中文摘要：

美国山核桃（ Carya illinoensis）又名长山核桃、薄壳山核桃，原产于美国和墨西哥北部，是重要的高效生态经济型干果树种之一（ Lombardini et al．，2009）。我国引种美国山核桃已有百余年的历史，迄今已在20多个省（区、市）有小面积栽培分布。与中国的山核桃相比，美国山核桃具有果实个大、出仁率高、取仁容易、产量高等特点，且果实中的氨基酸含量比油橄榄高，还含有丰富的维生素B1和维生素B2（洪丹丹，2007）。

英文摘要：

In this study,a field experiment was conducted to compare photosynthetic physiological characteristics and the chlorophyll fluorescence parameters in leaves among five Carya illinoensis varieties, including Farley, Colby, Shoshoni,Cheyenne and Mandan. The results showed that there were significant （P〈0. 05） or highly significant （P〈0. 01）differences in minimal fluorescence （Fo）,maximum fluorescence （Fm）,PSⅡ potential activity （Fv/Fo）and non-photochemical quenching （NPQ） among the five varieties. The Fo and Fm of Shoshoni were higher than that of the other cultivars. The PSⅡ primary energy conversion efficiency （Fv/Fm） and PSⅡ potential activity （Fv/Fo） of Mandan were higher than those of the others,while the value of NPQ was lower. The light compensation point （LCP）of Mandan was significantly lower than that of the other varieties,indicating that it had a strong ability of using low light. Mandan and Shoshoni had higher maximum net photosynthetic rate （Amax）and relative chlorophyll content （SPAD）. Results of the correlation analysis showed that there were significant positive correlations between Fv and Fv/Fm,Amax and SPAD. A significantly negative correlation was found between NPQ and Fv/Fo.