Significance: Symbiotic dinitrogen (N ₂ )-fixing trees fulfill a critical function in tropical forests by bringing in new nitrogen, yet it remains unclear how they overcome constraints by highly weathered, nutrient-poor tropical soils. We advance forest biogeochemistry and microbial ecology with the discovery from field trials in Panama that fast-growing N ₂ -fixing trees in tropical forests exhibit accelerated mineral weathering and distinctive soil metagenomes that improve their access to inorganic nutrients in nutrient-poor soils. Furthermore, we show that N ₂ -fixing trees exert similar effects on non-N ₂ –fixing trees nearby thus having previously overlooked community-wide effects on tropical forest nutrient cycling. These results offer insights into the role of N ₂ -fixing trees and their associated microbiomes in safeguarding the function of tropical forests within the global biosphere.