1. FACTORS AFFECTING PLANT GROWTH

3. MEASURING GROWTH Increase in fresh weight Increase in dry weight
Volume
Length
Height
Surface area

4. HOW PLANTS GROW Meristems Dicots Apical meristems – vegetative buds
shoot tips
axils of leaves
Cells divide/redivide by mitosis/cytokinesis
Cell division/elongation causes shoot growth
Similar meristematic cells at root tips

5. HOW PLANTS GROW Meristems (cont) Secondary growth in woody perennials
Increase in diameter
due to meristematic regions
vascular cambium
xylem to inside, phloem to outside
cork cambium
external to vascular cambium
produces cork in the bark layer

6. Plant Growth and Development
Photosynthesis
Respiration
Transpiration
The above 3 items drive plant growth

7. ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH
Light
Temperature
Water
Humidity
Gases
Nutrition
It is important to know how these factors affect
plant growth and development.
With a basic understanding of these factors, you
may be able manipulate plants to meet your needs.
By recognizing the role of these factors, you may be
better able to diagnose problems caused by
environmental stress.

8. ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH
Light
Sun’s radiation
not all reaches earth; atmosphere absorbs much
visible (and some invisible) rays pass, warming surface
reradiation warms atmosphere
Intensity
high in deserts; no clouds, dry air
low in cloudy, humid regions
earth tilted on axis; rays strike more directly in summer
day length varies during year due to tilt

9. ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH
PAR (Photosynthetically Active Radiation)
Plants absorb blue and red light. Blue light is mainly responsible for vegetative growth.
Red light when combined with blue light encourages flowering.

10. ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH
Light (cont)
Photoperiodism – response to varying length of light and dark
It was first believed that day length was the main factor affecting plant flowering. However, it was later found out that it was the length of darkness.

11. Plants are classified into 3 day length categories:
Short day length plants flower when they are exposed to less than 12 hr. sunlight (mums, X-mas cactus, poinsettias)
Long day plants flower when the day length exceeds 12 hours. This includes most summer flowering plants and vegetables.
Day neutral plants flower regardless of day length such as tomatoes, corn, cucumber, and strawberry.
Duration - Photoperiodism - Plant behavior in relation to day length
- long day plants - flower only if days are longer than same critical period - 12 hours Grains and clovers
- short day plants - flower only if days are shorter than a critical period soybeans.
- indeterminate - flower over a wide range of day lengths. Tomato, cotton, buckwheat
Some crops fail to flower in certain geographical areas
Chrysanthemums can be made to bloom by controlling photoperiod.

13. ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH
Temperature
high light intensity creates heat; sunburned
low temp injury associated with frosts
Low temperatures reduce energy use and increase sugar storage. Citrus is sweeter after cold weather.
Adverse temp. may cause stunted growth and poor quality. High temperatures cause bitter lettuce.

14. ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH
Water
most growing plants contain about 90% water
amount needed for growth varies with plant and light intensity
transpiration drives water uptake from soil
water pulled through xylem
exits via stomates
evapotranspiration - total loss of water from soil
loss from soil evaporation and plant transpiration

15. ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH
Gases
Nitrogen is most abundant
Oxygen and carbon dioxide are most important
plants use CO2 for photosynthesis; give off O2
plants use O2 for respiration; give off CO2
stomatal opening and closing related to CO2 levels
oxygen for respiration limited in waterlogged soils
increased CO2 levels in atmosphere associated with global warming
additional pollutants harm plants