Volatile compounds released by undamaged plants influence the adaptive growth strategies of neighboring plants

Plants constantly emit volatile organic compounds (VOCs) that can influence the physiology and behavior of neighboring plants. While the role of stress-induced VOCs in mediating plant-plant interactions is well established, the ecological significance of constitutive VOCs from undamaged plants remains less understood. We demonstrate that barley plants can detect the growth rate of their undamaged neighbors through constitutive VOCs and respond by adjusting their trade-off between growth and induced defense. Exposure to volatiles from cultivars with slower or faster growth triggered distinct shifts in biomass accumulation and gene expression in receiver plants, whereas exposure to VOCs from cultivars with similar growth rates elicited negligible responses. These divergent patterns reflect a trade-off between growth and induced defense, consistent with adaptive responses to anticipated competition. Our findings reveal a previously unrecognized adaptive function of constitutive VOCs in mediating receiver growth based on neighbor growth rate, emphasizing their role in shaping plant-plant interactions.