|Singsaas, Eric - UNIV OF ILL URB-CHAMPAIGN|
|Delucia, Evan - UNIV OF ILL URB-CHAMPAIGN|
Submitted to: Ecological Society of America Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 20, 2000
Publication Date: N/A
Technical Abstract: Photosynthesis responds to elevated CO2 by reducing investment in carbonreduction enzymes. Theoretically, this investment should lead to greater investment in other resources that limit photosynthesis such as lightharvesting apparatus. This response may be modified in plants exposed to elevated CO2 for several years as soil nutrients may become more limiting. Using gas exchange measurements, we investigated the relationship between photosynthetic light harvesting and carbon reduction in saplings of Liquidambar styraciflua L. growing in the understory of a pine forest. The light limited quantum yield was stimulated in plants grown at elevated CO2, but when measured under at the same ambient CO2 concentration, the quantum yield was the same in both groups. Lightsaturated photosynthesis rates were 3050 percent higher in plants grown at high CO2. This stimulation was maintained when plants were measured under the same CO2 levels, but was much lower (12 percent) when photorespiration was reduced by making measurements at 2 percent O2. Plants at elevated CO2 also had a decreased apparent rubisco carboxylation efficiency (Vc, max) while maximum electron transport rate (Jmax) was unchanged. We conclude that the savings in nitrogen from reduced rubisco concentration at elevated CO2 is not reinvested in other processes. Therefore the primary benefits of elevated CO2 for understory plants are the decrease in photorespiration which increases lightuse efficiency and the decreased rubisco content which increases nitrogenuse efficiency.