Unraveling the morphophysiological, biochemical, and yield responses of maize genotypes to contrasting nitrogen conditions using multivariate approaches

Genotypic variation plays a pivotal role in modulating the activity of nitrogen (N) assimilating enzymes, photosynthetic rate, N accumulation, plant growth, and yield. Despite this, the extent to which growth and N-assimilating enzymes exhibit differential responses across genotypes and their influence on yield and nitrogen use efficiency (NUE) remains inadequately explored. This study aimed to elucidate genetic variations among two inbred maize lines (Huang C and 178) and their hybrid (Huang C × 178) for key morphophysiological and biochemical traits under contrasting N conditions. Multivariate statistical methods, including principal component analysis (PCA) and structural equation modeling (SEM), were used to analyze and identify significant genotypic differences across most traits. The primary contributors to genetic variation were identified as N-assimilating enzymes, photosynthetic rate, N accumulation, and ear traits. Complete N deficiency significantly reduced root development, photosynthetic rate, and N-assimilating enzyme activities. Correlation analysis revealed strong positive relationships among N-assimilating enzyme activities, shoot N accumulation, and grain N accumulation, indicating that enhanced biomass production promoted higher grain yield. Moreover, strong positive correlations between N-assimilating enzymes and grain yield demonstrate the critical role of these enzymes in optimizing yield and NUE. Nitrogen use efficiency indices showed significant differences among genotypes, particularly in NUE, nitrogen recovery efficiency (NRE), nitrogen partial factor productivity (NPFP), nitrogen dry matter productivity (NDMP), and nitrogen harvest index (NHI). The highest heterosis was observed in N metabolism enzymes, photosynthetic rate, N accumulation, and yield components, indicating these traits as key improvement drivers. The study concluded that genetic variation in critical traits, such as N-assimilating enzyme activity, photosynthetic rate, N accumulation, and yield components, confers a significant advantage to the hybrid. These findings have practical implications for maize breeding programs, as they highlight the potential for improving NUE and yield through genetic selection. This could contribute significantly to sustainable agriculture by optimizing N input and minimizing environmental impact.