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Linze jujube (Zizyphus jujuba Mill. var. inermis (Bunge) Rehd.) is a unique native selection with high-quality fruits. Photosynthetic capacity was evaluated under high temperature and irradiation using CO, exchange and chlorophyll fluorescence parameters. The diurnal course of net photosynthetic rate (P-n) was bimodal. The first peak occurred around 10:00 from late June to August. The second peak occurred around 17:00 during late June to late July with high temperature and intense sunlight, but around 16:00 in late August with lower temperature and irradiation. A clear midday depression of P. lasted from 12:00 to 16:00 from late June to late July, but it was less clear in late August. The light compensation point and light saturation point of P-n,P- were 28 and 1000 mu mol m(-2) s(-1), respectively, and the CO2 compensation point and CO2 saturation point of P-n were 64.3 and 677.5 mu mol mol(-1), respectively in late July. Under the conditions of high temperature (T-a > 40 degrees C) and irradiation (PFD > 2000 mu mol mol(-1)), photochemical efficiency of PS II (F-v/F-m) changed little between 0.78 and 0.84 all day, without photochemical damage. It was concluded that under the conditions of high temperature and irradiation, the midday reduction of P-n should be mainly attributed to stomatal conductance, which mainly resulted from the increase in vapor pressure deficit. (c) 2004 Elsevier B.V. All rights reserved.