The Atmospheric Environment
Atmospheric Environment
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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
Climate
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Light
Temperature
Moisture
Wind
Relative Humidity
Light Absorption
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Vital to life
Affected by mowing, leaf area
Affected by leaf angle
Influenced by surroundings
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clouds
buildings
trees
Clippings - light exclusion!
Light Duration Affects Form
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Short days (spring and fall) affect:
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increased density
greater tillering/stolons/rhizomes
shorter leaves
more leaves
smaller shoots
more prostrate growth habit
Opposite occurs in long days of summer
Light Intensity
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Seasonal
Latitude
Time of day
Atmospheric screening
Topography
Sufficient Light Intensity is required to sustain adequate photosynthesis
and thus growth.
All turfgrasses prefer to grow in full sunlight.
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
High light, where photosynthesis is high enough to produce extra carbohydrate
that can be stored
Temperature and other stresses can affect the ability of a turf to effectively utilize
higher light levels
Physiological Responses to Low Light
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Higher chlorophyll content
Lower respiration
Lower compensation point
Reduced carbohydrate reserves
Lower demand for water, nutrients
Reduced heat, cold, drought, wear tolerance
Developmental Responses to Low Light
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Reduced growth
Thinner leaves
Reduced shoot density; Reduced tillering
Longer, more erect leaves
Leaves are more succulent (less substance)
Longer internodes
Slower establishment
Shade Increases Disease
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Thinner leaves less resistant
Sun inhibits spore germination
Higher humidity
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
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Shade moderates air temperatures
Shade is associated with increased humidity, which may increase heat load, diseases
Shade from Trees:
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Tree roots compete for water and nutrients. Where are the tree roots?
Allelopathy - some tree roots exude specific chemicals which interfere with turf growth
Deciduous trees present extra problem in fall when leaves are shed. This can lead to extreme
light exclusion.
Best Species for Shade Tolerance
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Cool Season
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Warm Season
Tall fescue
Fine fescues
Bentgrass
St. Augustinegrass
Zoysiagrass
Centipedegrass
Managing for Shade
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Thin tree canopy. Also increase wind, reduce humidity
Raise cutting height
Reduce N fertility
Irrigate deeply, infrequently
Control traffic
Fungicides to control disease
Fertilize tree roots separately
Temperature
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The most important environmental factor affecting the adaptation of turfgrasses to a particular
geographic region.
Growth generally confined to > 40o, < 105o F
Temperatures fluctuate depending on the amount of energy received from the sun
Heat can be Transferred from One Environmental Component to
Another
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Evaporation
Reradiation
Conduction
Convection
Advection
Turf Modifies Temperatures
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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).
Evaporation requires large input of energy, which is “used up” by converting
water from liquid to gas
Turf Response to Temperature
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Minimum
Maximum
Optimum
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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
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50-65 o for cool season
75-85 o for warm season
Temperature Effects on Roots
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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 aren’t replaced as fast.
High Temperature Stress
(often associated with drought stress)
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Indirect:
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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
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Direct:
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High temps can kill turf. CS at 100-130o F
Crown, young leaf, apical meristem are more tolerant than older tissue
Heat Hardiness of Cool Season Turfgrasses
Tall Fescue, Creeping Bent
Kentucky Bluegrass
Fine Fescues
Perennial Ryegrass
Annual Ryegrass
Low Temperature Stress
Direct stress: when the liquid inside the cell freezes. Cells may rupture, proteins
denature. Depends on level of tissue hydration
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Prevent by correcting compacted soils
Avoid excessive fall nitrogen
 Maintain adequate potassium, phosphorus
 Minimize thatch accumulation
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Cold Tolerance of WS Turfgrasses
Zoysiagrass, Buffalograss
Bermudagrass
Bahiagrass
Centipedegrass
St. Augustinegrass
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?
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When soils are warm and microbial respiration is high
During flooding or ponding
When surface is sealed, diffusion is low
Wind
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Evaporative cooling
Increases ET, evapotranspiration
Enhances CO2 exchange. How?
Wind-blown sand as abrasive
Deposits soil, sand, snow, seeds, pollen, spores
Sources/Forms of Water
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Precipitation
Irrigation
Dew and guttation
Gaseous - Relative Humidity
Dew and Guttation
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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
Guttation
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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
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.
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Controls the amount of dew
Partly controls evaporative cooling