Uncovering how Wheat Cultivars Combat Nitrogen Deficiency Differently

Nitrogen (N) fertilisers are essential for modern wheat production, yet less than half of the applied N is actually used by crops. The rest either accumulates in soil or escapes into the environment, contributing to pollution and waste.  

When plants face nutrient deficiency, some are able to actively ‘recruit’ beneficial microorganisms by altering their root exudates (organic compounds secreted by plant roots into surrounding soil). This “cry-for-help” strategy allows stressed plants to enlist microbial allies that help access nutrients, stimulate root growth, and improve stress tolerance.  

These mutualistic association between plants and microorganisms enhance the ability for plants to acquire and use N, especially important in nutrient-poor environments as these microorganisms in the rhizosphere (the soil zone directly influenced by plant roots) play a crucial role in transforming N into plant-available forms.  

It is known that some wheat cultivars (varieties bred for specific traits) use nitrogen more efficiently than others, though the processes responsible are largely unknown. To uncover the potential underlying mechanisms, a recent study from our Hub by Chan et al. (2026) reveals how wheat cultivars with contrasting nitrogen use efficiency (NUE) modulate their rhizosphere bacterial communities differently under N scarce and abundant environments. Through a controlled glasshouse experiment, our researchers focused on two Australian wheat cultivars: Mace (higher reported NUE) and Gladius (lower reported NUE).  The team sheds light on DNRA (Dissimilatory Nitrate Reduction to Ammonium) – a microbial process that converts N from a plant-unavailable to plant-available form – as a key mechanism supporting wheat growth under N stress. 

 

Key Finding: The DNRA Advantage 

Both cultivars showed clear signs of nitrogen deficiency under the nitrogen deficient (-N) treatment with aboveground biomass and total N content decreasing in both cultivars. However, their rhizosphere bacterial communities responded quite differently. 

Mace significantly increased the abundance of genes (nrfA, nrfD, and nrfH) which are involved in DNRA under N deficient conditions, while Gladius showed no such response. 

This matters as it shows that the Mace cultivar encourages DNRA, which releases ammonium into the soil, making N readily available for plant uptake. This contrasts with another pathway called ANRA (Assimilatory Nitrate Reduction to Ammonium), where N becomes locked up in microbes and thus unavailable to plants. 

Notably, while DNRA genes increased in Mace, ANRA genes (nasE and nasC) decreased, suggesting a strategic shift toward N-releasing rather than N-immobilising processes.  

 

Key Finding: Changes in Bacterial Composition 

The bacterial community composition in Mace’s rhizosphere underwent a significant shift under the -N treatment. Several bacterial orders became more abundant, notably Rhodocyclales, Nitrosomonadales, Hydrogenphilales, and Bdellovibrionales. 

Correlation analysis revealed that six bacterial orders, including Rhodocyclales, showed significant negative correlations with plant total N content. This means as plant N decreased, the abundance of these bacterial orders increased.  

Genes involved with DNRA were detected within the Betaproteobacteria class, to which Rhodocyclales belongs. Importantly, the abundance of nrfA and nrfH genes was significantly negatively correlated with plant total N content, suggesting that Mace stimulates DNRA bacteria when N becomes scarce. 

 

Why This Matters 

These findings reveal that wheat cultivars with contrasting reported nitrogen use efficiency interact differently with their rhizosphere bacteria. Specifically, the study identified significant differences in bacterial N metabolism gene composition between Mace and Gladius. 

The research provides important evidence that the rhizosphere bacterial DNRA pathway response to nitrogen deficiency differs between wheat cultivars. Under nitrogen deficiency, Mace demonstrated a higher capacity for DNRA, consistent with its reported NUE, while no significant changes were found in Gladius. This suggests that cultivar selection may be a relevant factor when developing strategies for sustainable agricultural practices, though further research is needed to understand these mechanisms and their practical applications. 

 

Read the full paper here: https://www.sciencedirect.com/science/article/pii/S2667006225000474?via%3Dihub