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

• Published in: Plant, cell and environment Vol. 38; no. 12; pp. 2589 - 2602
• Main Authors: Sanz‐sáez, Álvaro, Heath, Katy D, Burke, Patricia V, Ainsworth, Elizabeth A
• Format: Journal Article
• Language: English
• Published: United States Blackwell Scientific Publications 01.12.2015; Wiley Subscription Services, Inc
• Subjects: air; Biomass; Bradyrhizobium - physiology; Bradyrhizobium japonicum; carbon dioxide; Carbon Dioxide - pharmacology; elevated carbon dioxide; field experimentation; free air carbon dioxide enrichment; free air CO2 enrichment; Glycine max; Glycine max - drug effects; Glycine max - microbiology; Glycine max - physiology; growth chambers; leaves; N2 fixation; nitrogen; nitrogen content; Nitrogen Fixation; nodulation; photosynthesis; Photosynthesis - physiology; rhizobia; seed yield; soil; soil bacteria; Soil Microbiology; soil sterilization; soybeans; stable isotopes; Symbiosis; N2 fixation; nodulation; elevated carbon dioxide; rhizobia; free air CO2 enrichment
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.12577

This study tested the hypothesis that inoculation of soybean (Glycine max Merr.) with a Bradyrhizobium japonicum strain (USDA110) with greater N₂ fixation rates would enhance soybean response to elevated [CO₂]. In field experiments at the Soybean Free Air CO₂ Enrichment facility, inoculation of soybean with USDA110 increased nodule occupancy from 5% in native soil to 54% in elevated [CO₂] and 34% at ambient [CO₂]. 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. In a growth chamber experiment designed to study the effects of inoculation in the absence of competition, inoculation with USDA110 in sterilized soil resulted in nodule occupation of >90%, significantly greater ¹⁵N₂ fixation, photosynthetic capacity, leaf N and total plant biomass compared with plants grown with native soil bacteria. However, there was no interaction of rhizobium fertilization with elevated [CO₂]; inoculation with USDA110 was equally beneficial at ambient and elevated [CO₂]. These results suggest that selected rhizobia could potentially stimulate soybean yield in soils with little or no history of prior soybean production, but that better quality rhizobia do not enhance soybean responses to elevated [CO₂].