| Zhejiang which situates in subtropical monsoon zone is a strong economical province in China. There are many important economical tree species such as Carva cathayensis Sarg., Myrica rubra (Lour.) Sieb. et Zucc. and so on, meanwhile, also is timber industry province, but the raw materials of timber about 70 percent must be imported from other provinces, Outline of program for development the precious trees in Zhejiang was announced in june 2008, the Machilus pauhoi Kanehira would be greatly developed in Zhejiang. However, with the economical development, there is appeared region of acid rain major on Hangzhou, and the intensity, times and range of acid rain had been increased progressively in Zhejiang province in recent years, the effect of acid rain on the ecosystem and the economical development should not be neglected, whether the economical trees and precious trees would be growth under serious acid rain is a problem worthy to be dicussed.In this study, a pot experiment using two old seedlings of Carva cathayensis Sarg., Myrica rubra (Lour.) Sieb. et Zucc. and Machilus pauhoi Kanehira were performed with treatment of pH5.6(control), pH4.0 and pH2.5 simulated acid rain, in order to study the effect of different gradients of acid rain on the growth and photosynthetic of the three species, effect of different gradients of acid rain on photosynthetic physiology of three species under different seasons (spring, summer and autumn) and effect of different gradients of acid rain on growth and photosynthetic physiology of three species under different treatment times of acid rain(July 2007, July 2008 and July 2009).The effect of acid rain on the growth and photosynthetic physiology of the three species after two years treatment of acid rain, the results indicated that the chlorophyll content of three species were not significantly influenced by the acid rain. SAR(pH 4.0 and pH2.5) significantly increased the stomatal conductance(Gs), Net photosynthetic rate(Pn), maximum net photosynthetic rate(Amax), plant heigh and ground diameter of Carva cathayensis Sarg.,but the dark respiration rates(Rd) was noticeable decreased. SAR(pH4.0) has no significant effect on the Pn, intercellular CO2 concentration(Ci) and Gs of Myrica rubra(Lour.) Sieb. et Zucc., decreased the transpiration rate(Tr), Rd, light compensation point(LCP) and plant height, SAR(pH2.5) had lowed the Pn, Gs, Tr, Amax, Rd, LCP of Myrica rubra(Lour.) Sieb. et Zucc., but promoted the plant height. There were no significant changes on plant height, ground diameter, chlorophyll content and photosynthetic parameters of Machilus pauhoi Kanehira exposed SAR of pH4.0, while Machilus pauhoi Kanehira was exposed to the pH2.5, the Ci, Tr, Rd, LCP, Gs were significantly improved, but the Pn, Amax, apparent quantum efficiency(AQE) and plant height distinctly reduced.The diurnal variation of photosynthetic physiology of three species after three years acid rain treatment were studied, results showed:the diurnal of Pn of three species varied with double peak curves, they had the significant midday depression phenomenon, the Gs and water use efficiency(WUE) were lower at that time. Through regression analysis, the main factors of effect on the Pn was Gs and Ci under pH5.6 and pH4.0, while Gs was not the main factor that effect on the Pn of Myrica rubra(Lour.) Sieb. et Zucc. and Machilus pauhoi Kanehira under pH2.5.The photosynthetic physiology of three species in different growth seasons under different gradients acid rain were measured in 2009, the results showed: light saturation point(LSP) and AQE of Carva cathayensis Sarg. were not significant change by the SAR, while the LCP was improved, and Pn, WUE, chlorophyll content were reduced by the SAR in spring and summer. SAR had no significantly influenced on the LSP, LCP, AQE, Pn and chlorophyll content of Myrica rubra(Lour.) Sieb. et Zucc. in all seasons, but WUE was significantly decreased, and the Gs and Tr were improved by the acid rain in the summer and autumn. The effect of acid rain on the Machilus pauhoi Kanehira was differently in the different seasons, compared to the CK(pH5.6), LSP and LCP were significantly improved and AQE was significantly reduced by the acid rain in the spring, Pn was obviously decreased under SAR (pH2.5) in spring and autumn but no significant influence in summer.The growth and photosynthetic physiology of three species under different gradients of acid rain were measured after the one year, two years and three years treatment of acid rain, the results showed: The reaction model of three species under SAR was differently because of different treatment times. For the Carva cathayensis Sarg., Pn was significantly reduced in the first year, Gs and Pn were improved, Rd was decreased after two years treatment of the acid rain, Rd and Tr were increased, Pn and Gs was decreased after three years treatment. From three years study, the trend of growth under pH4.0 was from reducing to increasing, but under the pH2.5, the significantly promoted effect only appeared in the second year. For the Myrica rubra (Lour.) Sieb. et Zucc., SAR remarkably improved the Pn in the first year, but had no significant influence on the plant height and ground diameter, there were no significant influence on the Pn in the second year and the third year, while SAR (pH4.0) significantly lowered plant height and diameter in the second year, and had no significant influence in the third year, SAR(pH2.5) significantly increased the plant height in the second year and the third year. The effect of the acid rain on Machilus pauhoi Kanehira, there was no significant influence on the photosynthetic in the first year, and SAR (pH2.5) inhibited it with the prolonged treatment time, inhibitory effect had remission in the the third year, but there were some differently about effect of acid rain on the growth, promotion appeared on the first year, the second and third year both showed inhibition.In conclusion, these experiments'results indicated that:(1)Although there were some side effects on the photosynthetic of Carva cathayensis Sarg., the acid rain had promote growth of plant height and ground diameter, there may be exist some processes to resistant the side effects from acid rain, suggested that Carva cathayensis Sarg. had the ability to resistant the acid rain (2)Although acid rain of pH4.0 inhibit the plant height and ground diameter in the second year, Myrica rubra(Lour.) Sieb. et Zucc. had the high Pn under the treatment of acid rain, SAR (pH2.5) significantly promoted the plant height in the second and third year, this suggested the strong resistance to acid rain of Myrica rubra(Lour.) Sieb. et Zucc..(3)There was no significant influence on the photosynthetic of Machilus pauhoi Kanehira in the first, and SAR (pH2.5) inhibited it with the prolonged treatment time, inhibitory effect had remission in the third year, but there were some contradictions between growth and photosynthetic, growth was promoted appeared in the first year, the second and third year both showed inhibition. In view of acid rain in the Zhejiang province, Machilus pauhoi Kanehira can be carried out introduction in Zhejiang province,but where is the best area should be further more studies.
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