An analysis of photosynthetic parameters among Schima superba provenances
木荷种源间光合作用参数分析

Schima superba, a subtropical evergreen broad-leaved tree species, plays an important role in biological fireproofing and timber production in China. Previous studies focused mainly on the cultivation technique, fire forest belt construction and physiological ecology characteristic of S. superba. Photosynthetic parameters can be used to reflect tree growth characters. Most studies about photosynthesis of the S. superba focused on daily variation, relationship between photosynthesis and environment factors, photosynthesis rate and parameters of light response curve. Exponential function, rectangular hyperbola model, parabolic function and non-rectangular hyperbola model have been widely used to estimate parameters of light response curve. However, the maximum photosynthesis rates estimated by these models with data of light response curve were much larger than the measured values, and the light saturation points based on these models were much smaller. Moreover, these models can not model the phenomena that the photosynthesis rate decreased with increase of light intensity when light intensity was beyond light saturation points. The errors in photosynthesis rates and parameters estimation by these models of light response curve should be paid attention to. Especially, the errors caused by these models of light response curve will be amplified when the parameters of light response curve are used to the big scale models.. Fortunately, Modified rectangular hyperbola model overcomes these faults, and can model plant photosynthesis data in different light environments. It is very important for forestation to select good S. superba provenances according to provenance variation rules because S. superba has a wide natural distribution, and rich species variations. For S. superba, however, most parameters of light response curve were only estimated by exponential function, rectangular hyperbola model, parabolic function and non-rectangular hyperbola model which had much faults, and there was no available information about assessing different S. superba provenances based on the photosynthetic parameters such as maximum net photosynthetic rate, light compensation point and light saturation point. Therefore, we carried out a experiments to measure daily photosynthesis variation and light response curve of different S. superb provenances. The three provenances of S. superb were Kaiping in Guangdong province, Taiping in Anhui province and Yongfeng in Jiangxi province, respectively. The variables were measured using Li-6400 (LI-COR, Inc, Lincoln, NE, USA) from 9:00 to 16:00 on 10 to 13 October, 2010. Each measurement had three to five three replications. Based on modified rectangular hyperbola model, we calculated maximum net photosynthetic rate, light compensation point and light saturation point of S. superb from three provenances with three different latitudes. The results showed that the three provenances of S. superb had significant differences in photosynt