PGPR inoculation and chemical fertilization of cereal crops, how do the plants and their rhizosphere microbial communities’ response?

Abstract

Soil microorganisms have a preponderant role in most ecosystem processes, and different crop management strategies applied to agricultural production can modify microbial physiology and biodiversity. However, at field conditions, the effects of the application of chemical fertilizers and microbial bioinsumes on native microbial communities are not completely known. Results from several independent experiments performed for wheat and maize in different years at establishments of the province of Buenos Aires, Argentina, are discussed. Inoculants were formulated with Azospirillum brasilense, one of the most worldwide studied plant growth-promoting rhizobacteria. Multi-strain inoculants have greater advantages than mono-strain inoculants. Inoculation and chemical fertilization did not modify functional diversity, characterized through the community-level physiological profiles (CLPP), and they did not affect most of the evaluated rhizosphere microbial communities such as cellulose degraders, diazotrophs, and nitrifiers. Modifications in Shannon’s index of these communities determined from CLPP data were observed throughout the crop cycle and between different crops. Thus, 40M and 42M strains have shown great potential to be used as biofertilizers in both cereal crops. Inoculation and chemical fertilization, at least at the levels evaluated, constitute good agricultural practices for food production in a sustainable way. This knowledge provides tools not only to improve crop inoculation response with A. brasilense in interaction with chemical fertilization but also to characterize the ecological risk of both agronomic practices. This chapter shows scientific information allowing to connect processes which occur in the aerial portion of the system with those that take place underground. Academic, productive, and environmental implications are directly transferable to advisers and farmers, under the current paradigm of the bioeconomy and sustainable agriculture.