PARENT SESSION
Poster Session #11: Elevated CO₂.
Monday, August 6, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Utilization of amino acids by tree seedlings and its potential influence on growth responses to elevated CO₂.

Silim, Salim¹, BassiriRad, Hormoz ¹, ¹

ABSTRACT- Interspecific variability in acquisition and assimilation of N may lead to species-specific responses to rising atmospheric CO₂. In addition to inorganic N sources, a substantial portion of plant N requirement can come from soluble organic N such as amino acids. Temperate forest trees are particularly suited to utilize organic N either by direct root uptake or by symbiotic association with mycorrhizal fungi. Here we report growth responses of seedlings of Acer rubrum and Fraxinus pensylvanium (arbuscular mycorrhiza), and Quercus rubra and Pinus taeda (ectomycorrhiza) to CO₂ enrichment (360 and 720 ppm), mycorrhizal inoculation (with or without) and N source (ammonium nitrate or glycine plus glutamine at identical 1mM N), in a factorial design. Elevated CO₂ increased total biomass the most in Quercus (130%) and the least in Fraxinus (116%). Although CO₂ response did not depend on N source, species varied in their ability to utilize either N source. Quercus and Pinus grew better (10% and 20%, respectively) with amino acids as an N source while Acer and Fraxinus tended to prefer ammonium nitrate. Over all, mycorrhizal inoculation reduced total biomass, but there was no significant CO₂ by mycorrhiza interaction. Mycorrhizal inoculation, however, altered fine root:total biomass ratio differently in AM vs. EM species: decreased in EM species, but increased in AM species. This study shows that these species differ in their ability to utilize amino acids as an N source, but such differences cannot be attributed to mycorrhizal status of the roots. Furthermore, growth responses to elevated CO₂ is similar for organic vs. inorganic N sources.

KEY WORDS: Elevated CO₂, Amino acids, Mycorrhizae, Trees