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ARS Home » Midwest Area » Urbana, Illinois » Global Change and Photosynthesis Research » Research » Publications at this Location » Publication #314545
Title: Inoculation with an enhanced N2-fixing Bradyrhizobium japonicum strain (USDA110) does not alter soybean (Glycine max Merr.) response to elevated [CO2]

Author
item SANZ-SAEZ, A - University Of Illinois
item HEATH, K - University Of Illinois
item BURKE, P - University Of Illinois
item Ainsworth, Elizabeth - Lisa

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2015
Publication Date: 5/27/2015
Citation: Sanz-Saez, A., Heath, K.D., Burke, P.V., Ainsworth, E.A. 2015. Inoculation with an enhanced N2-fixing Bradyrhizobium japonicum strain (USDA110) does not alter soybean (Glycine max Merr.) response to elevated [CO2]. Plant Cell and Environment. DOI: 10.1111/pce.12577.

Interpretive Summary: Soybean and other legumes form symbiotic associations with nitrogen-fixing bacteria (rhizobia) in which the legume host forms and maintains a root nodule where it supplies reduced carbon to fuel bacterial nitrogen fixation. This symbiosis can consume up to 11% of recently fixed carbon, and in this study we examined if inoculation of soybean with an enhanced rhizobium strain would impact soybean response to rising atmospheric CO2 concentrations. We were able to manipulate nodule occupation in the field, but did not find evidence for a greater stimulation of growth or yield at elevated CO2. The results suggest that there is competition from less efficient rhizobia in field soils, which limits the benefit of the enhanced strain.

Technical Abstract: This study tested the hypothesis that inoculation of soybean (Glycine max Merr.) with a selected Bradyrhizobium japonicum strain (USDA110) with greater N2 fixation rates would enhance soybean photosynthetic, growth and yield response to elevated [CO2]. In field experiments at the Soybean Free Air CO2 Enrichment (SoyFACE) facility, inoculation of soybean with USDA110 successfully increased nodule occupancy to 54% in elevated [CO2] and 34% at ambient [CO2]. However, despite this success, inoculation with USDA110 did not result in greater photosynthesis, growth or seed yield at ambient or elevated [CO2] in the field, presumably due to competition from native rhizobia. Inoculation of soybean with USDA110 under controlled conditions with sterilized soil resulted in nodule occupation of >90%, significantly greater 15N2 fixation, and greater leaf N and total plant biomass accumulation compared to plants grown with native soil bacteria. However, there was no interaction of rhizobium fertilization with [CO2]; inoculation with USDA110 was equally beneficial at ambient and elevated [CO2]. These results suggest that high-quality selected rhizobia have the potential to stimulate soybean yield in soils with little or no history of prior soybean production, but that better-quality rhizobia do not necessarily enhance plant responses to elevated [CO2].