Evaluation of nitrous oxide emission by soybean inoculated with Bradyrhizobium strains commonly used as inoculants in South America

Aims: The purpose of this work was to analyze the agronomic and environmental performance of soybean plants inoculated with the Bradyrhizobium strains widely used as soybean biofertilizers in South America and to determine if these strains possess any functional or taxonomic trait associated with the NO emission. Methods: Bradyrhizobium japonicum E109 and CPAC 15, B. diazoefficiens USDA 110 and CPAC 7, and B. elkanii SEMIA 5019 and SEMIA 587 were used to inoculate soybean seeds. The field experiment was carried out in a soil without history of soybean cultivation in the Argentinian Humid Pampa. The natural N abundance method was applied to estimate N-fixation, and NO production was evaluated using gas chromatography. Among other physiological parameters, shoot dry weight, shoot N content, and crop yield were estimated after harvest. Results: B. japonicum inoculation produced the greatest increases in soybean growth and crop yield but also led to higher NO emissions compared to all other inoculated treatments. Plants inoculated with B. diazoefficiens released the lowest amount of NO, and their growth and yield were the least affected. Inoculation with B. elkanii resulted in intermediate NO emission fluxes and crop yield compared with B. japonicum and B. diazoefficiens. Conclusions: We found that soybean inoculation with strains of B. japonicum and B. elkanii that lack the nosZ gene led to the highest NO emissions under field conditions, but also to the highest crop yield, while inoculation with strains that carry out complete denitrification, nosZ-containing B. diazoefficiens, showed lower NO emission and lower crop yield.To the Instituto de Investigaciones Agrobiotecnológicas (INIAB); Universidad Nacional de Río Cuarto (UNRC); Consejo Nacional de Investigaciones Científcas y Tecnológicas (CONICET), Fondo Nacional de Ciencia y Tecnología (FONCyT); Instituto Nacional de Tecnología Agropecuaria (INTA). FC is Researcher of CONICET at the UNRC. DT and FD are Postdoc and PhD students at the UNRC granted by CONICET. MOC is a former PhD student at the UNRC granted by CONICET. To Mariano Cicchino from INTA Chascomús, who was in charge of sowing and yield estimation at R8. To Juan Pedro Ezquiaga from INTA Castelar, for their contribution to N2O measurements

Azospirillum as Biofertilizer for Sustainable Agriculture: Azospirillum brasilense AZ39 as a Model of PGPR and Field Traceability

Azospirillum is one of the best studied genus of plant growth promoting rhizobacteria at present. These bacteria are able to colonize hundreds of plant species and significantly improve their growth, development and productivity under field conditions. Besides nitrogen fixation, the most studied mechanism proposed for Azospirillum to explain plant growth promotion of inoculated plants has been related to its ability to produce several phytohormones, mainly auxins and particularly indole-3-acetic acid. Although different capacities have been described to explain the plant growth regulation by Azospirillum one single mechanism is not quite extensive to explain the full effect observed on inoculated plants. The bacterial mode of action is currently better explained as the result of additive and selective effects. One of the most important achievements obtained thus far is the utilization of azospirilla as commercial inoculants in approximately 7.0 million doses and 5.0 million ha, mainly cultivated with cereal crops and legumes in South America. Different inoculation practices (farmer applied or industrial seed treatments, infurrow, foliar or soil sprayed applications) have been developed and improved in the last two decades for a wide range of crops, in field conditions. Particularly, the combined inoculation of legumes with rhizobia and azospirilla, could over improve the performance of the plants compared with a single inoculation, due to the complementary biological processes of both microbes. The development and validation of specific novel methodologies for identification of A. brasilense, and particularly the strain Az39 in both bio-products and inoculated samples (i.e. soil, rhizosphere, seeds or plant tissues) offer a precise tool to evaluate the functionality and traceabilityof these microorganisms in the environment. In this chapter, we explore some classical mechanisms of plant growth promotion in A. brasilense Az39, one of the most widely used PGPR strains for inoculant production in South America. Additionally, we discuss some novel molecular tools designated to identify this strain in both bio-products and field conditions.Instituto de Microbiología y Zoología Agrícola (IMYZA)Fil: Coniglio, Anahí. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Físico-Químicas y Naturales. Departamento de Ciencias Naturales. Laboratorio de Fisiología Vegetal y de la Interacción Planta-Microorganismo (LFVIPM); ArgentinaFil: Mora, Verónica. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Físico-Químicas y Naturales. Departamento de Ciencias Naturales. Laboratorio de Fisiología Vegetal y de la Interacción Planta-Microorganismo (LFVIPM); ArgentinaFil: Puente, Mariana Laura. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Microbiología y Zoología Agrícola (IMyZA); ArgentinaFil: Cassán, Fabricio. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Físico-Químicas y Naturales. Departamento de Ciencias Naturales. Laboratorio de Fisiología Vegetal y de la Interacción Planta-Microorganismo (LFVIPM); Argentin