Abstract:

【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.

Key words: Nitraria tangutorum, soil moisture, gas exchange, morphological characteristic, photosymthesis, semi-arid area