Soybean Inoculated With One Bradyrhizobium Strain Isolated at Elevated [CO2] Show an Impaired C and N Metabolism When Grown at Ambient [CO2]

Soybean (Glycine max L.) future response to elevated [CO] has been shown to differ when inoculated with B. japonicum strains isolated at ambient or elevated [CO]. Plants, inoculated with three Bradyrhizobium strains isolated at different [CO], were grown in chambers at current and elevated [CO] (400 vs. 700 ppm). Together with nodule and leaf metabolomic profile, characterization of nodule N-fixation and exchange between organs were tested through N-labeling analysis. Soybeans inoculated with SFJ14-36 strain (isolated at elevated [CO]) showed a strong metabolic imbalance, at nodule and leaf levels when grown at ambient [CO], probably due to an insufficient supply of N by nodules, as shown by N-labeling. In nodules, due to shortage of photoassimilate, C may be diverted to aspartic acid instead of malate in order to improve the efficiency of the C source sustaining N-fixation. In leaves, photorespiration and respiration were boosted at ambient [CO] in plants inoculated with this strain. Additionally, free phytol, antioxidants, and fatty acid content could be indicate induced senescence due to oxidative stress and lack of nitrogen. Therefore, plants inoculated with Bradyrhizobium strain isolated at elevated [CO] may have lost their capacity to form effective symbiosis at ambient [CO] and that was translated at whole plant level through metabolic impairment.This work was financially supported by the following grants: GRUPO Gobierno Vasco IT1022-16 and projects 32-2016-00043, 37-2017-00047, and 000049-IDA2019-38 from the Economic Development and Infrastructures Department of the Basque Country, Spain. DS was a recipient of a Ph.D. grant supported by the Public University of Navarra. AS-S was partially supported by a postdoctoral fellowship granted by the Education, and Linguistic Policy Department of the Basque Country, Spain and the Alabama Agricultural Experiment Station and the Hatch Program of the National Institute of Food and Agriculture, United States Department of Agriculture. Technical support by Azucena González, Phytotron Service, SGIker (UPV/EHU) is gratefully acknowledged