Although tropical rain forest plants grow vigorously, the clay soils of tropical rain forests are very low in mineral nutrients. A. Clays with poor mineral-binding capacities plus low levels of organic compounds that result from rapid decomposition produce compacted soils that are highly vulnerable to rain leaching. B. Plants are able to tolerate the high levels of aluminum in tropical rain forest soils only because of bacteria and fungi that neutralize aluminum while absorbing and transferring phosphorus. C. Because water does not penetrate deep into tropical rain forest soils, most trees growing in such soils have shallow feeder roots that spread over large areas in search of adequate moisture. D. The delicate fungal hyphae that extend throughout most tropical rain forest soil help maintain soil quality by transferring excess nutrients from plant tissues back into the soil. E. Tropical rain forests have evolved closed nutrient systems, in which plants and their fungal partners transfer mineral nutrients among organisms with little leaching through to the soil. F. Nitrogen-fixing bacteria in the soil and within the roots and root nodules of many plants provide rain forest plants with the nitrogen needed to help compensate for poor soils.