Physiological mechanisms of creeping bentgrass (Agrostis palustris L.) tolerance to summer stress

Understanding creeping bentgrass (Agrostis palustris Huds) responses to summer stresses will help develop effective breeding and management programs to improve turf quality. The objectives of this study were to (1) examine seasonal physiological changes and variation of four cultivars in shoot growth; (2) examine mowing and irrigation effects on shoot and root growth; (3) investigate lipid peroxidation of cell membranes and carbohydrate status in relation to heat tolerance; and (4) to examine cytokinin (zeatin riboside, ZR) effects on heat tolerance. Two field studies were conducted on a USGA-specification putting green in Manhattan, Kansas, during 1997 and 1998 to address objectives 1 and 2. Two growth chamber studies were conducted to address objectives 3 and 4.; Turf quality of 'L-93', 'Crenshaw', 'Providence', and 'Penncross' declined during summer, which could be related to decreases in canopy photosynthetic rate and increases in whole-plant respiration rate. Among four cultivars, Penncross had the lowest turf quality; L-93 had the highest; Providence and Crenshaw were intermediate but closer to L-93.; Decreasing mowing height from 4 mm to 3 mm significantly reduced turf quality and root growth of 'Penncross' and 'Crenshaw'. Low mowing decreases canopy photosynthetic rate but increases whole-plant respiration rate, which could lead to carbohydrate depletion, especially during summer months.; When two cultivars ('Penncross' and 'L-93') were subjected to heat stress in growth chambers, turf quality, concentrations of some carbohydrates, and activity of superoxide dismutase (SOD) and catalase (CAT) decreased, while root mortality, cell membrane permeability, and lipid peroxidation increased in both shoot and roots. These changes were greater for 'Penncross' than 'L-93'. Results suggested carbohydrate depletion and lipid peroxidation could contribute to heat injury.; Applications of 1 and 10 mumol ZR to the root zone soil during bentgrass exposure to high soil temperatures alone, or in combination with high air temperatures, increased turf quality, canopy photosynthetic rate, activity of antioxidant enzymes (SOD and CAT), ZR content, and likewise decreases in lipid peroxidation occurred cell membrane injury. The 10 mumol ZR was most effective in alleviating heat stress injury.