BSC 314 Lecture Notes - Lecture 63: Algae, Germination, Mycorrhiza

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28 Jun 2018
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Plant Interactions with Other Organisms
Ecology is the study of interactions of organisms with one another as well as with their
environment. Plants, with their sedentary existence and need to attract pollinators or
prevent herbivores from consuming them whole (because they can't run away from
them), have evolved a different set of behavior patterns than have animals.
Competition
Competitionresults when an individual plant interferes with the needs of another plant
for the same environmental resource (such as light, minerals, space) or when members
of one population interfere with members of another for the same environmental
resource. In plants, competition generally is indirect, through the resource, not direct,
one on one (plants don't engage in leaf to leaf combat). Plants with the same life form ‐ ‐
and growth requirements are often in competition but surviving in slightly different
microenvironments. This generally leads to a better utilization of the resource and, with
natural selection in operation over time, a greater diversification of the community.
Secondary metabolites
Allelopathy is a particular form of directcompetition in which one plant species (or a
fungus like Penicillium) produces a substance toxic to another. In some instances, the
substance inhibits the development of the producer's own seeds or spores. The
compounds may leach from the roots into the soil or accumulate in the ground around
the plant as leaves drop and decay. Some are terpenes that volatilize and are spread
through the air as aerosols. The essential oils of members of the mint family are toxic to
numerous plants, as is the oil of black walnuts. Caffeine produced by tea and coffee
plants inhibits the growth of seedlings of many species.
Symbiosis
Chemical warfare of another kind is waged by plants that produce secondary
metabolites—chemical substances that protect the plants from being eaten by
herbivores. Plants and their predators undoubtedly coevolved, with changes in one
instigating reactions and further evolutionary changes in both.
Some of the metabolites are not merely deterrents, but are chemicals that imitate
hormones, enzymes, or other essential compounds of animal bodies. One metabolite
interferes with insect metabolism by inhibiting the juvenile growth hormone. Others, like
the alkaloids morphine and cocaine, affect the human nervous system; and caffeine,
although a stimulant to humans, in plants is toxic and lethal to insects and fungi. The
estrogens produced by some plants have no known role in the plants, but their
importance to human reproduction is well known—and a cause for concern when
humans eat vegetables.
Defense substances of a different kind protect plants from bacteria and fungi attacks.
These substances, called phytoalexins, act as natural antibiotics and protect the plant
from bacteria and fungal pathogens when leaves are damaged or stems wounded.
Nicotine in tobacco plants is synthesized in response to wounding.
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Document Summary

Ecology is the study of interactions of organisms with one another as well as with their environment. Plants, with their sedentary existence and need to attract pollinators or prevent herbivores from consuming them whole (because they can"t run away from them), have evolved a different set of behavior patterns than have animals. Competitionresults when an individual plant interferes with the needs of another plant for the same environmental resource (such as light, minerals, space) or when members of one population interfere with members of another for the same environmental resource. In plants, competition generally is indirect, through the resource, not direct, one on one (plants don"t engage in leaf to leaf combat). Plants with the same life form and growth requirements are often in competition but surviving in slightly different microenvironments. This generally leads to a better utilization of the resource and, with natural selection in operation over time, a greater diversification of the community.

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