Cover Story
TREES
AND
TURFS
By Larry Tankersley, Extension Forester, University of Tennessee Department of Forestry, Wildlife and Fisheries and Tom Samples, Ph.D., Turfgrass Science and Management, University of Tennessee Department of Plant Sciences
T
rees and turfgrasses share the same basic requirements in order to live. Both capture energy from sunlight in order to produce carbon-containing substances that are used immediately to support growth, or can be stored in reserve. Photosynthesis, the combination of carbon, hydrogen and oxygen from carbon dioxide and water in the presence of light results in the formation of glucose and other sugars. Atmospheric carbon dioxide is also the source of carbon in amino acids, proteins, starch and cell walls. Trees and turfgrasses have vascular systems (xylem and phloem), and rely on water for oxygen and hydrogen, and to move essential nutrients absorbed from the soil to leaves, and sugars produced in the leaves to roots. Fourteen mineral nutrients are essential for their survival and reproduction. Nitrogen, phosphorus, potassium, calcium, magnesium and sulfur are classified as macronutrients due to the quantity of each that is required. Due to the very small amount (usually 100 ppm or less) of each found in plant tissue, the remaining eight essential minerals, chlorine, iron, boron, manganese, zinc, copper, molybdenum and nickel, are referred to as micronutrients. Local air temperatures, annual rainfall amounts, and soil texture and fertility levels often determine if a particular species or variety of turfgrass or tree will thrive in the landscape. Although trees and turfgrasses growing in close proximity to each other must share resources (Table 1), this does not necessarily mean that they cannot co-exist. Successful management strategies assure that the fundamental requirements of both trees and turfgrasses are being met every year, even though growing conditions for each may be less than ideal.
Light Intensity, Quality and Duration. The rate at which
photosynthesis takes place within a tree or turfgrass usually increases with increasing light intensity. Light intensity is described as the amount of energy, or ‘packets’ of light referred to as photons, hitting the surface of a leaf over some time period. Light stimulates stomates to open. As a result, high light intensities are usually associated with high water transpiration rates. Only an estimated one to two percent of the solar radiation a turfgrass is receiving is absorbed and converted to chemical energy. Most of this absorbed energy is reradiated at much longer wavelengths, resulting in the release of heat. Turfgrass leaves with a horizontal
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orientation are more efficient absorbers of solar radiation compared to those growing more upright. The surfaces of turfgrass leaves may also reflect solar radiation. Dull and dry leaves are usually less reflective than glossy or wet leaves. Turfgrass leaves may also transmit solar radiation that may be absorbed by other leaves. In his book “Turfgrass Science and Culture” published in 1973, Michigan State University researcher and author, Dr. James Beard, reported that an estimated 20 to 25% of maintained turfs were receiving some level of shade from trees, shrubs or buildings. The canopy height of bermudagrass plants growing under low light intensities (less than 70 percent full sunlight) often increases by more than 100 percent compared to that of plants receiving full sunlight. Leaf elongation is often about 35 percent higher when cool-season turfgrasses are growing on sites with limited light intensity compared to the same species in full sun.
TABLE 1. Fundamental Requirements of Trees and Turfgrasses. S H A RE D RE S O U RCE S : Physical space, especially below ground Clean air, especially oxygen and carbon dioxide, free of toxins, above and below ground Sunlight, both enough (duration and intensity) and of the appropriate wavelengths (quality) Water, the right amount delivered on time Seventeen essential nutrients – carbon, hydrogen and oxygen from air and water, and 14 mineral nutrients supplied by the soil Minimum and maximum air and soil temperatures appropriate for growth and survival of both trees and turfgrasses
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