Study On Drought Resistance Of Three Cool-Season Turfgrasses

This paper studied the germination characteristics of perennial ryegrass"Accent",creeping bentgrass"Kromi",kentucky bluegrass"Kentucky"under the osmotic stress of polyethylene glycol 6000(PEG-6000), to evaluate the seed drought resistance in the germination stage. Using the single factor design, pot experiment was conducted to study the growth,morphological changes,physiological responsibilities of these three turfgrasses under the continuous drought stress. The relationships between the indexes under the irrigation and drought stress were analysed and a comprehensive evaluation on physiological indexes of three grasses was tried to provide the theoretical basis of water-saving irrigation in turf, and offer a reference index of evaluation of germplasm characteristics and breeding for forage. The results were as following:1 Germination test1.1 With the increase of the osmotic stress, the germination energies decreased. Perennial ryegrass and kentucky bluegrass were sensitive to the osmotic stress.1.2 The germination percentages of three turfgrasses decreased. The relationships between germination percentage and stress intensity were significant(p<0.01),the correlation coefficients were 0.962,0.913,0.929 respectively in perennial ryegrass,creeping bentgrass,kentucky bluegrass. The creeping bentgrass was easily affected by the osmotic stress, from the aspects of germination percentage and relative germination percentage.1.3 The growths of root and shoot of seedlings were inhibited to some extent. The relative root length and shoot length of seedlings both decreased under the increase of the osmotic stress. The relationships between stress intensity and relative root length,relative shoot length were significant(p<0.05). The changes of root-shoot ratio were different, creeping bentgrass was easily affected by the osmotic stress during the whole stress.2 Pot experiment2.1 The soil water content declined because of the soil evaporation and turfgrass transpiration. The turf qualities of three turfgrasses declined with the continuous drought stress, and their sensitivities to drought stress were different.2.2 The relative water content (RWC)decreased , leaf relative plasmalemma permeability(RPP)increased. The correlations between RWC and soil water content of three grasses were positive(p<0.01), the correlations coefficients were 0.988,0.980,0.975 respectively in perennial ryegrass,creeping bentgrass,kentucky bluegrass. The correlations between RWC and soil water content of three grasses were negative (p<0.01), the correlation coefficients were-0.921,-0.804,-0.932 respectively in perennial ryegrass,creeping bentgrass,kentucky bluegrass.2.3 The chlorophyll (Chl) content increased and then decreased after it peaked. The correlations between the Chl content and soil water content were negative(p<0.01) in perennial ryegrass,kentucky bluegrass, the correlation coefficients were―0.783,―0.716, but there was no correlation in creeping bentgrass.2.4 During the early period of drought stress, the proline (Pro) contents had no differences between the drought treatment and control. But Pro contents increased in the later period. The correlations between Pro content and soil water content were negative(p<0.01) in three turfgrasses, the correlation coefficients were -0.864,-0.875,-0.883 respectively in perennial ryegrass,creeping bentgrass,kentucky bluegrass.2.5 The activities of antioxidant enzymes had different changes. Superoxide dismutase(SOD) decreased after it peaked, with a negative correlation to soil water content. The correlation coefficients were -0.521,-0.775,-0.693 respectively in perennial ryegrass,creeping bentgrass,kentucky bluegrass. There were no correlations between the changes of peroxidase (POD) and soil water content in three grasses. There was no correlation between catalase(CAT) and soil water content in pernnial ryegrass. But there were correlations in creeping bentgrass,kentucky bluegrass, the correlation coefficients were 0.616,-0.680 respectively. The malondialdehyde(MDA) content fluctuated in the early period and then increased fast. The correlations between the MDA content and soil water content were all negative in turfgrasses, the correlation coefficients were -0.679,-0.736,-0.788 respectively in perennial ryegrass,creeping bentgrass,kentucky bluegrass.2.6 Applying the method of grey correlative degree analysis to comprehensively evaluate the grasses, the correlation of soil water content and 8 physiological indexes was analysed. The result showed that the sequences of index sensitivity to soil water content were: RWC>CAT>Chl>POD>SOD>MDA>Pro>RPPIn conclusion, the germination percentage,relative germination percentage and the root-shoot ratio could be used to reflect the sensitivity of seed to drought during the germination stage. The relative water content (RWC) could be used to reflect the sensitivity of turfgrass to the soil drought during the seedling stage.