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Title: SEDIMENT AS A CARBON SOURCE FOR THE SUBMERSED MACROPHYTE VALLISNERIA

Author
item KIMBER, A - IOWA STATE UNIVERSITY
item CRUMPTON, W G - IOWA STATE UNIVERSITY
item Parkin, Timothy
item SPALDING, M H - IOWA STATE UNIVERSITY

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: It is well recognized that wetlands are efficient at filtering nutrient runoff from agricultural lands. A primary mechanism for this nutrient removal is uptake by aquatic plants. Thus, an increase in the growth of the aquatic plants may lead to increased efficiency of nutrient uptake in such systems. One factor controlling the growth of submersed aquatic plants is availability of carbon dioxide. In this study we investigated the source of carbon dioxide used in photosynthesis by the submersed plant, Vallisneria. We found that most of the carbon dioxide taken up by the plant came from the sediments, where it was produced as the result of bacterial decomposition processes. In addition we observed that the plant could store this sediment derived carbon dioxide in intercellular gas spaces in the stem and leaves. These findings suggest that increasing bacterial activity in the sediments may increase the growth rate of the aquatic plants and increase the filtering capacity of wetlands. This finding may represent a new avenue of exploration for scientists searching for ways to improve the performance of wetland systems.

Technical Abstract: Carbon assimilation by submersed macrophytes is potentially limited by low CO2 availability. Since sediment CO2 concentrations are typically much higher than water column concentrations, a strategy for sediment CO2 assimilation would be advantageous. The network of interconnected lacunae in macrophytes provides a pathway and reservoir for CO2 that may come from the sediments. We report very high concentrations of CO2 in leaf lacunae of the submersed macrophyte Vallisneria that do not vary with light/dark cycles, (in contrast to diurnal changes in internal O2 concentrations). The gradient of CO2 concentration from leaf base to leaf tip is similar to the gradient in CH4 concentration and opposite to the gradient in O2 concentrations in the same leaf samples, suggesting influx of CO2 and CH4 from the sediments. Further, plants grown in sediments with contrasting isotopic carbon values have leaf and lacunar gas isotopic carbon values that reflect the isotopic carbon value of sediment pore-water rather than the water column and indicate that the majority of carbon fixed is sediment-derived.