Comparative Research On Adaptability Of The Ornamental Hawthorn

The hawthorn(Crataegus L.) belongs to the hawthorn department rose family (Rosaceae), it is regarded highly in application in landscaping for its good ornamental value.The experiment intended to set about from observing the phenology and the growth rhythm of introduction ornamental hawthorn, analysised their ecological characteristics in primary, in order to providing the theory basis for cultivation technique; the semi-lethal temperature of the ornamental hawthorn was measured by electrical conductivity method, 6 physiological indexes of the ornamental hawthorn ( the relative electric conductivity, content of chlorophy II , relative water content, the content of proline, MDA and SOD activity of their leaves ) were determined after high temperature treatment to synthetically evaluated their tolerance to high temperature treatment combing with the field observation ; the photosynthetic parameters in leaves of the ornamental hawthorn were determined under field conditions,which will be of great help to understanding of their adaptability to the environment, then will put forward as a basis for scientific cultivation and landscape application of the ornamental hawthorn.The main results were shown as follows:1. The phenology of Crataegus laevigata'Paul's Scarlet'are earlier than that of Crataegus laevigata'Crimson Cloud', the branth biomass in the first year was also longer than that of Crataegus laevigata'Crimson Cloud'.2. The relative electric conductivity of the excised-leaves of 10 species of hawthorn trees was measured by electrical conductivity method with a series of high temperature treatment, the semi-lethal temperature was gotten by seeking the point of inflexion on the curve, which accorded with Logistic equation. The results indicated that the heat tolerance of 10 species of hawthorn trees from strong to weak was Crataegus altaica(52.73℃) >Crataegus phaenopyrum(51.64℃) >Crataegus ambigua(50.59℃) >Crataegus laevigata'Crimson Cloud'(50.23℃) > Crataegus lavallei(49.91℃) > Crataegus moroenensis'Toba'(49.54℃) > Crataegus viridis'Winter King'(49.51℃) > Crataegus mollis'Downy'(48.20℃) > Crataegus laevigata'Paul's Scarlet'(47.46℃) > Crataegus crus-galli'Inermis'(47.42℃).3. The results of the leaf physiological changes showed that: there was comparatively obvious change happened in every physiological index after high temperature treatment, compared with normal temperature. Among them, the relative electric conductivity, the content of proline, MDA and SOD activity increased, the content of chlorophy a/b irregularly changed while relative water content decreased. There appeared some correlation between all the indexes.4. According to the clustering analysis of physiological indexes, 10 ornamental hawthorn species could be divided into 3 heat resistance classes: Crataegus moroenensis'Toba', C. mollis'Downy'and C. altaica into the first class ( high resistance); C. phaenopyrum and C. laevigata'crimson Cloud'into the second class (moderate resistance); and C. lavallei, C. laevigata'Paul's Scarlet', C. viridis'WinterKing', C. crus-galli'Inermis'and C. ambigua into third class (sensitive to heat stress).5. The gas exchange and chlorophy II fluorescence parameters in leaves of 16 ornamenta hawthorn species. The results showed that there were significant differences (p<0.01) in the net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), water use efficiency (WUE), intrinsic water use efficiency (WUE_i) among sixteen hawthorn species. For the chlorophy II fluorescence parameters, the differences in the initial fluorescence (F₀) was not significant at p<0.05 but the differences in maximal flurescence (F_m), potential efficiency of primary conversion of light energy of PSII (F_v/F_m), maximal fluorescence in light adaptation (F'm), quantum yield of PSII electron transport (ΦPSII), photochemical quenching coefficient (qp), non-photochemical quenching coefficient (NPQ) were significant at p<0.01.6. Correlation analysis among photosynthetic parameters showed that : there were significantly positive correlations between P_n and T_r , T_r and G_s, F_v/F_m and F'_v/F'_m or NPQ,P_n andΦPSII or q_p(p<0.01). However, there were significant negative correlations between Pn and F'_v/F'_m or NPQ, qp and F_v/F_m or NPQ(p <0.01).7. According to the clustering analysis of photosynthetic parameters,10 ornamental hawthorn could be divided into 4 classes: C. lavallei, C. crus-galli'Inermis', C. laevigata'Paul's Scarlet'and C. ambigua belonged to the first class (sensitive to heat stress); C.laevigata'crimson Cloud', C.mollis'Downy', C.phaenopyrum and C.viridis'WinterKing'belonged to the second class (moderate resistance); Crataegus moroenensis'Toba'belonged to the third class and C. altaica belonged to the fourth class ( high resistance).