For table-based command-of-evidence questions, identify the precise comparison and any threshold defined in the passage before evaluating the options. Compare values within the correct groups, and avoid conclusions that change what the table measures—for example, interpreting a ratio as an absolute amount.
Hints
- Hint 1
Use within-species comparisons
For each grass, compare the two treatment values with that grass's own standard-condition value.
- Hint 2
Check reliability
Calculate each difference and determine whether it reaches the stated threshold of 0.10.
- Hint 3
Interpret the measurement carefully
Distinguish between an increase in a root-to-shoot ratio and an increase in the absolute amount of root biomass.
Step-by-step
- Step 1
Identify the required comparisons
Compare each treatment value with the standard-condition value for the same species. A change must be at least 0.10 to count as reliable.
- Step 2
Calculate the changes
For prairie dropseed, the low-nitrogen change is , while the low-water change is . For sideoats grama, the low-nitrogen change is , while the low-water change is .
- Step 3
Apply the reliability threshold
The two changes of 0.45 are reliable, but the two changes of 0.04 are not. Because the table reports ratios, these changes concern relative allocation rather than absolute root biomass.
- Step 4
Select the supported conclusion
The correct answer is low nitrogen reliably shifted prairie dropseed, but not sideoats grama, toward greater relative belowground allocation, whereas low water reliably shifted sideoats grama, but not prairie dropseed, in that direction.