Abstract:We explored the response mechanism of photosynthetic physiological parameters of wild Ziziphus jujuba var. spinosa to soil drought under the natural condition in the area of central and southern Shandong Province, and the quantitative relationship between the change process, mechanism and soil moisture under different water gradients. This paper studied wild Z. jujuba var. spinosa seedlings of 2 years old, and by artificial water supply and natural water consumption to simulate the soil drought under natural condition, studied the response process and mechanism of photosynthesis and fluorescence parameters of wild Z. jujuba var. spinosa leaves to the soil moisture (RWC). The results showed the following. (1) The gas exchange parameters in leaves of wild Z. jujuba var. spinosa which is the net photosynthetic rate (Pn), transpiration rate (Tr) and water use efficiency (WUE) were increased firstly and then decreased with the increase in soil water content. When the RWC <38.5%, the net photosynthetic rate (Pn) and the stomatal limitation (Ls) were both decreased, while, the intercellular CO2 concentration (Ci) was increased, which indicated that the decline of the photosynthetic rate of the leaves was mainly caused by nonstomatal limitation. When RWC = 38.5%-65.1%, the net photosynthetic rate (Pn) was decreased, the intercellular CO2 concentration (Ci) and stomatal conductance (Gs) were both decreased, and the photosynthetic rate of the leaves was also decreased in leaves of Z. jujuba var. spinosa at stomatal limitation stage. Therefore, the decline of the photosynthetic rate of wild Z. jujuba var. spinosa is about RWC=38.5% from the stomatal limit to the non stomatal limit. (2) The soil water content in leaves of wild jujube leaves with high photosynthetic productivity was 46.0%-80.5% by threshold simulation of Pn and WUE, and that of higher water use efficiency was 56.3%-73.9%. (3) In the process of soil drought (RWC range of 29.9%-86.5%) , the maximum fluorescence (Fm), the maximum photochemical efficiency of PSⅡ (Fv/Fm), and the PSⅡ actual photochemical efficiency (ΦPSⅡ) gradually decreased, the initial fluorescence (Fo) was significantly increased, the photochemical quenching (qP) was increased first and then decreased, the Nonphotochemical quenching (NPQ) was exhibited higher values with the excess or low of the soil moisture (RWC> 83.7%; RWC <38.5%), which showed that the heat dissipation of Z. jujuba var. spinosa was increased. The results showed that the parameters of gas exchange and chlorophyll fluorescence in leaves of wild Z. jujuba var. spinosa have obvious threshold response to soil moisture, and the RWC was about 38.5% at the threshold point. When RWC <38.5%, the photosynthetic rate of the leaves changed from stomatal limitation to nonstomatal limitation, the PSⅡof wild Z. jujuba var. spinosa was damaged, the electron transport was blocked and the photosynthetic mechanism was destroyed.