Week 2: Plant Environments
-The peregrine falcon is quite in a range across North America, and you can see it in the high
arctic. You can also see Falco peregrinus in the desert.
-Dandelions are another versatile species.
-However, most species are quite limited in distribution.
-GR describes the limits that contain the area graphically, ie boundaries. Where a species is
What factors are limiting to organisms?
A plant environment is different from an animal environment. From a time that a plant is a seed
to a seedling, to a sapling(young plant) to an adult plant, the environment is what happens
around the plant during all those times.
-Plants are sessile(fixed) organisms.
-Plant environments are localized. It does not move in space, as most animals do.
*factors that are part of the plant environment*
1. Physical factors 1) climate. Insolation(solar). See slide. In the arctic any plant growing there
has high winds.
How do most physical factors occur?
The occur as gradients. Ie as we move north, we experience declining levels of sunlight. That’s a
gradient. If ur moving up a hill, we experience more wind and more exposure to wind.
-We need to know this to explain plant distribution.
-relationship between gradient and plant depends on plant physiology. Re is too much so it
goes downhill and there is an inverse relationship.
-The optimim level depends on the species and its adaptations.
-Tolerance range: the idea of tolerance limits. If you have reached a low point in moisture for
example, that is going to affect the plant. Tolerance ranges explain the gradient, and the range
of tolerance. An increase in moisture for example, is the gradient, and as we increase moisture,
the plant growth increases. At low levels there isn’t enough.But once we reach optimum, there
is too much.
-This is the most important factor for photosynthesizing plants. Light is the energy source for
photosynthesis and promotes gas exchange between different plant parts.
-Light varies from equator to pole. Variation in plants is not significant. Instead, the local scale
of light variations are critical in determining whether a plant will grow at this site or this site.
-We get large scale local variations of light that are critical in explaining local species. -Plants can tolerate moisture loss on south facing slopes.
-you can get plants that cope with low light(forest bottom) or plants that cope with high
-At the canopy, you have differences in the light level.
What is the interaction between light and a plant species’ physiology?
-2 cals/cm sq/min is what gets reflected off earths atmosphere, just half of that comes back to
PAR(Phar)-Photosynthetic active radiation
-Stuff that vascular plants use when they photosynthesize
-This is a smaller portion of the light spectrum when it is received
-red light is very critical and important for chlorophyll formation. PAR reflects the most green
-Red and a bit of blue light is important for plants.
Photosynthesis: see equation. Energy from sun(hv) is used to produce glucose oxygen and
-Desert plants use their stems to photosynthesize
What is the relationship between increasing light intensity and photosynthesis?
-It is a bellcurve. After the optimum point, It goes down. Y axis=rate of photosynthesis
compensation point? It’s right at the top. It is the point at which there is too much sunlight. The
zone of optimum is the saturation point, at which the plant can no longer make any use of the
google: photorespiration vs photooxidation.
Compare shade-tolerant and shade-intoleratn species in Eastern forests
-Shade tolerant species? It grows well in the shades of other plants and the forest floor. A
species of intermediate shade tolerance needs more light intensity.
Shade intolerant species? They need more light intensity, and have a higher saturation point.
They do best at 20-30% full sunlight.
-spring ephemerals(flowers) such as trout lily, fleur de lys, etc..
Adaptations for shade-intolerant species? Plant are adapting to be shade intolerance by having