Intraspecific competition drives orthogonal variation in root exudate metabolic and functional traits in seedlings of a dominant species

Abstract Classical plant functional traits, often limited by intercorrelation and incomplete capture of dynamic variation, are insufficient for fully predicting ecological responses to environmental change. Quantifying independent functional dimensions, particularly those reflecting molecular and biochemical processes, is therefore essential for a comprehensive understanding of plant ecology. We adapted the well‐established community‐weighted mean (CWM) concept from ecology to metabolomic data, developing a framework to quantify metabolic functional traits based on the intrinsic chemical properties of metabolites. We applied this framework to root exudate metabolomics of Haloxylon ammodendron seedlings undergoing intraspecific competition. Our results show that intraspecific competition significantly altered the root exudate metabolome composition. We characterised the chemical space of identified metabolites using molecular descriptors, revealing three core dimensions of variation: molecular size/hydrogen bonding, acidity/structural complexity and hydrophobicity/saturation. Plant metabolic functional traits, quantified as CWMs of these chemical properties, varied significantly with competitive interaction, exhibiting distinct adaptive patterns across treatments, ranging from investment in defence/allelopathy to nutrient mobilisation or aggressive nutrient acquisition. Crucially, correlation analyses showed no significant relationship between metabolic CWMs and classical traits, and integrated principal component analysis further revealed their orthogonal separation in multivariate space. Synthesis : These findings demonstrate that metabolic CWMs represent a novel, independent functional dimension. This highlights the power and potential of integrating molecular‐level functional traits to enhance our understanding of plant ecological strategies and phenotypic plasticity, particularly in capturing intraspecific variation.