Utilization of Sediment CO2 by Selected North American Isoetids

The photosynthetic uptake of root-zone CO₂ was determined forEriocaulon septangulare, Gratiola aurea, Isoetes macrospora,Littorella uniflora var. americana and Lobelia dortmanna aspart of a study of the photosynthetic carbon economy of submergedaquatic isoetids. The pH and dissolved inorganic carbon (DIC)of the sediment interstitial water in four Wisconsin lakes reflectedthe water column character, where the DIC increased with depthin the sediment to concentrations five to ten times those ofthe water column. Sediment free CO₂ concentrations were 5–50times those in the water column and were similar at all sites(about 05–1.0mM CO₂ in the root-zone). In ‘pH-drift’studies these plants were unable to take up HCO₂^–. Laboratory determinations of the carbon uptake from the rootand shoot-zones were made for all five species. These experimentsshowed that CO₂ in the root-zone accounted for 65–95 percent of external carbon uptake for the five species. For G.aurea and E. septangulare, root-zone CO₂ was > 85 per centof carbon uptake. Carbon, CO₂, photosynthesis, sediment, isoetid, Eriocaulon septangulare, Gratiola aurea, Isoetes macrospora, Littorella uniflora, Lobelia dortmanna