| Tall fescue is one of the most widely used cold-season turf grasses in China at present. The optimum growth temperature of tall fescue of shoot is 15-24℃and of root is 10-18℃. So it is difficult to survive heat and drought stress in summer in the transition zone in the Yangtze River area. The leaf of tall fescue turned yellow and turf quality decreased for nitrogen deficiency in summer. The experiment studied the effects and the regulation mechanism of nitrogen and ascorbic acid synergies on tall fescue so as to obtain appropriate application method of AsA and the appropriate combination of N and ASA for improving heat resistance of tall fescue turf grass. The results showed that:1. Under the heat stress of 40/35℃(day / night 12 h, respectively), water content, the ratio of green leaves and biomass of tall fescue declined rapidly. It showedplants' heat resistance was poor. After the application of ascorbic acid, the tiller weight and the ratio of green leaves improved. Treatment of sprayed with the 20mmol/L AsA were relatively better than of 10mmol/L and 30mmol/L. It improved the chlorophyll and carotenoid contents and the antioxidant enzymes (SOD, POD, CAT) activity and improved the AsA and GSH content, reduced the MDA and proline production and also improved the lawn heat resistance. And the concentration of 30mmol/L resulted in poisoning, burning spot on leaves and reducing the turf quality.2. Under heat stress, high nitrogen treatment aggravated stress injury. As a result, the plant dry weight decreased, tiller died, moisture content, green leaf number and pigment content decreased, and most plants died after eight days stress of heat and high N. It showed that high-temperature High-nitrogen double aggravated the stress of the metabolic rate, when in anti-oxidation system can not remove toxic substances at the plant caused the deaths. The treatment applied with AsA significantly increased the contents of chlorophyll and carotenoid, the activity of SOD, CAT and POD, soluble protein content, while decreased the contents of proline and MDA. AsA treatment also increased the water content, dry weight, green leaf ratio and tillers. Thus it improved the heat tolerance, postponed the senescence of tall fescue plants, which helped tall fescue to oversummer safely.3. During the resumption of growth, AsA can ease the injury of on the tall fescue after short-term high temperature under 5mmol/L of nitrogen level application. Tall fescue of 5mmol/L nitrogen treatment has a higher biomass, the ratio of green leaves (%), water content and plant root activity, strong antioxidant activity, soluble protein, free amino acid and soluble sugar content than of 0mmol/L and 10mmol/L of nitrogen level application. It showed that ascorbic acid and nitrogen coordination can remove reactive oxygen species effectively, and reduce the lipid peroxidation, improved the lawn heat resistance and the turf quality.4. compared with no spraying AsA, treatments of spraying frequency of 1 time / 1week, 1/2 weeks and 1/3 weeks of ascorbic acid with 5 mmol/L N level, all improved the biomass, tiller number, the ratio of green leaves and the survival rate of the plant, also improved the plant pigment content, activity, soluble protein content, such as lower membrane permeability. And the best treatment was spraying, then was 1/2 weeks spraying.
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