1H-NMR metabolomic profiling reveals asymmetric metabolic responses of Cyperus rotundus and Sorghum bicolor in co-culture competition

This study investigated the competitive interaction between Cyperus rotundus L. (CR) and the allelopathic crop Sorghum bicolor L. Moench (SB) during seedling development, combining morphological measurements with quantitative ¹H-NMR-based root metabolomic profiling. The experiment was conducted on 8 plants per experimental condition, and data were analysed by univariate statistical testing combined with principal component analysis (PCA) of the metabolomic profiles. SB exhibited significant reductions in plant height, leaf number, root length and root biomass, whereas CR growth parameters remained unaffected, revealing a marked asymmetry under competitive conditions. ¹H-NM metabolomic analysis identified 40 metabolites in CR and 38 in SB. Multivariate PCA and Spearman correlation analyses demonstrated a systemic metabolic depletion in SB across essential and non-essential amino acids, carbohydrates, phytosterols, organic acids, and its key cyanogenic glucoside, dhurrin. This widespread downregulation points to severe nitrogen (N) limitation and a growth-defense trade-off in SB driven by competition with CR. Conversely, CR displayed strong homeostatic metabolic resilience, maintaining its primary root metabolome unaffected. The only significant change observed in CR was a marked reduction in γ-aminobutyric acid (GABA) levels, indicating uncompromised TCA cycle flux and energy status. Furthermore, correlated metabolic patterns in CR (e.g., glutamine, galactose, and phenylalanine) suggest enhanced N uptake efficiency and active cell wall remodelling to support root expansion. Taken together, these findings indicate that despite SB known allelopathic potential, CR exerts superior competitive suppression at the seedling stage, a process likely mediated by belowground competition that remains complex and largely unexplored.