On a trip to the Southwest, you and a friend collect some seeds from a piñon, which is a type of pine tree. Your friend also gathers a small bagful of soil from under the piñon tree. Back home, both of you plant your seeds in commercial sterilized potting soil, but your friend adds a spoonful of the collected dirt to each of her pots. Her seedlings do better than yours. Which of the following is the likeliest explanation?

Question

Quizplus · Accepted Answer

The likeliest explanation is that the soil from the Southwest probably contained fungi able to establish a mycorrhizal association with the seedlings' roots. Mycorrhizal fungi form a mutualistic relationship with plant roots, providing them with increased access to water and nutrients, such as phosphorus, in exchange for carbohydrates from the plant. Commercial potting mix may not contain these beneficial fungi, which could explain why the seedlings in the friend's pots did better.

On a Trip to the Southwest, You and a Friend