| Kentucky bluegrass is a kind of word-wide used cool-season turfgrass. There are rich Kentucky bluegrass germplasm resources in China, so many turfgrass researchers pay great attention to them. In this experiment non-stress treatment was made as control to study physiological and biochemical characteristic and photosynthetic physiological characteristic of 5 Kentucky bluegrass cultivars under drought and heat stress, the main results are shown as follows:1. The results of the experiment suggested that drought and heat stress caused soil water content, leaf water potential, leaf relative water content of 5 Kentucky bluegrasses to decline with stress time prolonging. But these 3 indexes changed differently due to different cultivars and treatment time. At the end of stress, these 3 indexes of 5 cultivars was lower than that of non-stress level. The soil water content of 5 Kentucky bluegrasses during stress period was lower than the level of non-stress time. Decline of soil water content for Impact and Bluechip was larger than that of the other 3 cultivars, which indicated that Falling amount of leaf water potential of Conni and Award was larger than tha of the other 3 cultivars, which shew that damage of two cultivars under stress was more serious than the other 3 cultivars. Thus, drought and heat stress caused water shortage of turfgrass. Leaf relative water content of 5 cultivars gradually decreased with soil water content of 5 cultivars decline under drought and heat stress. Moreover, The falling of leaf relative water content of Conni and Award was more significant than that of other cultivars according to change of the whole course, which indicated that drought and heat stress caused more serious damage to Conni and Award than the other 3 cultivars.2. Drought and heat stress lead to LW increase and TQ decline. At the end of stress, TQ of 5 cultivars was lower than that non-stress level, while LW of 5 cultivars was higher than non-stress level. In the whole stress course, falling for TQ of Conni and Award was more significant than the other 2 cultivars. So we may consider that drought and heat caused damage to turfgrass, exhibited LW increase and TQ decline. Furthermore, damage degree of Award and Conni was heavier than Bluechip, Impact, and Nuglade. 3. Drought and heat stress lead to two enzymes (SOD, CAT) activity of 5 cultivars fall differently.The changes of two enzymes (SOD, CAT) activity of 5 cultivars were different under drought and heat stress. Activity of SOD began to fall a bit at primary treatment period, and then raise, it started to fall at mid-last period of treatment. The trend of change had significant difference according to different cultivars. However, the change of CAT enzyme activity showed an unvariable decline trend, which was not constent with change of SOD enzyme. The results indicated that the SOD, CAT enzyme activities of Bluechip, Impact, Nuglade could maintain a high level, which meant that the 3 cultivars were suffered from less damage than the other 2 cultivars, morever, the 3 cultivars could resist drought and heat stress and had a certain drought and heat tolerance to some extent. With falling of enzymes (SOD, CAT) activity, lipid peroxidation producetion-MDA content and EL raised, even MDA content and El of 5 cultivars were higher than that of non-stress period. During the whole treatment, MDA content and EL of Conni and Award were higher than that of Bulechip, Impact, and Nuglade, which suggested that damage degree of Conni, and Award was larger than that of the other 3 cultivars.4. Drought and heat stress caused damage to photosynthetic system of 5 cultivars. Photosynthetic system indexes just like Pn, Tr, Chl, Gs, Ci, and Fv/Fm of 5 cultivars began to decline. The value of these 6 indexes was lower than that of non-stress level. All photosynthetic indexes had some differences according to different cultivars and different treamental time. Under drought and heat stress, the stress caused soil water content to decrease, which led to leaf relative water content decline again, shortage of water in cell of plant gave rise to stoma to close to different extent, and then led to Gs, Ci, Tr decline. With drought and heat stress period prolonged, the speed of Chl decomposed exceeded that of Chl composed, which caused Chl content to decline. Falling of Gs made CO2 content reduce, which led to carbone assimilative ability decrease. That is falling of photosynthetic ability and Pn, Fv/Fm. According to the whole stress course, falling of photosynthetic ability of Conni, Award were more significant than the other 3 cultivars, which indicated that drought and heat stress caused damage to photosyhthetic system of plant.5. In brief, the damage which Award, and Conni were suffered was more serious than that which Nuglade, Bluechip, and Impact were suffered in the whole stress course. So we might preliminary determine that Bluechip, Impact, and Nuglade among 5 tested cultivars had stronger ability to live through the summer at dry and hot regions (example: Zhangye city and so on). The 3 cultivars were suitable cultivars to be introduced and grown at these dry-hot regions. Morever, these comprehensive tested indexes would provide reliable scientific reference for screening high quality and tolerant drought and heat stress cultivars for the future.
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