Study On The Photosynthetic Characteristics Of Peach Cultivars In Three Seasons

Photosynthesis provides energy for crops, and photosynthetic efficiency effects directly on the yield and quality of crops. In resent years, with the development of portable photosynthesis system and chlorophyll fluorometer, increasingly attention was put on breeding and identification for promising cultivars. Numerous factors influence photosynthesis, P, is affected by environmental(radiation, temperature, water and nutrient availability, etc.) as well as genetic varibables(total area, orientation toward the radiation flux, anatomical structure, Chl contet, ribulose-l,5-bisphosphate carboxylase/ oxygenase activity of the leaves, etc.). In some species P_n varies among cultivars which may be due to higher tolerance of some cultivars to environmental stress and sonsequently to the higher P_n under poorer conditions. There were many researches about the photosynthetic characters of different cultivars, but little study on the comparison of different cultivars at the whole growth stages. This article studied the photo-ecological and chlorofluorescence characteristics of nine peach cultivars in spring, summer and autumn. The results showed that:(1) The P_n, G_s, T_r, AQY and CE of peach were highest in spring, then followed with autumn and summer. The LCP of peach gradually decreased from spring to autumn, between 54.7～91.9μmol.m^-2·s^-1 in spring and 12.4～48.2μmol·m^-2·s^-1 in autumn. The LSP was in a range of 900-1400μmol·m^-2·s^-1 in each season, with no significant trend change. Among nine peach cultivars, 'Yuhualu' had higher diurnal integral value and maximum value of P_n in all the seasons, showing distinctly high photosynthetic ability and resistance to photoinhibition. Contrarily, the photosynthetice abilities of 'Okubo'and 'Sunagowase' were weaker in three seasons. Moreover, gas exchange parameters of all the cultivars were also analysed according to their relationships. The P_n of most hybrids were similar with their parents in spring, but significantly higher than parents in summer and autumn, showing potential photosynthetic abilities at middle and late stage.(2) Differed with significant decrease of gas exchange parameters in summer, most of peach cultivars had no obviously decline in F_v/F_m, F_v/F_o, F_v'/F_m',φPSⅡand qp. expect 'Zaoxiangyu'in summer, 'Okubo'and 'Sunagowase'in autumn. Non-photochemical fluorescence quenching (NPQ) of most cultivars increased in the period of summer, especially 'Baihua'和'Hakkobi', whose increasing range are respectively 112% and 67%, showing that NPQ protecting the photosynthetic apparatus by non-photochemical pathway. (3) The diurnal variation tape of P_n in peach was two-peak tape in three seasons, and the degree of midday depression of photosynthesis in spring was relatively lower than in summer and in autumn. The diurnal integral value of Pn was different significantly both among seasons and cultivars. The diurnal integral value of P_n in spring is highest, then followed autumn and summer. Among nine cultivars, 'Yuhualu' had higher value of diurnal integral and diurnal peak of P_n, showing distinctly high photosynthetic ability during the growth cycle, while 'Sunagnwase' had the lowest diurnal integral of Pn with significant decline in summer and autumn. The relational grade analysis of grey system theory was also used to analyze the relational gray coefficient and grade on leaf net photosynthetic rate of peach. The factor which seriously influenced leaf P_n of peach was C_a in spring, T_a in summer, and PFD in autumn.(4) the content of chla, chlb and carotenoid in leaves of peach in summer were significantly higher than in spring and in autumn, while chla/b was lower than in other two seasons because of the rapid increasement of chlb in summer. Correlation analysis showed that there was a positive relation existed between photosynthetic pigment contents and P_n in spring and autumn, and a significantly opposite relation in summer. Besides, chl.a/b was non-significantly positively related to P_n in three seasons. Photosynthetic pigment contents were significantly different among peach cultivars. There are higher photosynthetic pigment contents in leaves of 'Zaoxiangyu', 'Baixianglu', and 'Chunlei' in all the three seasons but lower in 'Sunagnwase' and 'Okubo' in autumn. Although Anthocyanin content was both increased in leaves, 'Sunagowase' and 'Chunlei' owned different photosynthetice abilities on account of different Chlorophyll contents.