Title : A novel plant–nifH gene microbial alliance in aerial roots of Mexican maize landraces significantly reduces nitrogen fertilizer requirements.
Abstract:
Modern and globally grown Zea Mays L. (maize) cultivars require large amounts of nitrogen (N) fertilizer that is costly for farmers, has high energy requirements, and can have detrimental environmental impacts. A novel solution was recently identified in maize landraces from Oaxaca, Mexico. These accensions excrete mucilage in aerial roots, providing ideal habitat for bacteria that fix significant amounts of atmospheric N2. However, little information is available on Biological Nitrogen Fixation (BNF) rates and microbial community composition on aerial roots of these landrace and modern maize accessions. Therefore, the objective was to determine the impact of these cultivars on the diversity of the total bacterial community and the diazotrophic bacterial communities; and BNF of the mucilage of aerial roots. The second objective was to compare rhizosphere soil with mucilage for diversity of total and diazotrophic bacterial communities. The field experiment at Columbus/Ohio, USA was a completely randomized block design that had seven treatments (four replications) that included wild type, Mexican landrace, and modern maize accessions. Bulk soil and rhizosphere soil were collected in June 2024 at the maize V6 growth stage, with mucilage and aerial root collection occurring from August 2 to September 15, 2024. Bacterial community and diazotrophic bacterial diversity in soil and mucilage were determined by high-throughput sequencing of 16SrRNA and cs respectively; and BNF measured in mucilage using a 15N2 incubation method. nifH sequencing showed that microbial diversity and amplicon sequence variants (ASVs) were significantly higher in mucilage of heirloom and improved accessions compared to wild and landrace maize types. Furthermore, the community structure of nifH-harboring bacteria significantly differed among various maize accessions, with pantoea being closely associated with N and BNF in mucilage, while skermanella was solely related to BNF. The microbial diversity of nifH-harboring bacteria was generally higher in rhizosphere soil – with Mexican landrace maize from the lowlands showing the highest diversity – compared to mucilage and bulk soil. The similarities and differences of N2-fixing bacterial communities in maize mucilage and soil are apparent but the mechanisms related to the genetic diversity of maize varieties in controlling mucilage habit to optimize N2 fixation need further investigation.
