Impact of elevated CO₂ on carbohydrate and ureide concentrations in soybean inoculated with different strains of Bradyrhizobium japonicum

Abstract

Elevated CO2 increases soybean growth and photosynthesis, and the resulting additional supply of photosynthates stimulates nodule activity. To characterize its biochemical response to both CO2 and bradyrhizobial strains, soybean inoculated with three strains of Bradyrhizobium japonicum was grown in growth chambers under ambient (400 µmol·mol–1) or elevated (800 µmol·mol–1) CO2. Soluble sugars were generally more abundant in leaves and nodules under elevated CO2, while starch and pinitol were depleted, indicating that additional photosynthates were rapidly used, in particular for nodule growth (dry mass increased by 65%). Ureides (allantoin and allantoic acid) increased under elevated CO2 in leaves, while this increase was not significant in nodules. The indigenous strain 12NS14 induced the highest ureides concentration in nodules under elevated CO2 along with the highest nitrogenase activity and increase in shoot dry mass, indicating a positive-feedback stimulation: soybean mobilized energy reserves to support more nodules, and in return nodules synthesized more ureides to support plant growth. In contrast, the commercial strain 532c resulted in the highest ureide concentrations in leaves, coupled with the lowest nitrogenase activity and nodules yield, suggesting a feedback inhibition of nodule activity. Our results show that selection of B. japonicum strains better adapted to elevated CO2 could improve soybean performance.

Current Advances in Plant Growth Promoting Bacteria Alleviating Salt Stress for Sustainable Agriculture

“…Symbiotic associations of plants with soil microbes such as nitrogen-fixing bacteria (Frankia and Rhizobia) and mycorrhizal fungi may have a positive impact on plant salt stress tolerance [173]. Additionally, stress-tolerant rhizobial strains may help legume plants to preserve the level of N fixation and plant productivity [174]. Salinity tolerant Rhizobium bacteria are more efficient in promoting plant growth under saline conditions [175].…”

Asparagine: an amide of particular distinction in the regulation of symbiotic nitrogen fixation of legumes

“…Additionally, the implication of ASN as a Mn-chelating agent can probably result in a lower activity of NAD-malic enzyme in nodules (Todd et al, 2006). The NAD-malic is an essential enzyme that plays a critical role in providing energy and C for the N 2 ase activity as well as assimilation of the fixed-N. Exogenous Mn-application under water deprivation conditions has been shown to increase the apparent ureide-catabolic rate in the leaves and to have stimulatory effects on N 2 fixation in soybean (Vadez et al, 2000b;King & Purcell, 2005), while supplemental ASN has increased the nodule ASN/ureide ratio, resulting in a strong inhibition (90%) on acetylene reduction activity (ARA) (King & Purcell, 2005;Bertrand et al, 2011). Overall, the provided data are consistent with the hypothesis that ASN might be the potential messenger which inhibits ureide-degradation in shoots and conveys the critical information for controlling the N 2 ase activity in soybean symbiotic tissue (Serraj et al, 2001;Purcell, 2009).…”

Inoculation with an enhanced N2‐fixing Bradyrhizobium japonicum strain (USDA110) does not alter soybean (Glycine max Merr.) response to elevated [CO2]

“…This and other studies have led to the hypothesis that legume productivity responses to elevated [CO 2 ] could be improved by selecting strains that fix more N 2 and thus consume more C (Bertrand et al . , ; Prévost et al . ; Sanz‐Sáez et al .…”