ISA Certified Arborist Practice Exam

Which soil zone is defined as the area immediately surrounding roots?

1. Macropores

2. Clay

3. Rhizosphere

4. Meristems

The correct answer is: Rhizosphere

The rhizosphere, or root zone, is the thin layer of soil immediately surrounding plant roots. This is where most of the biological and chemical interactions between roots and soil occur, and where most of the nutrients are absorbed by the roots. Macropores, or large openings in the soil, are not specifically defined as the area surrounding roots and can occur at different depths in the soil. Clay is a type of soil texture and is not specific to the area surrounding roots. Meristems, or actively dividing plant cells, are not a type of soil zone and are found within the plant itself. Therefore, the option C, rhizosphere, is the most accurate and relevant answer to the question.