquatic systems. (C) 2001 Published by Elsevier Science B.V.