This study tests the diurnal variations of water status, leaf gas exchanges and chlorophyll fluorescence in Pistacia vera L. (P. vera L.) and Pistacia atlantica Desf. (P. atlantica Desf.) seedlings. At 40% of field capacity, diurnal variations in water uptake, relative water content (RWC) were estimated every hour between 5:00 am and 7:00 pm. The daily course of light, temperature, photosynthesis (A), stomatal conductance (gs), transpiration rate (E), intrinsic water use efficiency (A/gs), mesophyll efficiency (A/Ci), internal CO₂ concentration (Ci) and chlorophyll fluorescence were measured every 3 h from 05:30 am to 7:30 pm in irrigated and stressed seedlings of the two studied species. The results showed a significant variation in all surveyed parameters over diurnal cycle. The stressed seedlings of P. atlantica exhibited considerably higher RWC, water uptake, A, gs, E, A/gs and A/Ci over diurnal cycles compared to P. vera stressed seedlings. In contrast, P. vera was more sensitive to water stress and excess light and temperature over the diurnal cycle. The midday stomatal conductance and photosynthesis decrease was more likely the result of low RWC caused by high transpiration rates, stomatal closture and photoinhibition. Photoinhibition is a protective mechanism of PSII, rather than a result of photo-damage of photosynthetic apparatus. P. atlantica revealed an important physiological feature that is maintaining photosynthesis at midday compared to P. vera. This might be due to internal regulation through several mechanisms mainly better osmotic adjustment, photoprotective mechanisms of PSII.

本研究测试了Pistacia vera L. ( P. vera L.) 和Pistacia atlantica Desf的水分状况、叶气交换和叶绿素荧光的昼夜变化。( P. atlantica Desf.) 幼苗。在田间持水量的 40% 下，每天上午 5:00 至下午 7:00 之间估计吸水量、相对含水量 (RWC) 的昼夜变化。日光、温度、光合作用（A）、气孔导度（gs）、蒸腾速率（E）、内在水分利用效率（A/gs）、叶肉效率（A/Ci）、内部CO ₂从上午 05:30 到下午 7:30，每 3 小时测量一次在两个研究物种的灌溉和胁迫幼苗中的浓度 (Ci) 和叶绿素荧光。结果表明，所有调查参数在昼夜循环中都有显着变化。与P. vera受胁迫的幼苗相比，受胁迫的P. atlantica幼苗在昼夜循环中表现出相当高的 RWC、吸水量、A、gs、E、A/gs 和 A/Ci 。相比之下，P. vera在昼夜循环中对水分胁迫以及过多的光和温度更敏感。中午气孔导度和光合作用下降更可能是由高蒸腾速率、气孔关闭和光抑制引起的低RWC的结果。光抑制是PSII的一种保护机制，而不是光合器官光损伤的结果。与P. vera相比，P . atlantica揭示了一个重要的生理特征，即在中午维持光合作用。这可能是由于通过几种机制的内部调节，主要是更好的渗透调节，PSII 的光保护机制。