| Acid rain is one of the most serious pollution what the world facing today,and the pollution is very wide-ranging.Many regions of South China is one of the world's three major acid rain polluted area.The acid rain and acid deposition caused many hazards on forest development. Affecting plant growth is the main hazard of acid rain on Woody Plants.Therefore,the study of acid rain stress on photosynthesis of plants is very important to understanding the changes of forest succession and the restoration work in acid rain regions.A controlled experiment was conducted in Zhejiang Forestry College experimental base, making the simulated acid rain concentration in accordance with the control(pH5.6),mild(pH4.5), moderate(pH3.5),and severe(pH2.5),according to local average monthly rainfall to determine the spray volume.The selected materials were Schima superba,Iiexintegra Thunb,Parakmeria Latungensis,Quercus glauca,Lithocarpus glabra,two years old young seedlings,belonging to subtropical broad-leaved species in Zhejiang.The materials were planted in the pots which were 22cm in diameter and 27cm high between May 2006,using photosynthesis measured system LI-6400 analyzed the photosynthesis and transpiration,and using PAM-2100 analyzed the relevant indicators of chlorophyll fluorescence in different rain conditions.By studying the effects of simulated acid rain on physiological characteristics of photosynthesis, the results showed that:the LCP and Rd of S.superba and P.Latungensis in the severe stress of acid rain significantly increased;the LCP of I.Thunb and Q.glauca in severe acid rain stress significantly increased;all the photosynthetic indicators of L.glabra under acid rain stress t didn't change significantly.The daily average net photosynthetic rate of S.superba and I.Thunb decreased with the reduction of rainfall pH value decreases;the daily average net photosynthetic rate of Q.glauca and L.glabra only decreased under severe stress,but increased in other acid rain stress;the daily average net photosynthetic rate of P.Latungensis was highest in mild acid rain stress and lowest in severe,the other treatments had the approximate daily average net photosynthetic rate.By studying the effects of simulated acid rain on water physiological characteristics,the results showed that:the daily average net transpiration rate of S.superb and I.Thunb decreased with the reduction of rainfall pH value gradually;the daily average net transpiration rates of P.Latungensis in moderate and severe acid rain stress were higher than that in control and mild;Q.glauca and L. glabra had the approximate daily average net transpiration rates in all treatment,the lowest daily average net transpiration rate of Q.glauca appeared in moderate and the lowest of beech and oak-day deal with the transpiration rate is similar to beech daily transpiration rate and the lowest of L.glabra appeared in level in severe.The daily average water use efficiency of S.superba and i. Thunb decreased with the reduction of rainfall pH value gradually,and Q.glauca and L.glabra's were approximately,P.Latungensis had lower value of daily average water use efficiency in moderate and severe.Compared with the control,Q.glauca and L.glabra had the more little change of daily average water use efficiency than S.superba and I.Thunb.By studying the effects of simulated acid rain on chlorophyll fluorescence characteristics,the results showed that:compared with the control,the ETR values of S.superb were lower in all acid rain treatment;the Fv/Fo values of I.Thunb were lower,and the ETR values had the significant reduction in moderate and severe,and severe acid rain caused a significant reduction on the Yield values and increase on q_N in severe.Compared with the control,mild and severe acid rain stress caused the significant increase on the Fv/Fm and Fv/Fo values of Q.glauca,and severe acid rain stress caused a significant increase on q_N and a significant reduction on ETR;moderate and severe acid rain stress caused the significant increase on Fv/Fo,q_N and Yield of L.glabra,and there were a significant reduction in severe acid rain stress on its ETR.The chlorophyll fluorescence characteristics of P.Latungensis under the acid rain stress were in the relatively stable compared with the control.By studying the effects of simulated acid rain on chlorophyll fluorescence characteristics,the results showed that:in different treatment,the seedling's maximum values of seasonal net photosynthetic rate had emerged in summer,it means that the growth ability of the species are strongest in summer.The seasonal net photosynthetic rates of S.superba,I.Thunb and P. Latungensis were reduced with the reduction of rainfall pH value,but the values of Q.glauea and L. glabra were close between different treatment.The change of seasonal transpiration rate was like the photosynthetic rate.The maximum transpiration rate of seedlings appeared in the summer.For the WUE,the lowest values of seedlings had emerged in summer and decreased with the reduction of the pH value. In general,this paper:(1)studied the photosynthetic response characteristics of 5 species seedlings under the acid rain stress,it was found that L.glabra had the stronger adaptability of photosynthetic characteristics to acid rain stress than other species;(2)studied the water characteristics of 5 species seedlings under the acid rain stress,it was found that Q.glauca and L. glabra had the stronger adaptability of water characteristics to acid rain stress than other species; (3)studied the chlorophyll fluorescence characteristics of 5 species seedlings under the acid rain stress,it was found that Q.glauca and L.glabra had the stronger adaptability of chlorophyll fluorescence characteristics to acid rain stress than S.superba and I.Thunb,and P.Latungensis has the moderate adaptability of chlorophyll fluorescence characteristics;(4)studied the seasonal photosynthetic characteristics of 5 species seedlings under the acid rain stress,it was found that the influence of acid rain on the seasonal photosynthetic characteristics of Q.glauca and L.glabra was less than other species.The stronger adaptability to acid rain stress of Quercus glauca and L. glabra will be helpful for these two species to occupy an advantageous positions in the community succession,and the weaker adaptability to acid rain stress would make S.superba and I.Thunb Schima exit the succession process earlier,and P.Latungensis will have a stable position in community succession because of its moderate adaptability to acid rain.
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