The Atmospheric Environment

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The Atmospheric Environment
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Atmospheric Environment

• Macroenvironment - up to 5 ft above the ground,
  representative of the overall climate
• Microenvironment - immediate vicinity of the
  turfgrass plant, ranging from the canopy surface
  to the bottom of the rootzone

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Climate

• Light
• Temperature
• Moisture
• Wind
• Relative Humidity

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Light Absorption

• Vital to life
• Affected by mowing, leaf area
• Affected by leaf angle
• Influenced by surroundings
• clouds
• buildings
• trees
• Clippings - light exclusion!

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The Fate of Solar Radiation
Absorption (heat)
Reflection
Reradiation
Absorption (chemical)
Transmission
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Light Quality
Ultra- violet
Infrared
Visible Spectrum
400 nm 700 nm
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Light Quality
Photosynthesis has two peaks in the visible range
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Light Duration Affects Form of Cool Season Grasses

• Short days (spring and fall) affect
• increased density
• greater tillering/stolons/rhizomes
• shorter leaves
• more leaves
• smaller shoots
• more prostrate growth habit
• Opposite occurs in long days of summer

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Light Intensity

• Seasonal
• Latitude
• Time of day
• Atmospheric screening
• Topography

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Sufficient Light Intensity is required to sustain
adequate photosynthesis and thus growth. All
turfgrasses prefer to grow in full sunlight.
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Three Components of Photosynthesis

• Compensation point - where the light level is low
  and just adequate to produce enough
  photosynthesis to match respiration. The net
  gain of carbon is zero.
• Intermediate light levels produce enough
  carbohydrates to compensate for nighttime
  respiration, plus enough extra to support new
  growth and sustain tissue

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Three Components of Photosynthesis

• High light, where photosynthesis is high enough
  to produce extra carbohydrate that can be stored.
  Excessively high light may be damaging
• Temperature and other stresses can affect the
  ability of a turf to effectively utilize higher
  light levels

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Photosynthetic Light Curve
Inhibition
Photosynthesis Rate
Carbohydrate Storage
Maintenance
0
Compensation Point
Low Medium Full Sun
Light Level
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Physiological Responses to Low Light

• Higher chlorophyll content
• Lower respiration
• Lower compensation point
• Reduced carbohydrate reserves
• Lower demand for water, nutrients
• Reduced heat, cold, drought, wear tolerance

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Photosynthetic Light Curve
Sun-adapted
Shade-adapted
Photosynthesis Rate
0
Low Medium Full Sun
Light Level
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Developmental Responses to Low Light

• Reduced growth
• Thinner leaves
• Reduced shoot density Reduced tillering
• Longer, more erect leaves
• Leaves are more succulent (less substance)
• Longer internodes
• Slower establishment

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Shade Increases Disease

• Thinner leaves less resistant
• Sun inhibits spore germination
• Higher humidity increases spore germination

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Shade is not just Reduced Light

• Light quality can change as it passes through the
  tree canopy. The tree leaves remove the red
  and blue light components, leaving mainly the
  green, which is not effective in photosynthesis
• Shade moderates air temperatures
• Shade is associated with increased humidity,
  which may increase heat load, diseases

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Shade from Trees

• Tree roots compete for water and nutrients.
  Where are the tree roots?
• Deciduous trees present extra problem in fall
  when leaves are shed. This can lead to extreme
  light exclusion. How to handle?
• Allelopathy - some tree roots exude specific
  chemicals which interfere with turf growth

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Best Species for Shade Tolerance

• Cool Season
• Tall fescue
• Fine fescues
• Bentgrass

• Warm Season
• St. Augustine
• Zoysia
• Centipede

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Managing for Shade

• Thin tree canopy. Also increases wind, reduces
  humidity
• Raise cutting height
• Reduce N fertility
• Irrigate deeply, infrequently
• Control traffic
• Fungicides to control disease
• Fertilize tree roots separately

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Temperature

• The most important environmental factor affecting
  the adaptation of turfgrasses to a particular
  geographic region.
• Growth generally confined to 40o,
• Temperatures fluctuate depending on the amount of
  energy received from the sun

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Heat can be Transferred from One Environmental
Component to Another

• Evaporation
• Reradiation
• Conduction
• Convection
• Advection

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Turf Modifies Temperatures

• Temperature extremes much less with turf surface
  than with bare soil, paving
• Turf absorbs a substantial amount of energy
• Much of the energy is dissipated by one of the
  transfer processes. The most important is
  evapotranspiration (ET, total loss of water from
  turf and soil surface).

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Turf Modifies Temperatures

• Evaporation requires large input of energy, which
  is used up by converting water from liquid to
  gas. This is called the latent heat of
  evaporation
• Where does the heat come from to evaporate the
  water? From the turfgrass plant and
  surroundings.

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Turf Response to Temperature

• Minimum
• Maximum
• Optimum
• 60-75 o for cool season shoot growth
• 80-95 o for warm season shoot growth
• Root growth can continue as long as soil
  temperatures are favorable
• 50-65 o for cool season
• 75-85 o for warm season

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Temperature Effects on Roots

• Optimum temperatures produce white, long,
  multi-branched roots
• Sub-optimal temperatures produce white, shorter,
  slower growing, less branched roots
• Supra-optimal temperatures produce roots that
  become brown, spindly, mature rapidly, die
  faster, and arent replaced as fast.

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High Temperature Stress(often associated with
drought stress)

• Indirect
• rapid turnover of roots, resulting in loss of
  root system
• decrease in shoot growth, perhaps due to
  reduction in photosynthesis, carbohydrates. May
  lead to summer dormancy
• Direct
• High temps can kill turf.
• Crown, young leaf, apical meristem are more
  tolerant than older tissue

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Heat Hardiness of CS Turfgrasses

• Tall Fescue, Creeping Bent
• Kentucky Bluegrass
• Fine Fescues
• Perennial Ryegrass
• Annual Ryegrass

Highest Lowest
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Low Temperature Stress

• Direct stress when the liquid inside the cell
  freezes. Cells may rupture, proteins denature.
  Depends on level of tissue hydration
• Prevent by correcting compacted soils
• Avoid excessive fall nitrogen
• Maintain adequate potassium, phosphorus
• Minimize thatch accumulation

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Aerial Components

• CO2 and O2 are important in the plant and in the
  soil. Low levels of CO2 in the plant will limit
  photosynthesis. Low levels of O2 in the soil
  limit root respiration and thus root function.
  When does soil O2 become a problem?
• When soils are warm and microbial respiration is
  high
• During flooding or ponding
• When surface is sealed, diffusion is low

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Wind

• Evaporative cooling
• Increases ET, evapotranspiration
• Deposits soil, sand, snow, seeds, pollen, spores
• Wind-blown sand as abrasive
• Enhances CO2 exchange. How?

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The Atmosphere approx. 360 CO2 molecules per 1
million total gas molecules
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Stomates on a Leaf Surface
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Wind keeps CO2 replenished
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Dead Air Becomes Depleted of CO2
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Sources/Forms of Water

• Precipitation
• Irrigation
• Dew and guttation
• Gaseous - Relative Humidity

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Dew and Guttation

• Dew is condensation caused by differences in
  temperature between air and a surface. How does
  this happen in turf?
• Guttation occurs when the plant absorbs more
  water from the soil than it loses through the
  stomates. The excess is exuded through cut leaf
  ends or through special pores called hydathodes,
  at the leaf tips

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Guttation

• Occurs at night, shortly after fertilizing with
  soluble N fertilizers and with frequent
  irrigation
• Liquid contains sugars, salts, amino acids, a
  perfect growth medium for pathogens
• Guttation is removed to reduce disease and to
  improve mowing quality, reduce clippings from
  clumping

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Relative Humidity

• Can influence night temperature. High humidity
  reduces long wave reradiation, which keeps
  surfaces warmer. Desert turf cools off at night
  due to low humidity, permits CS turf to be grown
  in very hot climates.
• Controls the amount of dew
• Partly controls evaporative cooling