Nitrogen Fertilizer Type and Genotype as Drivers of P Acquisition and Rhizosphere Microbiota Assembly in Juvenile Maize Plants

Phosphorus (P) is an essential nutrient for plant growth and development, as well as an important factor limiting sustainable maize production. Targeted nitrogen (N) fertilization in the form of ammonium has been shown to positively affect Pi uptake under P-deficient conditions compared to nitrate. Nevertheless, its profound effects on root traits, P uptake, and soil microbial composition are still largely unknown. In this study, two maize genotypes F160 and F7 with different P sensitivity were used to investigate phosphorus-related root traits such as root hair length, root diameter, AMF association, and multiple P efficiencies under P limitation when fertilized either with ammonium or nitrate. Ammonium application improved phosphorous acquisition efficiency in the F7 genotype but not in F160, suggesting that the genotype plays an important role in how a particular N form affects P uptake in maize. Additionally, metabarcoding data showed that young maize roots were able to promote distinct microbial taxa, such as arbuscular mycorrhizal fungi, when fertilized with ammonium. Overall, the results suggest that the form of chemical nitrogen fertilizer can be instrumental in selecting beneficial microbial communities associated with phosphorus uptake and maize plant fitness.