Final answer:
Higher diversity of plant species is more likely in soil derived from limestone than from granite due to the more alkaline nature of limestone, which increases the availability of crucial nutrients like nitrogen and phosphorus.
Step-by-step explanation:
There is likely to be a higher diversity of plant species in soil derived from limestone than in soil derived from granite due to the difference in soil pH influenced by the parent material. Limestone, which is rich in calcium carbonate (CaCO3), tends to create more alkaline soils when it weathers. This is because calcium carbonate acts as a weak base and can neutralize acids. In contrast, granite-derived soils are often more acidic. The acidity or alkalinity of the soil can affect the availability of inorganic nutrients, such as nitrogen and phosphorus, which are crucial for plant growth.
Acidic conditions can make it more difficult for plants to access these nutrients. Therefore, the correct answer to the question is a. The higher acidity of soil derived from granite lowers the availability of nitrogen and phosphorus to plants. Limestone-derived soil provides a more suitable environment for a wider variety of plant species because the neutral to alkaline conditions improve nutrient availability.