PARENT SESSION
Poster Session # 15: Plant Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Control of nitrogen uptake responses to elevated CO₂ in tree seedlings.

Silim, Salim¹, Sehtiya, Harbans¹, BassiriRad, Hormoz^*,1, ¹ University of Illinois at Chicago, Chicago, Illinois

ABSTRACT- An important factor that regulates the uptake of nitrogen (N) by plants is the physiological uptake capacity of the root system. A number of studies have shown that kinetics of root N uptake can change dramatically in response to CO₂ enrichment, but the effects are not consistent among species or between inorganic N forms. Theoretical considerations suggest that such inconsistencies must involve changes in: 1) supply of sugars to the root and/or 2) internal N pools i.e., elevated CO₂ elicits species-specific pattern of responses in root carbohydrate and internal N pools. We examined the effects of elevated CO₂ (720 versus 360 Pa) on N uptake and assimilation in seedlings of Acer saccharinum, Fraxinus pennsylvanica and Ulmus americana. Elevated CO₂ significantly increased ammonium uptake in all species, but had little effect on nitrate uptake. Ammonium uptake increased the most in Ulmus followed by Acer and Fraxinus. Total root and leaf soluble carbohydrates were higher under elevated CO₂. The activity of glutamine synthetase, increased significantly in roots of all species under elevated CO₂ while that of nitrate reductase did not. Consequently, in all species root ammonium concentration was significantly lowered at high CO₂. Total root amino acids and nitrate concentration did not respond to growth CO₂. From these data we conclude that ammonium uptake responses to high CO₂ may have been mediated by internal root ammonium concentration and a positive control via root carbohydrate status.

Key words: elevated CO₂, tree seedlings, nitrogen, nitrate reductase