Monitoring dynamics in ear-leaf physiology during maize grain filling: genotype and nitrogen impact on source–sink relations and yield

During maize grain filling, effective coordination between a high source capacity and a robust sink significantly enhances yield. These source–sink relationships are primarily influenced by genotype and nitrogen availability, and achieving a balance between them has been a challenge in modern maize hybrids. In this study, three maize hybrids (B73 × Mo17, B73 × Sids7, and B73 × NC358), sharing B73 as the female parent, were produced, field-grown, and maintained till maturity under limited and sufficient soil nitrogen. The impact of the developing reproductive sink on growth, yield, and dynamic changes in ear-leaf physiology was monitored at 0, 5, 10, 15, and 20 days after pollination. Under limited and adequate N conditions, B73 × NC358 outperformed B73 × Mo17 and B73 × Sids7 in yield and most tested traits. The enhanced yield in B73 × NC358 was associated with increased sink-strength traits and improved source capacity-related morpho- physiological characteristics. As grain filling progressed, B73 × NC358 consistently demonstrated higher biomass accumulation, leaf nitrogen, stover nitrogen, chlorophyll content, total soluble proteins, and elevated activities of nitrate reductase (NR) and glutamine synthetase (GS) compared to the other hybrids. Nitrogen limitation curtails grain yield, growth, and leaf metabolites; however, it induces starch accumulation and increased protease and asparaginase (ASNase) activities in all hybrids. Our findings suggest that B73 × NC358 optimizes leaf nitrogen and balances source capacity and sink strength to enhance biomass, nitrogen use efficiency (NUE), and grain yield. The alleles from B73 and NC358 interact effectively to support a stay-green-like phenotype, promoting growth and grain yield across nitrogen conditions.