Transcript The Atmospheric Environment

The Atmospheric Environment
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

Climate
Light
 Temperature
 Moisture
 Wind
 Relative Humidity

Light Absorption
Vital to life
 Affected by mowing, leaf area
 Affected by leaf angle
 Influenced by surroundings

 clouds
 buildings
 trees
 Clippings
- light exclusion!
The Fate of Solar Radiation
Reflection
Absorption (heat)
Reradiation
Absorption
(chemical)
Transmission
Light Quality
Ultraviolet
Infrared
Visible Spectrum
400 nm
700 nm
Light Quality
Photosynthesis
has two peaks in
the visible range
Ultraviolet
Infrared
Visible Spectrum
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
Light Intensity
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

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
Photosynthetic Light Curve
Inhibition
Carbohydrate Storage
Maintenance
0
Compensation Point
Low
Medium
Light Level
Full Sun
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

Photosynthetic Light Curve
Shade-adapted
Sun-adapted
0
Low
Medium
Light Level
Full Sun
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

Shade Increases Disease
Thinner leaves less resistant
 Sun inhibits spore germination
 Higher humidity increases spore
germination

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

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

Best Species for Shade Tolerance

Cool Season
 Tall
fescue
 Fine fescues
 Bentgrass

Warm Season
 St. Augustine
 Zoysia
 Centipede
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

Temperature
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
Evaporation
 Reradiation
 Conduction
 Convection
 Advection

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).

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.

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
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 aren’t replaced as fast.

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
Heat Hardiness of CS Turfgrasses
Tall Fescue, Creeping Bent
Kentucky Bluegrass
Fine Fescues
Perennial Ryegrass
Annual Ryegrass
Highest
Lowest
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
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
Wind
Evaporative cooling
 Increases ET, evapotranspiration
 Deposits soil, sand, snow, seeds, pollen,
spores
 Wind-blown sand as abrasive
 Enhances CO2 exchange. How?

The Atmosphere: approx. 360 CO2 molecules
per 1 million total gas molecules
Stomates on a Leaf Surface
Epidermal cells
Wind keeps CO2 replenished
Stomate Opening
Stomatal
Cavity
“Dead” Air Becomes Depleted of CO2
Epidermal cells
Stomate Opening
Stomatal
Cavity
Sources/Forms of Water
Precipitation
 Irrigation
 Dew and guttation
 Gaseous - Relative Humidity

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

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

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
