Unravelling the interplay of different traits and parameters related to nitrogen use efficiency in wheat for climate-resilient agriculture

Enhancing Nitrogen Use Efficiency (NUE) is extremely important towards mitigating climate change, especially in wheat where the NUE is less than 50%. Hence, optimizing grain yield under reduced application of nitrogenous fertilizer is a significant challenge. To address this challenge, a comprehensive study was conducted to investigate various agronomic traits and morphological, biochemical and molecular parameters related to NUE. This study explored their interrelationships and effects on grain yield, providing novel insights that were not previously reported. A set of 278 diverse wheat genotypes were assessed, encompassing eight NUE-related field traits. All traits' values were reduced under stressed N (ranging from 7.5% to 77.5%) except Nitrogen Utilization Efficiency (NUtE) and NUE. Data analysis showed a significant positive correlation between grain yield and all other NUE-related traits (r² value ranged from .23 to 1.00), highlighting their relevance in comprehending the biological NUE of wheat plants. Principal component analysis (PCA) also revealed that N at head and N at harvest were more connected with gain yield, NUE and biomass under the optimum N condition, but less connected with gain yield and NUE under the stressed N condition. To complement the field data, representative genotypes were further subjected to a hydroponics experiment under absolute N control to study the different morphological parameters, photosynthetic pigments and the performance of essential N- and C-metabolizing enzymes at the seedling stage. N stress had a detrimental impact on the majority of the parameters (−0.84% to −79.8%). Nitrite reductase (NiR), glutamate dehydrogenase (GDH) and isocitrate dehydrogenase (ICDH) enzymes as well as root length (RL), root fresh weight (RFW) and CS transcript, were positively affected by 5.9%–35.6%. The correlation analysis highlighted the substantial influence of four key N-metabolizing enzymes, namely nitrate reductase (NR), glutamine synthetase (GS), glutamate oxo-glutarate aminotransferase (GOGAT), and GDH on grain yield. Additionally, this study highlighted the direct and indirect associations between seedling parameters and field traits, where shoot and root length were found to be most significant for N acquisition, especially under N stress. In conclusion, these findings offer valuable insights into the intricate network of traits and parameters influencing wheat grain yield under varying N regimes.