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Mutualisms Part 2
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Includes mutualism in community structure, mycorrhiza in communities of plants, coral reef mutualism, and sanctions which follows on from a previous lecture.
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EcologyLecture 6 Mutualisms 2 03/03/21
Another example of sanctions
- Bever et al. (2009) studied mutualistic association between plants and arbuscular
mycorrhizal fungi.
- The basic premise was that if a fungus reduces the benefits it provides to a plant, the plant
should respond by providing smaller benefits (sugars from photosynthesis) to the fungus.
- Bever et al (2009) utilised the fact that alliums are monocots. In monocots, internal resource
movement is not constrained by vascular architecture, and therefore the products of
photosynthesis can potentially be moved to any part of the plant.
- The group used a split root design in which the wild onion root was divided equally between
two halves of a pot. One side of the pot contained the beneficial Glomus ‘white’ fungus,
whilst the other half contained Gigaspora margarita – which appears to provide no benefits
to the onion plant. This was figured out by the fact that the onions grew better with the
Glomus (Gl) fungus, and there was no change between the control and the Gigaspora (Gig).
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- After 9 weeks, Bever et al. then covered the onion shoots with
bags which contained 14CO2 (radioactive carbon). They then
followed the fate of the 14C in the roots of the plants and the
hyphae of the fungi after 2h, 1, 2 and 4 days.
- As predicted, more sugars with the radioactive carbon went to
the roots with the beneficial Glomus fungus. The hyphae of the
Glomus assimilated more of the 14C also.
Mutualism and community structure
- Mycorrhiza actually refers to the plant-fungi association, derived
from the Greek mykes “fungus” and rhiza “root”.
- There are two key types: arbuscular mycorrhiza – characterised by the intracellular
colonisation of plant root cells by the fungi; and ectomycorrhiza – in which the colonisation
of root tissue by fungi is extracellular.
- Mycorrhizal fungi may affect plant species diversity.
- In one large scale field trial, researchers manipulated the number of mycorrhizal fungi found
in soil in which identical mixtures of seeds of 15 plant species had been sown.
- As the number of mycorrhizal fungi increased, so did the plant species diversity, shoot
biomass, root biomass, plant phosphorous content, and fungal hyphal length.
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