Mean Recipient Seedling Biomass after 12 Weeks
| Donor light treatment | Fungal connection intact (grams) | Fungal connection severed (grams) |
|---|---|---|
| Full light | 3.6 | 2.4 |
| Heavy shade | 2.3 | 2.1 |
Some soil fungi produce filaments that connect the roots of neighboring plants. Ecologists have proposed that these fungal networks can improve a young recipient plant's growth by carrying resources from an established donor plant. However, intact fungal filaments could benefit recipients in other ways, such as by altering soil conditions, without transferring resources from donors. To investigate, researchers placed donor saplings and recipient seedlings in divided containers whose mesh barriers allowed fungal filaments, but not roots, to cross. In half the containers, the researchers regularly rotated one compartment to sever the filaments. They grew some donors in full light and others in heavy shade, which reduced donor photosynthesis, while keeping all recipients under the same light and watering conditions. Based on the results, the researchers concluded that _____
Which choice most effectively uses data from the table to complete the statement?
For a command-of-evidence question involving a two-variable table, compare conditions that differ in only one variable at a time. Calculate the relevant within-row or within-column differences, avoid drawing conclusions from diagonal comparisons that change both variables, and choose language that matches the evidence's limits rather than claiming an unmeasured mechanism was proved.
Hints
Compare within treatments
Compare the two connection conditions within each row rather than comparing cells diagonally across the table.
Find each gap
Calculate the difference between intact and severed recipient biomass for full-light donors and then for shaded donors.
Consider the strength of the conclusion
Ask whether the experiment directly measured movement of resources or only measured recipient growth under different conditions.
Step-by-step Explanation
Make the relevant comparisons
To isolate the association between the fungal connection and growth, compare intact and severed connections within each donor light treatment.
Calculate the biomass advantages
Under full light, the intact-connection advantage was grams. Under heavy shade, it was only gram.
Interpret the evidence cautiously
The larger advantage under full light is consistent with the idea that donors with greater photosynthesis supplied resources through the fungal connection. However, because intact filaments could affect recipients through other mechanisms, the data do not prove that resources were transferred.