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Regulation of Growth and Photosynthetic Performance in Elodea canadensis in Response to Inorganic Nitrogen

T. V. Madsen and A. Baattrup-Pedersen
Functional Ecology
Vol. 9, No. 2 (Apr., 1995), pp. 239-247
DOI: 10.2307/2390570
Stable URL: http://www.jstor.org/stable/2390570
Page Count: 9
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Regulation of Growth and Photosynthetic Performance in Elodea canadensis in Response to Inorganic Nitrogen
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Abstract

1. Many submerged aquatic macrophytes posses inducible biochemical or biophysical mechanisms that can enhance the internal inorganic carbon concentration above that which can be achieved by diffusive uptake of CO2 coupled with C-3 photosynthesis. 2. The Possible interaction between nitrogen economy and use of a carbon concentrating mechanism was studied in Elodea canadensis, which has a mechanism based on bicarbonate usage. The nitrogen content of the plants was varied from ∼ 800 to ∼ 3500 μmol N g-1 DOW by growing them in hydroponic cultures at a range of inorganic nitrogen concentrations. 3. The relative growth are increased with increasing tissue-N from 0.020 day-1 at 800 μmol N g-1 DW to 0.045 day-1 at 1600 μmol N g-1 DW. The photosynthetic performance of the plants was also affected by tissue-N. The photosynthetic capacity increased from 172 to 465 μmol CO2 g-1 DW h-1 and the HCO-3 uptake capacity from 63 to 310 μmol Cg-1 DWh-1 with increasing tissue-N. The CO2 conductance, a measure of CO2 affinity, increased four times and the bicarbonate conductance 10 times. 4. High nitrogen concentrations are required in Elodea to maintain an efficient carbon-assimilation apparatus and an efficient carbon-concentrating mechanism. 5. The interdependence of nitrogen-use efficiency for photosynthesis (PNUE) and nitrogen content was dependent on the inorganic carbon concentration at which PNUE was measured. PNUE measured at saturating inorganic carbon concentrations declined with increasing tissue-N, presumably as a result of increased allocation of nitrogen into non-photosynthetic pools at high tissue-N. In contrast, PNUE increased with increasing tissue-N when measured at sub-saturating inorganic carbon concentrations. 6. The total Rubisco activity was positively correlated with tissue-N in Elodea and was substantially higher than the photosynthetic capacity indicating that Rubisco may not play a primary role in regulating the photosynthetic capacity of Elodea. Rather, it may have a role in regulating photosynthesis at low inorganic carbon concentrations, as suggested by the observed linear relationship between CO2 conductance and Rubisco.

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