Poster: Nutrient Biology

Abs # 411: C/N Ratios in Four Species of Plants Exposed to Varying Light, Nutrient, Water, and CO₂

Presenter:	Thompson, Jennifer N., jthompso@bradley.edu
Authors	Thompson, Jennifer N. (A)   Bernacchi, Carl J. (A)   Coleman, James S. (B)   McConnaughay, Kelly D.M. (A)
Affiliations:	(A): Bradley University Biology Department, Peoria, IL (B): Desert Research Institute, Reno, NV

Nitrogen concentrations in plant tissues can vary as a function of resource availability. Alterations in nutrient concentrations are thought to reflect changes in whole-plant nitrogen use efficiency (NUE). We have previously argued that CO₂-induced reductions in nitrogen concentration can be attributed to accelerated plant growth rather than a physiological adjustment of NUE. We examined whether other environmentally-induced changes in plant tissue nitrogen concentration may also be explained by altered rates of plant growth and development. Four species of old-field annuals were grown at broadly varying light, nutrient, water, and CO₂ levels. The results of this study show highly variable nitrogen accrual rates across most environmental conditions, but similar patterns of whole-plant nitrogen vs. non-nitrogen biomass accrual, and thus similar NUE, over a wide range of environmental conditions. However, severely light-limited plants showed decreased NUE for 2 of 3 species and severely nutrient-limited plants had increased NUE for all species. Whole-plant nitrogen 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. We conclude that physiological adjustments in NUE are limited to environments with severely limited or overabundant resources.