Emission of greenhouse gases and Bradyrhizobium‐soybean interaction

OBLANDO CASTELLANO, MELISSA; DONADÍO, FLORENCIA; BEDMAR, EULOGIO; CASSÁN, FABRICIO

Congreso; XXXIV Reunión Científica Anual de la Sociedad de Biología de Cuyo; 2016

The progressive ascent of greenhouse effect gases in the atmosphere is contributing significantly to global warming. Agriculture is a major sources emissions of these gases, especially nitrous oxide (N2O), which is mostly is produced. The application of nitrogen fertilizers in agricultural soils increases the emission of these gases since they mainly originate in the nitrogen cycle. Argentina and Brasil are second and third largest soybean producer in the world with an 2015 season crop yield of about 60 million tons. The inoculation of this legume with Bradyrhizobium genus is a common practice in South America, and some regions have used this practice for more than 40 years. However, only a small percentage of isolated Bradyrhizobium strains from Argentinian soils are true denitryfing. Due to the fact that N2O emissions in soybean nodules have been proved, and if we consider large extensions de cropped soils with that legume, soybean could become a main source of emission of greenhouse effect gasses to the atmosphere. Since denitrifying activity of these strains is still unknown, the main aim of this study is to test NO and N2O emissions from Bradyrhizobium strains currently used as soybean biofertilizers in order to make it possible to formulate future environment-friendly inoculants. The information on the emission inventory derived from the legume-rhizobium interaction is incipient and available reports confirm that important N2O values occur in this symbiotic process. Recent studies indicate that the production of N2O in both the symbiotic interaction and in soils cultivated with legumes shows a higher production of this gas compared to soils cultivated with non-legume species. In the case our country, denitrifying activity from the most used strains for legume inoculation in Brasil [SEMIA 5019 y 5080 strains (B. diazoefficiens); SEMIA 5019 y 587 strains (B. elkanii)] and Argentina [E109 strain (B. japonicum)] was analyzed. These strains present incomplete denitrification and therefore, they are emitters of nitrous oxide in free living. In addition, N2O production was determined in symbiosis with soybean roots. The emission of this gas presents significant differences when these strains were inoculated in comparison with the low emission from USDA110 and SEMIA 5080 strains (denitrification complete rhizobia). As an alternative to N2O mitigation, it was found that the possible mixed inoculations between rhizobia with complete and incomplete denitrification decrease the N2O production in nodulated soybean roots, with the combinations between E109, SEMIA 5019 and the complete denitrification strains being the most effective to reduce the emission of this gas. According to this, it is necessary to continue with future investigations that allow knowing potentially effective alternatives that contribute with the mitigation of the emission of nitrous oxide product of the interaction Bradyrhizobium - Soybean.