Volatile organic compound exchange as a potential source of experimental bias in plant biostimulant and elicitor trials

Abstract Plant primary and specialized metabolism form an integrated biochemical network that coordinates growth, development, defense, stress tolerance, reproduction, and ecological interactions. This review examines the historical transition from viewing specialized metabolites as metabolic by-products to recognizing them as regulated adaptive compounds derived from primary metabolic precursors. It discusses the major classes and functions of specialized metabolites, their energetic and regulatory costs, and the metabolic trade-offs associated with elicitation. Particular attention is given to volatile organic compounds (VOCs), which mediate plant–plant and plant–microorganism communication. Evidence synthesized from 55 publications, including primary experimental studies and reviews, perspectives, commentaries, and addenda, demonstrates that VOC exposure can modify defense priming, growth, root architecture, nutrient acquisition, stress tolerance, and microbiome composition in neighboring plants. Building on this evidence, the review examines whether unintended VOC exchange between experimental treatments and controls may represent a source of experimental interference in biostimulant and elicitor trials. These observations raise the possibility that untreated plants sharing airspace with treated, stressed, or microbe-associated plants may, under conditions permitting biologically relevant VOC exposure, become physiologically modified receivers rather than fully independent negative controls. The magnitude and experimental relevance of this effect depend on VOC identity and concentration, exposure duration, donor–receiver distance, airflow, ventilation, plant genotype, developmental stage, and environmental conditions. Consequently, uncontrolled VOC exchange has the potential to reduce treatment contrasts, increase variability, and contribute to false-negative or false-positive interpretations under specific experimental conditions. Future experimental protocols should therefore consider VOC movement as a potential experimental factor and report the environmental and spatial conditions required to evaluate the likelihood of cross-treatment exposure.