Abstracts - Posters

Effects of Elevated Atmospheric CO² on Nitrogen Fixation and Cold Acclimation in Alfalfa

Annick Bertrand¹, Francine J. Bigras, Danielle Prévost and Roger Lalande
¹Agriculture and Agri-Food Canadabr> bertranda@agr.gc.ca

The predicted rise in concentration of atmospheric CO² could affect a variety of plant processes, including photosynthesis, reserve accumulation and, ultimately, tolerance to environmental stresses. Perennial alfalfa (Medicago sativa L.) is a sustainable crop with a deep root system, living in symbiosis with rhizobia for nitrogen (N) fixation and, as such, is a good candidate for carbon (C) sequestration in agriculture. The objectives of the project were to determine the effects of elevated CO² on growth, N fixation, photosynthesis, accumulation of reserves and cold acclimation in alfalfa, and on the soil microflora. Plants inoculated with two rhizobial strains were grown two months at 20°C and then cold acclimated at 2°C under either 400 (ambient) or 800 (elevated) ppm of CO². Photosynthesis increased under elevated CO² and was higher in plants inoculated with rhizobial strain A2 than with strain NRG34. Growth of alfalfa was increased under elevated CO² with a higher root weight for alfalfa inoculated with strain A2 as compared to NRG34. Nitrogenase activity was also stimulated under elevated CO². Plants acclimated under ambient CO² were shown to be more freezing tolerant. Cryoprotective sugars linked with freezing tolerance increased in taproots during cold acclimation but did not differ between the two CO² treatments. Our results show that it is possible to identify rhizobial strains to improve plant performance under elevated CO². For instance, key genes of alfalfa metabolism were differentially expressed according to the symbiotic rhizobial strain. The study of the synergistic plant response to both atmospheric CO² and rhizobial strain is a promising emerging research avenue.

2005-04-06