Eighty years of maize breeding alters plant nitrogen acquisition but not rhizosphere bacterial community composition

Aims There is considerable interest in breeding for crop genotypes that harness rhizosphere microbial communities and processes in support of plant productivity. However, the extent to which past breeding efforts have altered plant rhizosphere traits and plant-microbe collaborations is unknown. Methods We evaluated twelve best-selling and widely adapted maize hybrids released between 1936 and 2011 for changes in rhizosphere bacterial community composition (BCC) and plant access to endogenous soil nitrogen. Plants were grown in replicated monocultures fertilized with 0, 85 or 170 kg N ha−1 and measured for yield, nitrogen uptake and source. Rhizosphere BCC and function was assessed through potential extracellular enzyme assays and 16S rRNA gene amplicon sequencing. Results Grain yield and nitrogen uptake from soil pools increased with year of hybrid release at all fertilization levels. Rhizosphere BCC and enzyme activity also varied among hybrids. However, releases from the 1960s and 70s were most distinct, while early and late releases shared similar BCC and enzyme activity. Conclusions These results indicate that breeding has increased maize ability to acquire nitrogen from soil reserves, but has not resulted in a directional shift in rhizosphere bacterial community assembly. The variation observed among hybrids reveals the potential for future breeding efforts to influence rhizosphere traits.