The impact of plant genotype, starter fertilization and a seed-applied biostimulant on native root-associated mycorrhizal and bacterial communities in maize

The sustainable intensification of maize cropping systems, applying a variety of tools available in crop genetics, fertilization and microbial inoculation, may reduce agricultural environmental impact. However, little is known about the effects of such techniques on the native root-associated microbiota, which is pivotal for preserving soil fertility and health. In this study, we investigated whether maize hybrids differing in their early vigor, nitrogen (N) and phosphorus (P) starter fertilization and a seed-applied biostimulant (containing Bacillus amyloliquefaciens IT-45) shape the communities of native rhizosphere bacteria and root-colonizing arbuscular mycorrhizal fungi (AMF). A factorial growth chamber experiment was set up with two maize genotypes in natural soil. Mycorrhizal colonization was evaluated with root staining. The diversity and composition of rhizosphere bacterial and root-colonizing AMF communities were assessed by PCR-DGGE of the 16S and 18S rDNA, respectively, and subsequent amplicon sequencing. Cluster analysis showed that the biostimulant treatment affected the rhizosphere bacterial communities of the ordinary hybrid more than that of the high early vigor hybrid. Moreover, the biostimulant treatment was associated with the recruitment of potentially beneficial bacteria in the rhizosphere of emerging plantlets of the ordinary maize. However, based on our data, maize genotype was the major driver of rhizosphere microbiota assembly. Regarding the mycorrhizal symbionts, starter fertilization resulted in a reduction of root colonization by AMF. Although the biostimulant alone had moderate effects on AMF colonization and AMF community diversity, the combined treatment with biostimulant and starter fertilization induced a consistent decline in both colonization and biodiversity indices. In addition, the effect of the two factors were modulated by maize genotype. Our results may contribute to the understanding of how specific cropping practices may impact root-associated microbial communities and to the successful implementation of innovative tools in sustainable and resilient agroecosystems.