Submitted to: International Scholarly Research Network (ISRN)
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/29/2012
Publication Date: 3/1/2012
Citation: Abi-Ghanem, R., Carpenter-Boggs, L., Smith, J.L., Vandemark, G.J. 2012. Nitrogen fixation by U.S. and Middle Eastern chickpeas with commercial and wild Middle Eastern inocula. International Scholarly Research Network (ISRN). Volume 2012, Article ID 981842, 5 pages. Interpretive Summary: Over 12 million tons of fertilizer nitrogen is applied annually in North America. By 2005, synthetic nitrogen provided three times as much nitrogen to agriculture as biological nitrogen fixation on a global basis. Biological nitrogen fixation presents economic, environmental, and agronomic benefits and could be used to a larger degree as an alternative to synthetic fertilizers. One strategy for enhancing crop nitrogen fixation is developing varieties that have higher rhizobium infection rates. We found that plant fixed nitrogen was significantly influenced by different inoculant strains, and by the variety of chickpea. Among varieties, Sierra, Troy and Almaz had the highest PNF of 86.7%, 85.3%, and 85.2%, respectively. These findings suggest that N fixation improvement in lentils and peas may be addressed most effectively by breeding crops for greater N fixation hosting capacity. This research clearly shows that simply breeding legumes for yield potential may be a flawed strategy for the best environmental use of nitrogen. This study will help convince breeders to breed plants for increased N fixation, in turn this will decrease N fertilizer use that effects climate change, environmental quality and human health.
Technical Abstract: Chickpeas (Cicer arietinum L.) are native to the Middle East (ME), and must be inoculated with symbiotic bacteria in order to fix nitrogen (N) in North American soils. Commercial inocula for chickpea contain several strains of the known N-fixing symbiont Mesorhizobium ciceri. It is not known whether the available M. ciceri strains are more or less effective than other wild strains from ME soils when paired with various chickpea variety hosts. This study was conducted to isolate N fixing bacteria symbiotic with chickpea from ME soils and to compare their effectiveness against commercial strains on U.S. and ME varieties of chickpeas. Chickpeas were inoculated with individual strains and grown in growth chambers for 8 weeks. Plants received 2 mM (15NH4)2 SO4 (5% atom excess) to allow measurement of N fixation by isotope dilution. The PNF was significantly influenced by different inoculant strains, and by the variety of chickpea. Among varieties, Sierra, Troy and Almaz had the highest PNF of 86.7%, 85.3%, and 85.2%, respectively. Among strains, Jord-M1 contributed to greater PNF (84.7%) compared to Syr-M1 (81.4%). Overall, chickpea varieties had a greater effect on PNF than did strain selection. This finding supports efforts to increase agricultural N fixation that focus on varietal breeding and selection. Wild ME symbionts belonged to the genus Burkholderia, and this discovery warrants the study of N-fixing bacteria beyond the currently known symbionts.