This particular biome is characterized by abiotic factors, which are non-living characteristics such as temperature, humidity, rainfall, and soil type. In the case of the Amazon rainforest, it's characterized by abiotic factors, like nutrient-poor soil, heavy rainfall, humid air, and warm temperatures.
Climate, soil type, precipitation, temperature and sunlight are all abiotic factors that determine the composition of a rainforest, including the major differences between rainforests in tropical and temperate regions of the globe.