Elucidating the evolutionary context of nitrification suppression in model Poaceae

Background/Question/Methods

A novel plant phenotype has recently been discovered in grasses called biological nitrification inhibition (BNI), whereby roots release chemicals that inhibit ammonium oxidizing (nitrification) bacteria, increasing plant-available ammonium. BNI is an attractive solution for crop development and breeding because it reduces nitrogen loss by preventing nitrate leaching and nitrous oxide emission. Therefore, the BNI trait is currently under intense investigation due to the potential benefits to nutrient management and ecosystem health. However, the evolutionary history of BNI is unknown, leaving gaps in our understanding of the origin of this beneficial phenotype. It is hypothesized that modern grasses, like maize (Zea mays), have been artificially selected within nutrient-rich environments (due to fertilization), selecting against the maintenance of BNI in the genomes of modern varieties. Previous research implies that wild and landrace maize varieties have greater BNI capacity than modern inbred varieties. Unfortunately, quantitative trait analyses required for studying the genomic source of the BNI phenotype are in their infancy and cannot confirm this hypothesis with genomic data yet. Therefore, this study aims to identify the fitness benefits of nitrification suppression, a proxy for BNI, in model Poaceae sorghum (Sorghum bicolor) and Brachypodium distachyon.

Results/Conclusions

Genotypic variation in rhizosphere nitrification potential was observed in Sorghum bicolor and Brachypodium distachyon. In agreement with previous maize research, breeding history (R2c = 0.19, P < 0.001) and genotype (R2c = 0.38, P < 0.001) significantly influenced S. bicolor rhizosphere nitrification potential, suggesting breeding may influence the maintenance of nitrification suppression in S. bicolor genomes. Fitness benefits of genotypic variation in Brachypodium, across 40 genotypes, are being assessed to quantify selective mechanisms driving the presence of nitrification suppression in germplasm.