Nitrogen Form Substitution Enhances Growth and Carbon Accumulation in Maize

Abstract Sugars are essential for plant development, and nitrogen (N) availability regulates their distribution, influencing overall growth. However, the mechanisms underlying carbon (C) assimilate allocation and utilization in response to changed N forms remain unclear. This study examined the effects of nitrogen form substitution (NFS) on C accumulation and utilization in hydroponically grown inbred mini-maize (TX-40 J). Maize seedlings were divided into three treatment groups: T1 (1 mM NO₃⁻), T2 (1 mM NH₄⁺), and T3, where 1 mM NO₃⁻ was substituted with 1 mM NH₄⁺ (NFS) at 10 days after seedling transfer (DAT). The results showed that NFS led to a significant ( P ≤0.05) reduction in total sucrolytic activity by 27% in leaves and 21% in roots, resulting in a lower hexose-to-sucrose ratio. Despite this, NFS enhanced shoot biomass by 30%, root biomass by 24%, and total biomass by 28%, suggesting improved sucrose utilization and increased competition for assimilates. Root-to-shoot biomass allocation was particularly enhanced under NFS conditions. Additionally, starch and sucrose accumulated at lower levels in leaves under NFS compared to other N treatments. Starch was predominantly stored in the leaf tips, whereas sucrose accumulated in the leaf sheath. This spatial sucrose and starch distribution suggests that C buildup was not due to impaired C assimilation but rather inefficient C utilization in sink tissues. These findings provide new insights into how NFS influences C allocation between leaves and roots, promoting growth and stress adaptation in maize. Understanding the role of C partitioning under NFS conditions may help optimize plant growth and improve nutrient use efficiency under N deficiency conditions.