PARENT SESSION
Poster Session #45: Elevated CO₂ I.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Extending growth analysis to include water and nitrogen use efficiency at ambient and elevated CO₂.

Peterson, Andrew^*,1, Chrusciel, Tim¹, Harris, Jon¹, Hayashi, Masanobu¹, Jain, Sonal¹, Vitkay, Karen¹, ¹ Columbia University, Oracle, Arizona

ABSTRACT- We present an extension of plant growth analysis in which the net assimilation rate (NAR, biomass gain/leaf area) is partitioned into the product of water use efficiency (WUE, biomass gain/water transpired) and transpiration, and into the product of nitrogen use efficiency (NUE, biomass gain/N in leaves) and N/leaf area (N_area). This extension provides a powerful analytical method for understanding how changes in these four important physiological variables affect the relative growth rate (RGR) of plants. We applied this new analysis to a factorial experiment on wheat (Triticum aestivum) grown at three CO₂ levels and 15 and 25°C. Path analysis revealed complex relationships among these variables that were not apparent using conventional linear models. Elevated CO₂ increased WUE at 15°C but not at 25°C, and had no effect on transpiration at 15°C but reduced transpiration at 25°C. Increasing CO2 also increased NUE without affecting N_area at 15°C, but had no effect on either at 25°C. CO₂ had a negative effect on leaf area ratio (LAR, leaf area/plant mass) at 15°C and a positive effect at 25°C. WUE, transpiration, NUE and N_area all had positive direct effects on NAR at all CO₂ levels and temperatures, as did NAR and LAR on RGR. However, complex negative correlations between LAR, WUE and transpiration, and between LAR, NUE and N_area resulted in no net effect of CO₂ or temperature on the RGR of these plants.

KEY WORDS: growth analysis, water use efficiency, nitrogen use efficiency, elevated CO₂