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CELPIP Practice Reading: Reading for Information ID: #63115 Medium Mycorrhizal fungi and tree nutrient networks

Read the following passage.

A. Mycorrhizae are partnerships between plant roots and fungi, and the name itself means fungus root. Scientists think about 95 per cent of all seed plants have them on their roots, and both partners probably need them to survive in the wild. The plant gains a better ability to absorb minerals such as phosphorus and nitrogen, and it resists root diseases more strongly. In return, the fungus takes sugars directly from the plant, so it does not have to compete with other microorganisms for its food.

B. These partnerships take several forms. The most widespread form, called arbuscular mycorrhizae, is found in about 90 per cent of seed plants, and in it the fungus grows inside the cells of the root's outer layer. In the other main form, ectomycorrhizae, the fungus wraps the root in a thick sheath that often makes it several times wider, and its threads pass between root cells without entering them. This form is especially well developed in Canada, where most forests are dominated by trees that carry it.

C. The fungi grow many branching threads, called mycelium, that spread out from a root tip and can join the roots of other trees and plants. Plants linked in this way share what scientists call a common mycorrhizal network. In 1997, a team including Suzanne Simard, now a forest ecologist at the University of British Columbia, reported in the journal Nature that carbon moved in both directions between birch and Douglas fir seedlings in the field. The Douglas fir gained more than it gave, and its net gain averaged 6 per cent of the carbon it took up through photosynthesis. Such a forest network is now widely known as the wood-wide web.

D. Simard now leads the Mother Tree Project, a 100-year study of different harvesting approaches in the Douglas fir forests of British Columbia's Interior. How much the networks matter is still debated, however. In 2023, Justine Karst of the University of Alberta and two colleagues reviewed the field evidence. They judged that claims that the networks are widespread and that they pass useful resources to seedlings are not well supported. They also found no peer-reviewed evidence that mature trees send extra resources to their own offspring, and concluded that knowledge of the networks is too sparse and unsettled to guide forest management.

E. Not given in any of the above paragraphs.

Decide which paragraph, A to D, has the information given in each statement below. Select E if the information is not given in any of the paragraphs.

 - 1. A 2023 review found no published proof that older trees favour their own young when sharing resources.

 - 2. An early field experiment showed that the flow of carbon between two tree species went both ways.

 - 3. In the most common type of partnership, the fungus lives within cells inside the root.

 - 4. Once fungal strands from one plant reach the roots of another, the two become connected.

 - 5. Partners that grow inside root cells deliver more nutrients than the kind that coats the outside of roots.

 - 6. The fungus receives its food straight from the plant instead of competing for it with other tiny organisms.

 - 7. A century-long project is looking at several methods of logging.

 - 8. In one type of partnership, a fungal covering can make a root a few times broader.

 - 9. Most of the money for the century-long forest project comes from timber companies.

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