Chapter 6
Plant Adaptations to the Environment
Required Reading Additional Reading (2-3 Quiz questions from these sources)

Chapter 6 in Elements of Ecology.

Text, images and captions on this page.

Sections of Chapter 6 that we are NOT covering:

  • 6.5 -- The Process of Carbon Uptake Differs...
  • 6.10 -- The Link Between Water Demand and ...
  • 6.13 -- Wetland Environments Present...
  • Researcher Profile | Kaoru Kitajima
  • Quantifying Ecology 6.1 | Relative Growth Rate


Study Questions / Quiz Prep. (Consult Required Reading and lecture notes for answers.)

  1. What is the ultimate source of carbon from which all life is constructed?
  2. What is an autotroph?
  3. What is a heterotroph?


  1. Photosynthesis is responsible not only for the _____________________ we animals consume, but also for the ______________________ we breathe.
  2. The initial product of photosynthesis is not a sugar. It is a 3-carbon molecule that can be chained together to make sugar and what other kinds of molecules?

Carbon Balance

  1.  “Carbon balance” is an expression for comparing the relative activities of photosynthesis and respiration. How does the plant achieve a positive carbon balance? Negative carbon balance?
  2. What happens to a plant operating at a continuously negative carbon balance?


  1. What is the carbon balance at light levels below the light compensation point? Above the light compensation point?
  2. Can plants ever get too much light? If so, what is the result?


  1. What are leaf stomata? Leaf stomata control the flow of what?
  2. As CO2 diffuses into the leaf through the stomata, _____________________ diffuses out through the same opening.
  3. What balance must be achieved in the operation of the stomata?


  1. As the environment warms up, the leaf warms up and photosynthesis increases… to a point. What happens when the leaf gets too hot?
  2. How do leaves on terrestrial plants dissipate heat to the surrounding environment?
  3. How can leaf shape make a difference in the efficiency of heat loss?
  4. Does leaf shape influence heat loss by convection, or heat loss by evaporation, or both?

Carbon Allocation

  1. Leaf tissue, stem tissue, root tissue – what are they good for?
  2. Increased allocations towards leaf tissue results in increases in___________________.
  3. Increased allocations towards stem and root tissues results in increases in what?
  4. Why not just allocate all carbon exclusively for leaf production?

High Light vs. Low Light

  1. What are the photosynthetic tradeoffs made by shade-tolerant plants as compared to the tradeoffs made by shade-intolerant plants?

Diversity of Leaf Morphology

  1.  Figure 6.11. What is the explanation for differences in leaf morphology for leaves from the top canopy compared to leaves from the bottom canopy?
  2. Are such differences the result of evolutionary adaptation or physiological adaptation?

Dealing with Saltiness

  1. From the presentation page: How do salt grass (Distichlis), and pickleweed (Salicornia) differ in their abilities to cope with high salt environments?

Water Demand and Temperature (NOTE: Disregard all discussions involving C3 , C4 and CAM biochemical pathways)

  1. In tropical regions with distinct wet and dry seasons, some species of plants drop their leaves at the onset of the dry season. How might this be a rewarding behavior? What about the carbon balance?
  2. Plants may respond to a decrease in available soil water by increasing the allocation of carbon to the production of __________________ while decreasing the allocation of carbon to ________________.
  3. How might this be a rewarding allocation pattern?

More on the Topic of water Conservation in Hot and Arid Environments

  1. Some plants have leaves covered with light hairs (white sage, jojoba). How might this be a rewarding feature for plants living in hot, dry environments?
  2. Some plants have leaves coated with waxes and resins (monkeyflower, black sage). How might this feature be rewarding for plants living in hot, dry environments?

Coping with Extremely Cold Winters

  1. Some plants use chemical techniques for frost hardening in response to cold weather. Name one plant that does this?
  2. Some plants avoid the high costs of frost hardening by doing what instead?
  3. We have at least one Maple tree on the Fullerton College campus. Every winter it loses its leaves – as if it lived in cold Vermont. But the winters are mild here. Why does this tree still lose its leaves in winter?


  1. Why is nitrogen such an influential nutrient in photosynthesis and overall leaf function?
  2. What are some adaptations that allow some species of plants to be successful despite low nutrient soils?
  3. Tropical rain forest soils often are nutrient poor. Many tropical rain forest trees have large shallow root systems. Why would such a system be more rewarding than a deeper system of roots?


Basic Plant Biology

Tree Biology Diagram
Image source: Tom Morris

Carbon Balance

Carbon balance is the difference between the uptake of carbon by photosynthesis minus the loss of carbon by cellular respiration.

Carbon balance = Photosynthetic uptake of CO2 minus respiration output of CO2

Positive carbon balance - achieved when the amount of photosynthetic uptake of CO2 is greater than the amount of CO2 released by cellular respiration.

During positive carbon balance, the plant is:

  • adding to reserves
  • putting on weight
  • growing larger

Negative carbon balance - achieved when the amount of photosynthetic uptake of CO2 is less than the amount of CO2 released by cellular respiration.

During negative carbon balance, the plant is:

  • depleting reserves
  • losing weight
  • not growing larger

When conditions for photosynthesis are good, plants operate in a positive carbon balance.

When conditions for photosynthesis are bad, plants operate in a negative carbon balance.

Environmental Circumstances that Influence Photosynthesis

Environmental Circumstance Good for Photosynthesis Bad for Photosynthesis
Light Availability Normal bright sunlight Darkness, artificial extra-bright light
Temperature Temperatures above freezing and below 110 degrees F Temperatures freezing and below. Temperatures above 110 degrees F
Water Availability Abundant water, full hydration Water shortage, less than full hydration


Positive Carbon Balance Negative Carbon Balance

Summer in Vermont
Image source: Unknown

Winter in Vermont
Image source: Unknown

Sonoran Desert. Spring following winter rains
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Mojave Desert. Late summer after many months of drought.
Image source: Unknown



This graph shows photosynthetic activity (CO2 uptake, Y-axis) as a function of Light intensity (X-axis).

Note that when there is no light, there is no photosynthetic activity, and CO2 uptake is negative (negative carbon balance). This means that more CO2 is being given off than taken in. As light increases, CO2 uptake eventually exceeds CO2 output (positive carbon balance).

Eventually, despite increased light intensity, CO2 uptake levels off (saturation).
Image source: Pearson Education, Inc.


This graph compares photosynthetic activity (CO2 uptake) between Sun-Grown plants and Shade-Grown plants.

Note that at low light levels, shade-grown plants outperform sun-grown plants. But at higher light levels, sun-grown plants outperform shade-grown plants.
Image source: Pearson Education, Inc.

Bromeliad. A plant that does very well in shady environments.
Image source: Unknown

Sunflower. A plant that does very well in sunny environments.
Image source: Unknown



Drawing of cross-section of a stoma ("stomata" is plural).
Image source: Pearson Education, Inc.

A scanning electron micrograph of a stoma on the underside of a leaf.
Image source: Unknown



Stomata (plural for "stoma") are openings in a leaf that, when open, increase the rate of CO2 uptake when conditions for photosynethesis are good. Increased CO2 uptake can increase photosynthesis performance.

But there is a cost to this perfomance feature -- water loss. As more moist surface area is exposed for CO2 uptake, moisture from the exposed cavity is lost through the stomata. This is a tradeoff. For plants living in moist conditions, this expense is manageable. But for plants living in arid conditions, the loss of water is too costly to justify the improved performance in photosynthesis.
Image source: Tom Morris



Reducing water loss in hot, dry climates

African Savanna - tropical. Hot all year long. Rainy season, followed by months of drought.
Image source: Unknown


Chaparral plant community - temperate. Cool winters with about 13 inches of rain, followed by months of drought and hot summers.
Image source: Unknown


Coastal Sage Scrub plant community - temperate. Cool winters with about 13 inches of rain, followed by months of drought and hot summers.
Image source: Unknown


Desert Scrub plant community, Mojave Desert - temperate. Cool/Cold winters with about 7 inches of rain, followed by months of drought and extremely hot summers.

Yuccas continue to photosynthesize using chlorophyll-containing stems while the leaves of surrounding plants are mostly dried up and dead. - temperate
Image source: Unknown


White Sage of the Coastal Sage Scrub plant community. Light colored leaves reflect incoming sunlight, thereby reducing the plant's heat uptake.
Image source: Unknown


Monkey Flower of the Coastal Sage Scrub plant community. A thick waxy coating on the leaves helps reduce water loss in this arid environment.
Image source: Unknown


Black Sage of the Coastal Sage Scrub plant community. A thick waxy coating on the leaves helps reduce water loss in this arid environment.
Image source: Unknown


Jojoba of the Sonoran Desert. Light colored leaves reduce heat uptake, by reflecting sunlight.

In addition, the vertical orientation of leaves helps reduce the amount of leaf surface exposed to the sun during the hottest part of the day when the sun is directly overhead.
Image source: Unknown


Cardone cactus in Baja Mexico - Sonoran Desert. Light coloration helps reduce heat uptake.

Vertical growth pattern reduces sun exposure (and heat uptake) at mid day when sun is hottest.

Tall growth places the bulk of the plant above the baking desert floor, and high enough for cooler breezes.

Water storage inside the body gives the cactus more control over limited water resources.
Image source: Unknown


Canyon Live Oak. Leaves have small spines around their margins. The spines increase the leave's Surface Area / Volume. This effect can help the leaf more quickly dump heat to passing, cooler air.
Image source: Unknown


Does shape influence the surface area-to-volume ratio?

Surface area-to-volume ratio = the total surface area of an object divided by the total volume of the object.

The surface-area-to-volume ratio is an important operational feature for systems involved in exchanges from one object to another. The higher the surface-area-to-volume ratio, the faster and more effiecient the exchange. Often, exchange systems in biology take on a "branching" shape. For example the branching shape of roots, or the branching shape of lung air passages. Vons and Fry's Electronics stores increase the surface area to volume ratio by increasing the number of cash registers, making the exchange of merchandise and money faster and more efficient.

Volume = 8x8x1 = 64 cubic units

Surface Area = 2(8x8) + 4(8x1) = 160 square units

Surface Area/Volume = 160/64 = 2.5

Volume = 5x8x1 + 6x4x1 = 64 cubic units

Surface Area = 64x2 + 70 = 198

Surface Area/Volume = 198/64 = 3.1

Image source: Pearson Education, Inc.

Motorcycle engine with "cooling fins" that substantially increase the engine's surface area-to-volume ratio.
Image source: Unknown


Coping with Extremely Cold Winters

Broadleaf winter-deciduous

maple trees

Vermont Maple forest during the fall season. This broadleaf forest has mild summers, extremely cold winters.
Image source: Unknown


maple leaves

When ice crystals form inside leaf cells, they destroy the integrity and operations of the cell -- killing the cell, and collectively, the whole leaf.

During the fall season in regions with icy winters, broadleaf trees shutdown chlorophyll production and withdraw sugars and nutrients from the leaf into the branch for safekeeping during freezing winters. Then the leaf falls off the tree.

The following spring, the tree produces new leaves, and the cycle repeats.

This behavior is rewarding because it reduces the loss of resources from the unavoidable death of leaves killed by ice.
Image source: Unknown

When cold winters are very long, and summers are very short

Broadleaf trees do not have enough growing time to repay the losses incurred from fallen leaves of the previous autumn.

Conifer evergreen - winter hardening

Boreal / conifer forest - pine and fir trees during winter. Longer, colder winters and shorter, cooler summers as compared to temperate broadleaf forests.

Conifer trees do not drop their needles in winter -- so they do not experience the kinds of annual resource losses that broadleaf trees do in this climate.
Image source: Unknown


Conifer evergreen needles harden against frost and remain active during freezing conditions. These needles have a very thick, resiny sap that resists freezing.
Image source: Unknown


Water-rich environments -- Tropical Forests

Tropical rain forest. Hot and bright sun all year. Rain most of the year - 100 inches or more. Nutrient poor soil.
Image source: Unknown


Dipteryx in the Peruvian rain forest. Massive shallow roots efficiently acquire nutrients from rapidly decomposing fallen leaves.
Image source: Unknown


Salty Environments

Coastal marsh. This marsh is flooded with seawater.
Image source: Unknown


Desert salina. Extremely high salt content in soil.
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Pickleweed (Salicornia), found in coastal marshes and in desert salinas. Pickleweed takes in salty water, diverts the salts to the tips where the salt concentrates. Eventually, the salt kills the tip, after which the tip breaks off, taking the salt with it.
Image source: Unknown


Salt grass (Distichlis) - found in coastal marshes and in desert salinas. Salt grass takes in salty water then excretes excess salt to the outside of its blades.
Image source: Unknown

Links for Enrichment and Further Learning


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