Temperature in plants Flashcards
Effects of temperature of enzyme function and membranes
- Photosynthetic rate drops 35-40C
- Plant tissue dies at about 46C
- Freezing temperatures varies greatly
- Most species do not photosynthesize when ambient temperature reaches freezing; exception scots pine begin photosynthesizing at 3-4C and continue until -7C
- Leaf temperatures are fairly constant across climates during growing season
- Difference in plants from boreal/temperate vs. tropical climates
Effects of cold stress
- Decreased membrane fluidity
- altered lipid concentration (membranes)
- slower metabolism
- ice in intercellular space
- cells shrink
Effects of heat stress
- Dehydration
- Withering leaves
- Yellowing: deterioration of chlorophyll
- “Sunburn”; happens as chlorophyll deteriorates, the red pigments become more visible
Heat exchange in plants
o Metabolism (gain) o Radiation (loss or gain) o Convection (loss or gain) o Evaporation (loss) o Conduction (loss or gain)
Evergreens vs. Deciduous
Evergreens:
- maintain leaves, possibility of photosynthesis
- compact, leathery leaves protect from heat loss
- grow in nutrient-poor areas, cannot afford to be deciduous
Deciduous
- lose leaves seasonally
- larger, flatter leaves maximize light absorption
Raunkier’s Life Forms
- classified based on first growth point o Phanerophytes (woody trees) – 25 cm above soil o Chamaephytes (woody bushes) – 25 or less cm above soil o Hemi-cryptophytes (low lying) – at or near surface o Cryptophyte (mostly below ground or under water) o Therophytes (survive winter as seeds only)
Raunkier’s Life Forms: Tropical
o Consistently warm and wet
o Trees dominate
Raunkier’s Life Forms: Subtropical
o Warm, but less wet
o Trees dominate, but more shrubs
Raunkier’s Life Forms: Temperate
o Variable temp and moisture
o Lower lying plants dominate, followed by those that maintain buds underground
Raunkier’s Life Forms: Arctic
o Cold, dry, short grow season
o Low-lying dominate
o Few annuals
o No trees
Raunkier’s Life Forms: Desert
o Hot during the day, cold at night and dry
o Annuals, trees
Typical arctic plants
o Dark leaves increase heat gain from sun through radiation
o Low compact growth that decreases exposure to wind (convection)
o Plants are ground-hugging to gain heat from conduction from solar heated ground
o Leaves orient perpendicular to sunlight to maximize benefit
o Antarctic plants – only 2 native species
Antarctic hair grass
Antarctic pearlwort
Non native: chickweed, yellow bog sedge (being brought in by visitors and scientists, mostly accidentally) – invasives
Typical desert plants
- Leaves orient parallel to sun to reduce heat gain
- High reflective leaves to reduce heat gain
- Open growth form and small leaves increases exposure to wind
- More upright structure to reduce conductive heat gain from ground
- Ability to manipulate microclimates
• Create a soil microclimate by providing shade and leaf litter
• Ex: 48 C in bare soil, 29 C in litter under small shrub, 27 C in soil under small shrub, 21C in littler under tall shrub, 23C in soil under tall shrub
More genetic adaptations to cold
- More sugars
- More unsaturated lipids in cellular membranes
- Small, waxy, evergreen leaves
- Rapid growth during short growing season
- Photosynthesis below freezing
- Pubescence (some plants have hair on leaves or stems that can function like insulation)
Genetic adaptations to heat
- Water storage
- Leaves with hairs (also a response to cold)
- Night flowering
- Deep, long root system
- No leaves (photosynthetic stems)
- Slow growth rate
