Social physiology of cherry tomato and bell pepper: Friend or foe across growth stages and environments

• Root exudates varied with neighbor identity, showing recognition effects. • Neighbor genetic relatedness impacts plant growth, fruit yield and quality. • Neighbor effects on plant traits consistent across growth stages and environments. We investigated aboveground and belowground plant responses to neighbors with varying degrees of relatedness from the early vegetative to fruiting stages. Cherry tomato ( Solanum lycopersicum L . ) and bell pepper ( Capsicum annuum L . ) were grown individually (C and B, respectively) and paired based on high (CC and BB) and low (CB) degrees of relatedness, in rhizoslides, pots, and a greenhouse. In the CB pairing, cherry tomato consistently exhibited enhanced net CO 2 assimilation, stomatal conductance, chlorophyll content, height, stem diameter, dry weight, and increased root thickening. In bell pepper, these traits were impaired and showed increased fine root proliferation; however, under greenhouse conditions, it allocated more resources to root development, forming thicker roots. Neighbor presence and relatedness significantly impacted fruit quantity and quality: cherry tomato in CB pairing yielded higher total and export-grade fruit (by 32 %), whereas bell pepper produced the lowest yields (by 31 %) but maintained stable sugar content. Root exudate carbon concentrations were highest in CC and BB pairings, and elevated in the CB pairing compared to individuals, indicating recognition of neighbor identity. The effects of neighbor recognition and genetic relatedness were species-specific and consistent throughout growth, offering insights into their ecological roles in plant interactions and highlighting the potential of strategic species pairing in intercropping systems to enhance crop productivity.