This study investigates the role of negative plant-soil feedback in maintaining tree species diversity in tropical forests. The authors conducted reciprocal shade-house and field experiments to test whether conspecific tree seedlings grow better when grown with heterospecific adult trees, indicating negative feedback. The results show strong evidence of negative plant-soil feedback mediated by soil biota, with tree species exhibiting stronger negative feedback being less common as adults. Above-ground enemies contributed little to the observed negative feedback. Simulation models confirmed that the strength of local negative feedback is sufficient to influence community-wide patterns in tree species abundance. The findings suggest that plant-soil feedback is an important mechanism for maintaining species diversity and relative abundance in tropical forests.This study investigates the role of negative plant-soil feedback in maintaining tree species diversity in tropical forests. The authors conducted reciprocal shade-house and field experiments to test whether conspecific tree seedlings grow better when grown with heterospecific adult trees, indicating negative feedback. The results show strong evidence of negative plant-soil feedback mediated by soil biota, with tree species exhibiting stronger negative feedback being less common as adults. Above-ground enemies contributed little to the observed negative feedback. Simulation models confirmed that the strength of local negative feedback is sufficient to influence community-wide patterns in tree species abundance. The findings suggest that plant-soil feedback is an important mechanism for maintaining species diversity and relative abundance in tropical forests.