PARENT SESSION
Poster Session #63: Late Breaking and Newsworthy Papers.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

C/N ratios in four species of plants exposed to varying light, nutrients, water, and CO₂.

THOMPSON, JENNIFER^*,1, BERNACCHI, CARL², COLEMAN, JAMES³, MCCONNAUGHAY, KELLY¹, ¹ Bradley University, Peoria, IL² University of Illinois, Urbana-Champaign, IL³ Desert Research Institute, Reno, NV

ABSTRACT- Nitrogen concentrations in plant tissues can vary considerably as a function of resource availability. Alterations in nutrient concentrations are thought to reflect changes in whole-plant nitrogen-use efficiency (NUE), with lower tissue nitrogen concentration indicating greater NUE. We have previously argued that CO₂-induced reductions in whole-plant tissue nitrogen concentration can be attributed to accelerated plant growth rather than increased whole-plant NUE. We set out to examine whether other environmentally-induced changes in plant tissue nitrogen content may also be explained by altered rates of plant growth and development rather than by adjustments in NUE. Four species of old-field annuals were grown at broadly varying light, nutrient, water, and CO₂ levels. Plants were sequentially harvested and tissues were bulked, dried, and sub-sampled. C/N determinations were made by combustion and elemental analysis. Statistical analyses of N vs. non-N biomass allometries revealed that most environments showed similar patterns of N vs. non-N biomass accrual (and thus similar NUE). However, severely light-limited plants had decreased NUE for 2 of 3 species and severely nutrient-limited plants had increased NUE for all species. Whole-plant N accrual increased and NUE concomitantly decreased under saturating water for 2 of 3 species. A marginally-significant, modest increase in NUE was found at high CO₂ levels for 2 of 4 species. In conclusion, whole-plant NUE does not vary greatly as a function of resource availability, except in cases of extreme resource limitation.

KEY WORDS: NUE, C/N, allometry, resource availability