Isotopic fractionation during N2 fixation by chickpea

Abstract

Abstract Desi and Kabuli chickpea (Cicer arietinum L) inoculated with Mesorhizobium ciceri strain CP39 or a mixture of strains 27A2, 27A7 and 27A9 were grown in N-free nutrient solution in a growth chamber. At the flowering stage shoot N was significantly higher for the Kabuli plants inoculated with strain CP39 than those inoculated with the multi-strain but did not differ between the inoculant strains in the Desi chickpea. For both chickpea types, seed N concentrations were not different between the inoculant strains. The total N of the shoots at flowering and seed harvested at physiological maturity for each host-Mesorhizobium combination was depleted in 15N relative to the atmospheric N2 (0‰). The 15N natural abundance (δ15N) in the shoots at flowering, ranged from −1.3067 to −2.8225‰, and those for the seed ranged from −0.5475 to −0.9062‰. Consequently, measures of isotopic fractionation (β) during N2 fixation ranged from 1.0013 to 1.0028 for the shoots at flowering and 1.0005–1.0009 for the seed harvested at physiological maturity. The isotopic effect was not influenced by the infecting rhizobial strain at the flowering stage in the Desi chickpea, but the effect was dependent on the rhizobial strain in the Kabuli chickpea. In contrast, whereas the β values for the harvested Desi seed differed between strain CP39 and the mixed strains (27A2, 27A7 and 27A9), those for the harvested Kabuli seed were not different.