How do deep-rooted grasses influence drought resilience in shallow soils?

• A. They shade the soil surface and reduce photosynthesis.
• B. They access deeper soil moisture, improving drought resilience and persistence when surface moisture is limited.
• C. They only affect nutrient cycling, not moisture.
• D. They decrease root depth to conserve energy.

Answer: (B)

Deep-rooted grasses improve drought resilience in shallow soils by reaching moisture that lies deeper in the soil profile. In shallow soils, rainwater and stored soil moisture near the surface are quickly depleted during dry periods, so plants with long, deep roots can tap into deeper water reserves that surface roots can’t access. That ability to access deeper moisture lets these grasses stay hydrated longer, continue transpiring, and persist through droughts. When conditions improve, they recover more quickly because part of their water supply remained intact down below. This is why deep-rooted grasses are advantageous in rangelands that experience intermittent or intense drought. The idea that shading the surface or solely affecting nutrient cycling drives drought resilience isn’t the main mechanism, and decreasing root depth would reduce access to deeper water, opposite of what deep roots provide.