Altering Source‐Sink Relationships in Prolific Maize Hybrids: Consequences for Nitrogen Uptake and Remobilization

Abstract

Competition between grain and roots for photoassimilates may reduce post‐anthesis N uptake (Na), thereby limiting grain production of prolific maize (Zea mays L.). Field experiments were conducted to determine if this competition was minimized during the selection for new high‐yielding prolific lines, providing a plausible physiological explanation for the improved grain yields. The dry matter (DM) and N accumulation and partitioning of two high‐yielding and three low‐yielding prolifics were compared under full pollination, limited pollination of the apical ear, or no pollination. The following year, one high‐yielding and one low‐yielding hybrid were grown at 34 000 and 45 000 plants ha−1. Fully pollinated, high‐yielding hybrids averaged 74% more grain weight (Gw) than low‐yielding hybrids. A highyielding hybrid produced 71% more Gw under full pollination than with apical ears only pollinated, while limiting pollination had little effect on low‐yielding hybrids. Greater contributions of subapical ears in new prolifics were attributed to greater kernel weight and number, which were positively correlated with post‐anthesis DM accumulation (Twa). The DM partitioning to vegetative tissue [Twa − Gw] is indicator of photosynthate availability for plant functions during grain‐filling. Greater [Twa − Gw] occurred at the low plant density and with limited pollination, and this was positively related to Na while inversely related to Nr. The high‐yielding hybrids maintained Ta and Na during multiple ear development. These results suggest Na is regulated by the ear sink size relative to photosynthate supply.