1. Animal, Plant & Soil Science E4-7 The Significance of Air in Plant Growth

2. Terms acid rain air air pollution atmosphere global warming humidity
particulates
pollutants
smog
water vapor

3. Objectives
1 Discuss the composition of air and how the components of air influence plant growth and development.
2 Explain the effects of humidity on plant growth.
3 Discuss the effects of air pollution on plant growth.

4. Interest Approach
Place a piece of marble or limestone in a beaker. A stone used for gravel mulch would work well. Pour enough vinegar into the beaker to cover the stone. Have students observe what happens. Vinegar has about the same pH as acid rain. Ask students what would happen if vinegar was sprayed on the leaves of a plant.

5. What is the composition of air and how do the components of air influence plant growth and development?
I. The Earth’s atmosphere is defined as the layer of gases surrounding the planet. The gases are held close to the Earth by gravity.

6. What is the composition of air and how do the components of air influence plant growth and development?
A. The Earth’s atmosphere contains roughly 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and about 0.002% of other gases, including neon, helium, methane, krypton, and hydrogen. There is also water vapor in varying amounts but usually around 1%. This mixture of gases is commonly known as air.

7. What is the composition of air and how do the components of air influence plant growth and development?
1. The atmosphere provides life on Earth with essential elements.
2. It protects organisms by absorbing harmful ultraviolet solar radiation.
3. The atmosphere is important in reducing temperature extremes between day and night.

8. What is the composition of air and how do the components of air influence plant growth and development?
4. Air has carbon dioxide and oxygen that are critical for photosynthesis and respiration.
a. Exchange of oxygen and carbon dioxide through stomata in the leaves keeps photosynthesis operating at peak efficiency.
b. The ability of air to move in and out of the soil is important in providing oxygen for healthy root growth. Root cells must have oxygen to undergo the vital life process of respiration. Root diseases surface when soil is saturated and oxygen is unavailable for cellular respiration. The cells sicken and die, and the roots become susceptible to soil-borne fungal and bacterial diseases.

9. What are the effects of humidity on plant growth?
II. The gaseous form of water is water vapor. Humidity, a term used to describe water vapor in the air, affects plant growth.

10. What are the effects of humidity on plant growth?
A. The growth rate of plants generally increases under conditions of high humidity. Lush, tropical forests exist, in part, because of frequent rain and high humidity. High humidity reduces water stress of a plant so that photosynthesis can function smoothly. If the humidity is low, the dryness of the air can put stress on the plant and cause wilting. This is especially true if soil moisture is inadequate.

11. What are the effects of humidity on plant growth?
B. High humidity can also contribute to plant disease. Smuts, rusts, mildew, anthracnose, and foliar diseases may develop in humid locations following wet weather. The causal agents include fungi and bacteria.

12. What are the effects of air pollution on plant growth?
III. Change to the quality of air to the extent that it affects the environment negatively is known as air pollution. Plants can be damaged from air pollution. The things that cause pollution are called pollutants.

13. What are the effects of air pollution on plant growth?
A. Particulates, small solid particles in the air, block the sun’s rays from reaching plants, thus slowing photosynthesis. Dust from the air that settles on leaf surfaces also reduces light intensity and rate of photosynthesis.

14. What are the effects of air pollution on plant growth?
B. Chemical pollutants come from many sources. Vehicle exhaust, gases from factories, and burning of plant materials contribute to pollution. The pollution might consist of sulfur oxides, nitrogen oxides, carbon monoxide, ozone, and unburned fragments of fuel. A mixture of these pollutants, often seen hovering over cities, is called smog. Pollutants can cause physical damage to plant tissues and weaken plant health.

15. What are the effects of air pollution on plant growth?
C. A serious pollution that threatens plants in and away from urban areas is acid rain. Acid rain is atmospheric moisture that has a low pH due to a presence of acids. One source of these acids is sulfur oxides emitted from fossil fuel plants and industry. Another source is nitrogen oxides, mainly from automobile exhaust. These compounds are converted in moist atmosphere into acids, such as sulfurous and nitrous acid. Winds carry these acids over a wide area through the atmosphere. The pH of rain that contains these acids has been measured at 4.2 and lower. The pH of non-polluted rain averages 5.6. Acid rain burns plant tissues and adversely affects the intake of nutrients. It has been very damaging to forests in some locations.

16. What are the effects of air pollution on plant growth?
D. Carbon dioxide, methane, and fluorocarbons contribute to global warming. Global warming is the increase in the temperatures of near-surface air and oceans. The burning of fossil fuels contributes to the addition of these pollutants to the atmosphere. Global warming can alter the climates to which plants are adapted and lead to changes in agricultural production.

17. REVIEW
1. What is the composition of air and how do the components of air influence plant growth and development?
2. What are the effects of humidity on plant growth?
3. What are the effects of air pollution on plant growth?