【目的】为预测干旱半干旱地区荒漠灌木对水资源紧缺现状的响应,分析了不同水分条件对白刺幼苗光合及形态特征的影响。【方法】以内蒙古乌兰布和沙区的白刺为试验材料,设置5个土壤水分梯度:CK、T1、T2、T3、T4(分别为田间持水量的100%、≥80%~100%、≥60%~80%、≥40%~60%、≥20%~40%),对其气体交换参数及各器官形态特征进行研究。【结果】与对照(CK)相比,水分含量降低到≥40%~60%和≥20%~40%(T3和T4)时,白刺的净光合速率日变化均存在下降的趋势,分别下降了42.16%和44.73%;在不同的水分处理下,白刺蒸腾速率与气孔导度密切相关,并且相关系数大于净光合速率与气孔导度的相关性;各水分处理下白刺水分利用效率的日均值大小顺序为:T2>T1>T3>CK>T4。T2处理下,白刺根、茎、叶各形态指标达到最大值,并且显著高于其他处理(P<0.05)。【结论】从白刺的光合特征角度看,在不同的水分处理下,白刺的净光合速率的日变化均呈双峰曲线,并在14:00左右净光合速率值最低,均存在光合“午休”现象。根据白刺净光合速率、胞间CO₂浓度以及气孔限制值的变化,在CK、T1和T2处理下白刺光合“午休”的原因主要是由气孔因素引起;在T3和T4处理下光合“午休”的原因主要是由非气孔因素引起。60%~80%的土壤含水量是适宜白刺生长的最佳水分条件。

【Objective】To study the effects of the photosynthesis and morphological characteristics of Nitraria tangutorum seedlings produced in Ulan Buh desert under different water conditions.【Method】 Gas exchange parameters and morphological characteristics were studied with five water treatments CK, T1, T2, T3 and T4 (100%, ≥80%-100%, ≥60%-80%, ≥40%-60% and ≥20%-40% of field capacity, respectively).【Result】With decreasing water content, the daily variation photosynthetic rate of N. tangutorum also decreased; the daily variation in the photosynthetic rate decreased by 42.16% and 44.73% when the water content decreased to ≥40%-60% and ≥20%-40%, respectively (T3 and T4). In addition, the transpiration rate and stomatal conductance of N. tangutorum were closely related, and the correlation coefficient was higher than that for the net photosynthetic rate. The daily mean value of the water use efficiency of N. tangutorum was T2>T1>T3>CK>T4. The root, stem, and leaf reached the maximum under the T2 treatment; it was significantly higher than those under other treatments (P < 0.05).【Conclusion】Under the five different water treatments, a diurnal change in the photosynthetic rate presented a “double peak” curve; in addition, a photosynthetic “lunch break” phenomenon was observed at two o’clock in the afternoon. According to the change in the net photosynthetic rate, the intercellular CO ₂ concentration and stomatal limitation value of N. tangutorum,showed that photosynthetic lunch break phenomenon was caused by stomatal factors under the CK, T1 and T2 treatments and non-stomatal limitation under the T3 and T4 treatments. A total of ≥60%-80% soil water content was identified as the best moisture condition for the growth ofN.tangutorum.