Changes in environmental CO2 concentration can modify Rhizobium-soybean specificity and condition plant fitness and productivity

Abstract

Over the past 10 years, it has been demonstrated in the literature that legume responses to elevated [CO2], whether positive, negative, or null, are in part dependent on the Rhizobium species and genotypes that establish symbiosis with the plant. However, all the strains used in these past experiments were isolated in field conditions at ambient [CO2]. We studied for first time the fitness response of soybean inoculated with a Rhizobium strain that has been previously isolated from nodules of plants grown at elevated [CO2] in field conditions at a FACE site. In experiments developed in controlled growth chambers, and in the field under ambient [CO2], the plants inoculated with the strain isolated at elevated [CO2] showed similar response as plants without inoculation. We hypothesize that deficient nodulation may be associated with a change in root exudates caused by the change in [CO2]. This study showed that the strains isolated in nodules at elevated [CO2] are not capable of properly nodulating soybean plants grown at ambient [CO2] and that the origin of strains do not ensure the performance of plants under the same conditions. However, more research is needed in order to understand how changes in environmental conditions can affect the symbiotic relationship and ultimately how we can improve plant fitness in a changeable world.