The central role of ear nitrogen uptake in maize endosperm cell and kernel weight determination during the lag period

Abstract

Although kernel weight (KW) has proven to be an increasingly important driver behind grain yield (GY) variability in modern maize hybrids, nitrogen’s (N) role in the determination of individual sink capacity (i.e., potential KW) during the lag phase of reproductive development remains unclear. The research objective was to study the relationships between endosperm cell number (ECN) during the lag phase (an indicator of potential KW) and final KW within the context of changing plant N dynamics in field-grown maize during the lag phase. Field experiments tested 3–4 N rates at different plant densities or N timing applications over a 3-year period (2017–2019). Kernels were removed from ears collected at 9, 10, 13, and/or 17 days after silking (DAS) and treated for ECN determination via tissue dissection, staining, enzymatic digestion, and digital microscopy. Plant growth rate, plant N uptake rate, ear growth rate, and ear N allocation rate during the lag phase were studied, as well as plant growth rate during the critical period and its relationship with kernel number per plant. Low N treatments consistently reduced ECN, thereby limiting KW during this early post-silking stage. Following data normalization, the majority of final KW variation was consistently explained by ECN across all experiments and relative DAS sampling times. Nitrogen rate effects on potential KW were not associated with plant growth rate per kernel during the critical period bracketing silking. ECN was highly correlated with ear N allocation rate during the lag phase, but not with plant N uptake rate during that period. Overall, these results show that higher N availability, independently of N timing and plant density, increased final KW by enhancing the sink capacity of individual kernels (at a wide range of kernel numbers per plant) via gains in ECN during lag-period development.