The Atmospheric Environment

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

Climate n Light n Temperature n Moisture n Wind n Relative Humidity

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

The Fate of Solar Radiation Reradiation Reflection Absorption (heat) Transmission Absorption (chemical)

Light Quality Visible Spectrum Infrared Ultra- violet 400 nm 700 nm

Light Quality Visible Spectrum Infrared Ultra- violet Photosynthesis has two peaks in the visible range

Light Duration Affects Form of Cool Season Grasses n Short days (spring and fall) affect: u increased density u greater tillering/stolons/rhizomes u shorter leaves u more leaves u smaller shoots u more prostrate growth habit n Opposite occurs in long days of summer

Light Intensity n Seasonal n Latitude n Time of day n Atmospheric screening n 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: n 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. n 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: n 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 Photosynthesis Rate Light Level 0 LowMediumFull Sun Carbohydrate Storage Maintenance Compensation Point Inhibition

Physiological Responses to Low Light n Higher chlorophyll content n Lower respiration n Lower compensation point n Reduced carbohydrate reserves n Lower demand for water, nutrients n Reduced heat, cold, drought, wear tolerance

Photosynthetic Light Curve Photosynthesis Rate Light Level 0 LowMediumFull Sun Shade-adapted Sun-adapted

Developmental Responses to Low Light n Reduced growth n Thinner leaves n Reduced shoot density; Reduced tillering n Longer, more erect leaves n Leaves are more succulent (less substance) n Longer internodes n Slower establishment

Shade Increases Disease n Thinner leaves less resistant n Sun inhibits spore germination n Higher humidity increases spore germination

Shade is not just Reduced Light n 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 n Shade moderates air temperatures n Shade is associated with increased humidity, which may increase heat load, diseases

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

Best Species for Shade Tolerance n Cool Season u Tall fescue u Fine fescues u Bentgrass n Warm Season u St. Augustine u Zoysia u Centipede

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

Temperature n The most important environmental factor affecting the adaptation of turfgrasses to a particular geographic region. n Growth generally confined to > 40 o, 40 o, < 105 o F n Temperatures fluctuate depending on the amount of energy received from the sun

Heat can be Transferred from One Environmental Component to Another n Evaporation n Reradiation n Conduction n Convection n Advection

Turf Modifies Temperatures n Temperature extremes much less with turf surface than with bare soil, paving n Turf absorbs a substantial amount of energy n 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 n 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 n Where does the heat come from to evaporate the water? From the turfgrass plant and surroundings.

Turf Response to Temperature n Minimum n Maximum n Optimum u o for cool season shoot growth u o for warm season shoot growth n Root growth can continue as long as soil temperatures are favorable u o for cool season u o for warm season

Temperature Effects on Roots n Optimum temperatures produce white, long, multi-branched roots n Sub-optimal temperatures produce white, shorter, slower growing, less branched roots n 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) n Indirect: u rapid turnover of roots, resulting in loss of root system u decrease in shoot growth, perhaps due to reduction in photosynthesis, carbohydrates. May lead to summer dormancy n Direct: u High temps can kill turf. u 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 n Direct stress: when the liquid inside the cell freezes. Cells may rupture, proteins denature. Depends on level of tissue hydration u Prevent by correcting compacted soils u Avoid excessive fall nitrogen u Maintain adequate potassium, phosphorus u Minimize thatch accumulation

Aerial Components n CO 2 and O 2 are important in the plant and in the soil. Low levels of CO 2 in the plant will limit photosynthesis. Low levels of O 2 in the soil limit root respiration and thus root function. When does soil O 2 become a problem? u When soils are warm and microbial respiration is high u During flooding or ponding u When surface is sealed, diffusion is low

Wind n Evaporative cooling n Increases ET, evapotranspiration n Deposits soil, sand, snow, seeds, pollen, spores n Wind-blown sand as abrasive n Enhances CO 2 exchange. How?

The Atmosphere: approx. 360 CO 2 molecules per 1 million total gas molecules

Stomates on a Leaf Surface

Stomate Opening Stomatal Cavity Epidermal cells Wind keeps CO 2 replenished

Stomate Opening Stomatal Cavity Epidermal cells “Dead” Air Becomes Depleted of CO 2

Sources/Forms of Water n Precipitation n Irrigation n Dew and guttation n Gaseous - Relative Humidity

Dew and Guttation n Dew is condensation caused by differences in temperature between air and a surface. How does this happen in turf? n 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 n Occurs at night, shortly after fertilizing with soluble N fertilizers and with frequent irrigation n Liquid contains sugars, salts, amino acids, a perfect growth medium for pathogens n Guttation is removed to reduce disease and to improve mowing quality, reduce clippings from clumping

Relative Humidity n 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. n Controls the amount of dew n Partly controls evaporative cooling