Careful water management is critical to growing quality creeping bentgrass during summer stress periods, especially in sand-based root zones. Many golf course superintendents in the mid-Atlantic region and elsewhere irrigate creeping bentgrass greens lightly and frequently (LF) or deeply and infrequently (DI). LF irrigation involves applying water before wilt is evident and maintaining soil moisture at or near field capacity (Fry and Huang, 2004). DI irrigation is defined as irrigating at the first sign of leaf wilt to replenish the root zone with water (Fry and Huang, 2004). DI irrigation generally is recommended for maintaining cool-season grasses in summer (Beard, 1973; Fry and Huang, 2004).
Carbohydrate metabolism in leaves and sheaths, including photosynthesis, respiration, and carbon translocation, are major physiological processes that form the basis of healthy plant function. Creeping bentgrass summer performance may be improved by maximizing carbohydrate production through photosynthesis, while minimizing carbohydrate consumption from respiration (Xu and Huang, 2000). TNC availability has been widely used as a physiological measure of stress tolerance because carbohydrates provide energy and solutes for osmotic adjustment. The major TNC found in grasses include water-soluble (i.e., glucose, fructose, sucrose) and storage (i.e., starch and fructan) sugars (Smith, 1972).
Understanding the many physiological factors affecting rooting is critical because roots can be a nutrient sink and obviously can contribute to overall plant health maintenance. Efficient carbon allocation to roots might increase the probability of plant survival during periods of drought stress (DaCosta and Huang, 2006a; Sisson, 1989). Several investigations have found that turfgrass plants subjected to drought stress accumulate more carbohydrates in leaves, stems, and roots when compared with well-watered plants (DaCosta and Huang, 2006a; Huang and Fu, 2000 and 2001; Huang and Gao, 2000). Soil drying reduces the proportion of newly photosynthesized carbon allocated to leaves, while increasing the proportion of carbon allocated to tall fescue (Festuca arundinaceae Schreb.) roots (Huang and Fu, 2000; Huang and Gao, 2000). This allocation of carbon to roots occurred to a greater extent in the more drought-tolerant tall fescue cultivars evaluated (Huang and Gao, 2000). Similarly, DaCosta and Huang (2006a) reported that newly photosynthesized carbon increased during the early phase of drought stress in creeping bentgrass roots, but not in leaves and stems.
We are not aware of any field studies that have investigated carbon metabolism in creeping bentgrass maintained as a putting green in response to summer irrigation practices. Therefore, the objectives of this field study were as follows: to quantify canopy net photosynthesis and whole respiration rates, and to quantify WSC, SC, and TNC levels in creeping bentgrass grown in a sand-based root zone in response to LF versus DI irrigation in the summer.
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