The correct comparison for nutrient cycling by trees in tropical rainforests compared to temperate forests is typically that it is much shallower, because of the shallower root systems of trees.
In tropical rainforests, many trees have developed shallow root systems that spread widely near the surface, leading to nutrient cycling that is concentrated in the top layers of soil. However, the statement that the cycling of nutrients is slower due to slower decay rates in the tropics isn’t accurate as tropical ecosystems typically have rapid decomposition rates due to warm and humid conditions. Additionally, the fertility of soils in tropical rainforests is often lower than in temperate forests despite the lush vegetation.
Thus, the correct answer is that tropical rainforest nutrient cycling is generally much shallower, because of the shallower root systems of trees. The other options provided either do not accurately reflect the ecological characteristics of these forests or are incorrect.