Studies On Photosynthetic Characteristics Of Different Cultivars And Affecting Factors Of Pear

In this paper, the net photosynthetic rate (Pn) and the diurnal variation curves of photosynthesis of five different types of pear cultivars were measured using the CIRAS-1 Portable Photosynthesis System. The photosynthesis characteristics under shading condition and of different types shoots were also studied. The results showd that:The Pn of leaves are difference among these different types of pear cultivars, the Pn of Qingxiang (sand pear cultivars) and Huangguan (sand pearxwhite pear) leaves are higher than that of Red-Barllet, and that of Xin-Yar li (white pear cultivars) and Kuerlexiang Ii (Xinjiang li cultivars) is in the middle of them. The water use efficiency (WUE) of Qingxiang and Xin-Yar li leaves is higher than that of Red-Barllet. The stomatal conductance (Gs) of Huangguan, Qingxiang and Kuerlexiang li leaves is higher than that of Red-Barllet. The intercellular CO2 concentration (Ci) of Kuerlexiang li leaves is the highest among these cultivars, and Ci of Qingxiang and Xin-Yar li is lower. The light compensation point (LCP) and CO2 compensation point (CCP) of different types of pear cultivars leaves are slightly lower, and there are no significant difference among these cultivars, however, the LSP and CSP are few higher; in addition, for Huangguan, the LSP is higher, and the CSP is lower. The carborylation efficiency of leaves are slightly different among different types of pear cultivars, however, the appearance quantum yield (AQY) of leaves are significantly different among these determined cultivars, and the AQY of Huangguan and Kuerlexiang li leaves is higher than that of Qingxiang and Xin-Yar li leaves. The diurnal variation curves of Pn among different types of pear cultivars are different, and there are two types, single-apex curve and anisomerous double-apex curve. The diurnal variation curves of Pn of Xin-Yar li and Huangguan present single-apex curves, and that of Qingxiang, Red-Barllet and Kuerlexiang li present anisomerous double-apex curves. The photosynthesis siesta is caused mostly by nonstomatal limitation in Qingxiang, Red-Barllet and Kuerlexiang li. The diurnal variation curves of transpiration rate(Tr) among these determined pear cultivars present single-apex curves. The diurnal variation curves of Ci present single-valley and double-valley curves, and that of Qingxiang and Huangguan present single-valley curves, and that of Red-Barllet, Kuerlexiang li and Xin-Yar li present double-apex valley curves. The diurnal variation curves of Gs present many types, that of WUE present single-apex curves and that of the stoma limit ratio present single-apex and double-apex curves, Qingxiang and Huangguan present single-apex curves and Red-Barllet, Kuerlexiang li and Xin-Yar li present double-apex curves.After shading the Pn of these two cultivars decease drastically, and the diurnal variation curves of Pn of these two cultivars change from single-apex curves to double-apex curves ; the photosynthesis siesta is caused mostly by nonstomatal limitation in Xizilu,however, mostly stomatal limitation in Cuiguan. The Gs , Ci, Ccp, Csp and chlorophyll contents of these determined cultivars leaves increase, however, the Tr, WUE, LSP, MDA contents, AQY, the value of chla/chlb n carborylation efficiency (CE) and dark respiration(Rd) of determined pear cultivars leaves decrease. The LCP of Cuiguan leaves increase slightly, however, that of Xizilii leaves decrease.The results of comparing fruit-bearing shoots with nutritive shoots indicated that, the Pn , Tr , Gs, Ci, AQY and Rd of leaves of fruit-bearing shoots are higher than that of nutritive shoots; the WUE of nutritive shoots is higher than that of fruit-bearing shoots; the LCP and LSP, CCP, CSP and CE of leaves are slightly different between nutritive shoots and fruit-bearing shoots. The results of comparing long fruit branches with middle fruit branches and fruit spur indicated the orders of different photosynthesis characteristics values from large to small in turn are that: for the Pn of leaves, fruit spur, middle fruit branches, long fruit branche...