Question 33·Hard·Central Ideas and Details
Ecologist Dr. Mei Li’s recent experiments on temperate forests challenge the popular notion that the mycorrhizal “wood-wide web” generously redistributes carbon from mature “mother” trees to seedlings. Using isotope labeling, Li tracked carbon flow and found that net transfer was negligible under nutrient-rich conditions and reversed—seedlings actually exported carbon—when soil phosphorus was scarce. In controlled shade experiments, seedlings receiving supplemental light but no root contact with adults still grew as well as those linked to fungal networks, suggesting that carbon subsidy is not a prerequisite for their survival. Li concludes that while mycorrhizal connections facilitate information exchange, their role as pipelines of altruistic carbon donation is overstated.
Which claim about Li’s findings is most strongly supported by the text?
For “most strongly supported” Reading & Writing questions, first underline the specific sentence or two that directly state the key result or conclusion, then paraphrase them in your own words. Next, scan the answer choices and eliminate any that (1) contradict the passage, (2) introduce new ideas or details that weren’t mentioned, or (3) exaggerate or generalize beyond what the text says. Finally, choose the option that most closely restates the core finding or implication using different wording but no extra claims.
Hints
Locate the most important sentence
Reread the part about the “controlled shade experiments” and pay special attention to what happened to seedlings that had no root contact with adult trees.
Think about what “not a prerequisite” means
When the author says “carbon subsidy is not a prerequisite for their survival,” what does that say about whether seedlings need carbon from adults in order to live?
Check for exaggerations or new claims
Look for answer choices that go beyond what the passage says (for example, making claims about other resources or exact conditions not directly tested). Those are unlikely to be correct.
Watch the direction of the evidence
Does the passage support the idea that adult trees behave altruistically, or does it challenge that idea? Eliminate any option that contradicts the author’s conclusion.
Step-by-step Explanation
Identify the key experimental result about seedlings
Focus on the sentence about the shade experiments: “seedlings receiving supplemental light but no root contact with adults still grew as well as those linked to fungal networks, suggesting that carbon subsidy is not a prerequisite for their survival.”
The critical idea is that seedlings without root contact (and therefore without carbon transfer from adults) still grew just as well as those connected by fungal networks.
Restate what that result implies
If seedlings grow equally well with or without fungal carbon transfer, then getting extra carbon from adult trees through the fungal network cannot be required for them to live.
The author even paraphrases this by saying “carbon subsidy is not a prerequisite for their survival,” which means carbon help from the network is not essential for seedlings to survive.
Compare each answer choice to the passage
Now match the choices to what the passage actually says:
- One choice should reflect that seedlings do not depend on carbon from fungal networks to survive.
- Watch out for answers that:
- Claim the opposite of the findings (that altruism is confirmed).
- Introduce new, untested ideas (like other resources beyond carbon).
- Misread the carbon transfer patterns (who sends carbon to whom, and under which conditions).
Select the answer fully supported by the text
The only option that matches the experimental result that seedlings survived and grew just as well without carbon from adult trees is:
They indicate that carbon transfer via fungal networks is not essential to seedling survival.