Cultivar mixtures increase crop diversification and grain yield stability.  Achieving high grain yield and nitrogen use efficiency (NUE) with environmentally friendly practices is a major challenge, but it is currently unclear whether maize cultivar mixtures can improve NUE.  A two-year field experiment was conducted using two maize cultivars with different roots angles and leaf angles planted in monoculture or in mixtures under four nitrogen levels N0 (0 kg N ha^–1), N140 (140 kg N ha^–1), N280 (280 kg N ha^–1) and N340 (340 kg N ha^–1).  Cultivar mixtures significantly increased light interception of the middle canopy, dry matter accumulation and total root length under N0, N140, and N280 conditions.  Light interception of the middle canopy was positively related to dry matter accumulation and thus increased grain yield.  In addition, light interception of the whole canopy was positively related to total lateral root length, while the greater total lateral root length of outer nodal roots significantly improved nitrogen accumulation and NUE.  Thus, cultivar mixtures promoted an optimal canopy structure and good root growth, thereby improving grain yield and NUE.  These findings deepen our understanding of the facilitating effect of canopy structure and root traits of cultivar mixtures on the combined promotion of grain yield and NUE. 

Waterlogging stress significantly impairs plant growth and reduces crop yields.  Spermidine (Spd), functioning as a second messenger, demonstrates positive effects on plant growth under waterlogging stress conditions.  However, the molecular mechanisms by which exogenous Spd application alleviates waterlogging stress remain unclear.  This study employed physiological analysis and multi-omics approaches to investigate the effect of Spd application on waterlogging stress.  The application of Spd enhanced the expression of genes related to light-harvesting complex (LHC), photosynthesis, and starch-related pathways, while inhibiting chlorophyll degradation and maintaining higher photosynthetic rates, thereby increasing biomass accumulation under waterlogging stress.  The activation of genes associated with trehalose and Spd biosynthesis resulted in elevated accumulation of trehalose and endogenous Spd.  The inhibition of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO) expression contributed to reduced ethylene emission, enhancing maize resistance to waterlogging.  Following Spd application, auxin-related genes were up-regulated and indole acetic acid (IAA) content increased, promoting cell elongation in maize and maintaining normal growth under waterlogging stress.  Additionally, the upregulation of lipid-related genes led to increased lipid content, protecting cell membranes under waterlogging conditions.  These molecular and physiological modifications collectively enhanced resistance to waterlogging stress.  These findings advance our understanding of Spd’s regulatory roles in mitigating waterlogging damage and provide valuable insights for breeding waterlogging-tolerant maize varieties.