Photosynthetic characteristics of linze jujube in conditions of high temperature and irradiation

Abstract

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 2 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 n 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 were 28 and 1000 μmol m −2 s −1, respectively, and the CO 2 compensation point and CO 2 saturation point of P n were 64.3 and 677.5 μmol mol −1, respectively in late July. Under the conditions of high temperature ( T a > 40 °C) and irradiation (PFD > 2000 μmol 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.