Temporal pattern of biomass partitioning to apical ear in maize plant hierarchies under contrasting resource availabilities

Most studies in maize (Zea mays L.) focus on biomass partitioning to the ear (BA_E) during the critical period for kernel setting (from −220 +100°Cd from silking; R1). However, early-established interplant variability of growth (around V7) affects both plant and ear growth during this period, influencing kernel setting across plant hierarchies. Delays in silk extrusion are often linked to reduced BA_E due to low plant growth just before R1. This study examined whether variability of BA_E and thermal time (TT) to R1 among plants is pre-conditioned early in the cycle (close V7). Two maize hybrids with contrasting tolerance to crowding stress (AX820: high, AX877: low) were grown in field conditions under combinations of stand densities (9 and 12 plants m⁻²) and nitrogen levels (0 and 200 kg N ha⁻¹) or water availabilities (well-watered and water deficit). Plants were sampled from V7 to 100°Cd after R1 and classified into dominant, intermediate, and dominated hierarchies. For each hierarchy, BA_E was estimated as the ratio of ear biomass to plant biomass. Abiotic stresses increased interplant variability, reduced growth and BA_E, and delayed TT to R1. Differences on BA_E patterns among plant hierarchies were analyzed using ANOVA of linear regressions of natural log of BA_E vs TT from sowing. Dominated plants showed longer TT to R1 due to a delayed onset of active BA_E. A common BA_E pattern emerged when TT was aligned with R1 for each hierarchy, suggesting an ontogenic effect on BA_E.