Abstract: With economic development， the type of acid rain pollution in China changed from the sulfuric acid to sulfuric acid and nitric acid complex， due to the increase of nitrogen content in the acid rain， which may lead to the change of terrestrial plant ecosystem. In this paper， Carya cathayensis was used as the experimental material to study the effect of simulated sulfuric acid rain （SAR）， nitric acid rain （NAR） and the mixed acid rain （MAR） on physiological characteristics in Carya cathayensis. In experimental design， in addition to three types of acid rain， three gradients of pH value as pH 2.5 （severe acid rain stress）， pH 4.0 （moderately acid rain stress）， pH 5.6 （acid rain control treatment） were also designed. The growth parameters， chlorophyll content and photosynthetic reaction parameters of Carya cathayensis under three pH values and three types of acid rain were experimentally determined. The experimental results showed that: under SAR， plant height， basal diameter of Carya cathayensis in pH 5.6 was higher than the other two gradients. In the NAR treatment， the growth performance showed as pH 5.6 <pH 2.5 <pH 4.0. In the MAR treatment， the stress on plant height was significantly higher than SAR and NAR. Under the same pH value， the stress effects on chlorophyll showed as NAR> MAR> SAR， and there are significant differences in chlorophyll content among different types of acid rain but not among different pH values in the same acid rain treatment. Three types of acid rain showed inhibitive effect on photosynthesis characteristics of Carya cathayensis， the net photosynthetic rate under pH 2.5 was less than pH 5.6. The apparent quantum efficiency （AQE）， maximum net photosynthetic rate （Pnmax）， light saturation point （LSP） was lower in MAR treatment than NAR. The results showed that NAR and MAR showed more complex influence on plant physiological characteristics of Carya cathayensis than SAR， the plant height and chlorophyll content in mixed acid rain treatment was greater than sulfuric acid rain.

Key words: Carya cathayensis, acid rain, stress, physiological characteristics