Nitrogen availability and maize genotype shape nitrification through shifts in soil microbial functional diversity

Background Emerging evidence indicates that maize genotypes regulate rhizosphere microbial processes through distinct interactions with microbiota, shaping soil organic matter mineralization (SOM) dynamics and N cycling pathways. Although both SOM mineralization and nitrification depend on genotype and N availability, the mechanistic link between genotype-driven carbon mineralization and nitrification remains poorly understood. Specifically, it remains unclear whether maize genotypes that stimulate greater SOM mineralization also promote higher net nitrification rates following N fertilization. We therefore investigated whether maize genotypes with a greater capacity to stimulate SOM mineralization exhibit higher net nitrification under contrasting N inputs. Results We categorized tropical maize ( Zea mays ) genotypes that previously showed variation in SOM mineralization as high (DTPYC9-F143-5–4-1–2), medium (CML421 = P31DMR#1–55-2–3-2–1), and low ([CML312/CML444//[DTP2WC4H255-1–2-2-BB/LATA-F2-138–1-3–1-B]-1–3-2–3-B]-2–1-2) SOM mineralizers, and applied N fertilizer at 50 and 100 kg N ha −1 , representing low and high N regimes, respectively. Soil functional diversity and microbial activity were assessed using MicroResp™ assays, while qPCR was used to quantify the abundance of the ammonia monooxygenase ( amoA ) genes in archaea (AOA) and bacteria (AOB), and changes in the size of the bacterial community (16S rRNA gene copies). Nitrogen addition enhanced soil microbial biomass carbon (MBC) by 15%, basal activity by 8%, and net nitrification by 521% in the absence of maize plants, whereas the maize genotypes under a high N regime increased the basal activity by 5 – 25% and net nitrification by 52- 370%, depending on genotype. The presence of maize and the N regime strongly exerted selective pressure on the microbial community. Nitrogen rate, rather than maize genotype, strongly influenced the abundance of AOA, AOB, and 16S rRNA genes. Across the maize genotypes, nitrification and microbial activity were inversely related to the genotype-specific order of SOM mineralization. The clustering of microbial community-level physiological profiles (MCLPPs) depended on plant presence and N regime. NUE of the maize genotypes increased with increasing SOM mineralization associated with these genotypes. Conclusion Collectively, our findings redefine the relationship between SOM mineralization and nitrification by showing that enhanced SOM mineralization is typically not associated with increased nitrification. Instead, we demonstrate that genotypic-specific regulation of microbial activity and N transformations depends on N input rates, underscoring that a maize genotype''s capacity to regulate nitrification is context-dependent. Thus, integrating genotype selection with optimized N management offers a promising strategy to enhance conservation and use efficiency, sustain biomass yield, and minimize N losses that harm the environment.