Plsc 213-environmental factors

Light

wavelengths absorbed at different stages in the atmosphere and canopy

how the atmosphere removes light

• absorbtion of UV be ozone

• scattering of blue light by atmospheric gases

• scattering of long wavelengths by atmospheric dust

• scattering of all wavelengths by water vapor (clouds)

vegetation absorbs ____ light and transmits ______ depending on _________:

• absorbs violet, blue and red light but strongly reflects green light

• primarily transmits green and far red ligh

• amount of light reaching ground varies with quantity and position of leaves

LAI 

LAI increases as you move from the top of the forest canopy to the ground

photosynthesis and light availability

photo and resp respond directly to variations in leaf temperature

• the availability of light directly influences the level of photo

• light affects leaf temperature

• vertical reduction of canopy is estimated using beers law

sun species

• adapted to living in high quality light environments

• higher rate of photosynthesis

• rapid growth

• rapid establishment on disturbed sites (pioneer species)

shade tolerant species

• genetically based adaptations to low light environments

• lower photo and respiration

• continued photo under reduced light

• slower growth requiring less energy

red and far red light in the canopy

• ratio of red to far-red radiation decreases through the canopy, affecting the patterns of growth and allocation of plants on forest floor

how does LAI get affected by leaves 

• leaf angles intercept light and affect amount of light that passes through the canopy

• perpendicular to sun: absorbs 1.0 unit of light energy

• 60 degree angle to sun: 0.5 units of light energy

• affected by seasonal changes. leaves who drop their leaves allow more light to be available on the forest floor

differences in red and far red light 

• far-red reaches more than red light, but stops growth. red light encourages growth and can break dormancy

what will heat affect

rate of photosynthesis and energy storage

C3 plants

produce 3 carbon compounds

C4 plants

• CAM plants

• produce 4 carbon compounds 

• more effective in water storage since stomata

  is only open in evening to conserve moisture

• take up CO2 at night and not during the day

evaporation

• loss of moisture from a surface

• energy is required to convert surface water to vapor, produces a cooling effect

• amound of water that evaporates is dependent on the difference in vapor pressure between the surface and surrounding air, can also be influenced by the surface material itself

conduction

• transfer of heat between solid objects

• depends on the degree of contact, difference in temp between objects and resistance to heat transfer

convection

• heat transfer between fluids and solid objects

• occurs rapidly

thermal radiation

emission of long wave radiation

Latent heat

energy released during a phase change (ex. liquid to vapor)

sensible heat

heat energy stored in a substance as a result of increase in temp

thermal balance

heat transfer gains and losses

why is water important?

• life on earth is because of the unique properties of water

• water is essential medium for biochemical processes

• closely related to thermal balance

• absorbs light

water uptake through a plant:

• uptake based on differenc in water potential between soil and roots

• soil has high osmotic pressure 

• root has low, water will move in 

how to release water through stomata:

relative humidity of the atmosphere must be lower to create a gradient for water to move out 

hydrologic cycle

major pathways that affect water balance 

precipitation

rain, snow or fog. 

loss of water from clouds 

infiltration

movement of moisture into the soil 

surface runoff

movement of moisture across soil surface

groundwater

storage of water belowground in aquifers

transpiration 

evaporation of water from leaves

light absorption in water

water absorbs light rapidly

• red is most rapidly absorbed

  • as light is absorbed, water is heated up and distributed vertically into 3 regions

Thermocline

region located between the epilimnion and hypolimnion 

water temp declines most rapidly dependent on solar radiation 

epilimnion 

warm, low-density water

Top layer

hypolimnion

cold, high-density water

bottom layer 

how does seasonal changes affect water temp

changes in the vertical depths

in temperate zones water may experience a mixing of layers

effects of canopy on water temp

reduced vegetation allows more radiation than if there were a canopy