Elevated CO2 induces differences in nodulation of soybean depending on bradyrhizobial strain and method of inoculation

Abstract

High CO 2 has been shown to increase plant growth and to affect symbiotic activity in many legumes species, including soybean (Glycine max [L.] Merr.). In order to assess the interaction between elevated CO 2 and rhizobial symbionts on soybean growth and nodulation, we combined the effects of CO 2 with those of different bradyrhizobial strains and methods of inoculation. Soybean seeds were sown in agricultural soil in pots and inoculated with three strains of Bradyrhizobium japonicum (5Sc2 and 12NS14 indigenous to Quebec soils, and 532c, a reference strain), the inoculum being either applied directly to the seed or incorporated into the soil. Plants were grown in growth chambers (22/17ºC) for 6 weeks, under either near ambient (400 μmol mol −1 ) or elevated (800 μmol mol −1 ) concentrations of CO 2. Elevated CO 2 increased mass (63%) and number (50%) of soybean nodules, particularly medium and large, allowed a deeper nodule development, and increased shoot dry weight (+30%), shoot C uptake (+33%) and shoot N uptake (+78%), compared to ambient CO 2 . The two indigenous strains induced more medium and large nodules under elevated CO 2 than the reference strain and showed the greatest increases in shoot dry weight. Soil inoculation induced higher number of small nodules than seed inoculation, specifically for the two indigenous strains, but did not affect plant growth parameters. We conclude that soybean yield enhancements due to elevated CO 2 are associated with the production of large and mediumsize nodules and a deep nodulation, that the two indigenous strains better respond to elevated CO 2 than the reference strain, and that the method of inoculation has little influence on this response.

Shifts in microbial communities in soil, rhizosphere and roots of two major crop systems under elevated CO2 and O3

“…2) showed that 96 out of 143 OTUs significantly enriched in the endosphere under eCO 2 conditions belonged to N 2 fixing bacteria, including unclassified members of Rhizobiales and Burkholderiaceae. This finding also corresponds to previous results showing that eCO 2 stimulated increases in both the mass and number of soybean nodules, along with a 33% increase in shoot C and a 78% increase in N uptake 57 .…”

Effect of elevated carbon dioxide on growth and nitrogen fixation of two soybean cultivars in northern China

“…Others also reported that the C/N ratio of soybean straw at maturity was unaffected by elevated [CO 2 ] Torbert et al 2004), although higher C/N ratio in fully expanded leaf was observed under elevated [CO 2 ] at vegetative and reproductive stages of soybean (Ainsworth et al 2007). The increases in C accumulation (17%; p<0.05) and N uptake (21%; p<0.05) of the above-ground parts of soybean under CO 2 enrichment (Table 1) are consistent with Prévost et al (2010).…”

Influence of Elevated Atmospheric Carbon Dioxide on Transcriptional Responses of <i>Bradyrhizobium japonicum</i> in the Soybean Rhizoplane

“…Although alteration of the carbon supply due to enhanced CO 2 fixation rates has been postulated to directly influence nitrogen cycling in soils ( 21 ), the influence of this greenhouse gas on the nitrogen-fixing symbiosis between B. japonicum and soybean is poorly understood. Recently, however, Prévost et al ( 38 ) reported that elevated atmospheric CO 2 increased soybean nodule number and mass, and increased shoot dry weight, and C and N uptake compared to ambient CO 2 . The reasons, however, for the reported CO 2 -induced enhancement of the symbiosis are currently unknown.…”

“…The biomass of several legumes species, including Acacia species, alfalfa ( Medicago sativa ), and mungbean ( Vigna radiata ), have been shown to increase under conditions of elevated CO 2 , and increased plant growth has sometime been correlated with enhanced nodulation and nitrogenase activity ( 7 , 50 ). Elevated atmospheric CO 2 has also been shown to increase nitrogen fixation activity and nodulation of Bradyrhizobium in symbiosis with soybean ( Glycine max ) ( 38 ) and dry matter production by 50% ( 2 ).…”