Lec 7 - Environmental Constraints Flashcards
abiotic environmental constraints
Plant distributions are often limited by physiological
tolerance to environmental conditions.
Climate envelopes (plant hardiness zones)
The location of
environmental conditions under which a species or
variety of plant can successfully survive and grow.”
Limiting factors of climate envelopes
Minimum winter temperatures, length of the frost-free
period, summer rainfall, maximum temperatures,
snow cover, January rainfall and maximum wind speed
Environmental tolerance
“The ability of an
organism to endure unfavourable environmental
conditions.”
Cold tolerance classification:
- Chilling sensitive (injury below 10-15 C)
- Freezing sensitive (injury below 0 C)
- Frost tolerant
Adaptations for cold:
- Acclimation
- Dwarfing
- Leaf characteristics
Heat injury
Primary effects of heat are on photosynthesis
Photosynthesis slowed / stopped as chloroplasts
damaged by temps >45-50 C
-Also tied with water limitation
Plants cool by:
-Radiative cooling (Emission of long-wave radiation)
-Convective cooling (Flowing air carries away heat)
-Evaporative cooling (Transpirational cooling)
-Diaheliotropism vs paraheliotropism (Sun tracking,
orient leaves to maximize or minimize sun exposure)
Coping by adjusting life history
Slow growth, go dormant, reproduce, change
photosynthetic strategy, go through life cycle quickly…
Wind damage:
- Windthrow
- abrasion by winborne soil particles
- dessication by wind
- Flagging (death of upwind tissues)
Adaptations to resist wind
Dwarfing or cushion growth (Krummholtz)
Salinity injury from:
-Water stress, plants must expend more energy to pull
water from a solute rich medium (due to osmosis).
-If solute concentrations are too high, plants will be
unable to pull water from the soil.
-Direct toxic effects of some ions on cells.
Salt-tolerant plants cope by:
Ability to divert, compartmentalize, or dispose of
potentially harmful ions so they don’t buildup in the
wrong place.
Lower rate of sodium and chloride transport to leaves
NOx SOx air pollution
Impacts stomatal behaviour, increasing water loss.
Acid rain
Acid deposition causes direct injury to the leaf surface
Lowers soil pH (acidifies soils)
As soils become more acidic, toxic substances can be
released from soil minerals (otherwise non-soluble).
O3 air pollution
Damages leaves, reduces photosynthesis, slows growth
