Abstract: In recent years, it has been found that Quercus aliena var. acuteserrata mature forests in Baotianman Mountains in southwestern Henan Province in China are difficult to regenerate. This study aims to explore the reasons why Q. aliena could not well regenerate by investigating the effects of different light environments on photosynthetic characters and nonstructural carbohydrate (NSC) of Q. aliena seedlings, and to discuss the impact of sunfleck on Q. aliena regeneration. In this study, sunfleck was simulated by opening shading apparatus at noon every day. Five treatments were set up: control (CK, natural sunlight) and four shading treatments including shade by 80% with opening one hour at noon (T80-1), shade by 80% (T80), shade by 98% sunshine with opening one hour at noon (T98-1) and shade of 98% sunshine (T98). Dry matter yield, NSC of Q. aliena seedlings, gas exchanges in photosynthetically active radiation (PAR) under 1500 μmol·m^-2·s^-1, photosynthesisPAR curves, diurnal variation of photosynthesis and chlorophyll fluorescence parameters of the leaves were measured. The dry matter yield and total NSC content of Q. aliena seedlings in shaded treatments were significantly lower than those of CK. The NSC content of seedlings under simulated sunfleck treatments was significantly higher than that of the seedlings with corresponding only shading treatments. Serious shading treatment (T98) resulted in higher death rate of seedlings. Different light environments had significant effects on photosynthetic capacity of Q. aliena seedlings. The net photosynthetic rates (P_n) of T80, T98-1 and T98 were significantly lower than CK under high PAR because of nonstomatal limitation in the shading treated seedlings. The efficiency of photochemical reaction of T98 was the lowest among all treatments. Q. aliena seedlings showed the ability of shade tolerance to some degree, such as lower light compensation point and dark respiration rate in shaded treatments, and T98 had higher P_n than T98-1. In summary, Q. aliena seedlings had difficulty to maintain the balance of carbon and to survive in seriously shading environment. However, sunfleck relieved the negative influences of carbon reserves of Q. aliena seedlings in shading environment, and had significant effects on building up high photosynthetic capacity of seedlings under high light conditions.

Key words: precipitation, altitude, deuterium excess, water temperature, hydrogen and oxygen stable isotopes