Plants 2 Flashcards
Plant issues in cold climates
Acclimation and freezing
Desiccation in the winter
Water supply during winter
Is there an advantage to being an evergreen?
Mechanical problems
Acclimation
A reversible change in the morphology or physiology of an organism in response to environmental change
For plants, they must become tolerant to temperatures
How do plants acclimate or acquire freezing resistance
The hormone abscisic acid (ABA) plays a role
ABA is photoactive and controls permeability of membranes to water
This controlling of water prevents intracellular ice formation
Frost cracks
Sudden temperature changes
Often at branch stubs, wounds
Water in wood and bark freeze and cause rapid expansion and contraction and damaged wood does not contract at the same rate
Desiccation in winter
Leaf stomata remain closed throughout most of winter, but diffusion of water vapor through the cuticle is significant and accelerated at low atmospheric humidity and high winds
Leaf resistances to diffusion provided by
Stomata
Waxy cuticle covering the leaf
Boundary layer
Effect of win on desiccation
Reduces humid boundary layer from around leaf, increasing the rate of transpiration
Cool the leaf and maintains temp equilibrium between leaf and air
Net effect of wind is
To reduce water loss
Water supply during winter
Xylem movement in plant is a passive process that relies on-
Cohesion of water
Capillary action in xylem tubes
Evapotranspiration of water from leaves
How does freezing in the xylem of conifers happen without cavitation
Water moving in xylem of conifers must pass through border pits located at ends of each conducting cell
Stretch across border pit is a membrane with thick central portion called the torus
Water normally moves freely around the torus
What happens to lead to the freezing that occurs in the xylem of conifers
Unequal tension or pressure distribution on either side of the torus, it closes off the border pit.
Is there an advantage to being an evergreen
Midwinter photosynthesis in norther conifers is not common
The photosynthetic process is not coupled to any of the metabolic processes controlling acclimation and freezing resistance
Therefore conifers benefit conifers benefit from extended photosynthetic season, not a continuous one
Purpose of bark in aspen
15 percent of total photosynthetic surface area, contributes substantially to the annual carb gain of the tree
Wintergreen leaves
Survive winter without withering
Mechanical problems
Heavy snow loads, blowing ice particles, even browsing activity of mammals pose problems for plants in winter-
Snow is extremely abrasive
May have strong influence on distribution of plant communities and development of plant growth form
