Abstract:

In order to explore the indices and comprehensive evaluation of sensitivity to acid rain,six seedlings of subtropical species,including Myrica rubra,Cinnamomum camphora,Schima superba,Liquidambar formosana,Pinus elliottii and Metasequoia glyptostroboides were taken as test materials and exposed to simulated acid rain (SAR) with different pH values (pH 3.5,pH 2.5,and local reservoir water of pH 50-54 as the control).Gas exchange parameters,the chlorophyll content,membrane penetration and malondialdehyde content(MDA)were determined after treated for four months.The results showed SAR at pH 35 was unlikely to cause significant damage on gas exchange parameters and cell membrane,while pH 25 treatment altered gas exchange parameters significantly,net photosynthetic rate (pn),stomata conductance(gs),transpiration rate(Tr)and water use efficiency(WUE)were significantly declined.Compared with the controls,the membrane penetration and MDA contents in the seedling leaves under pH 25 treatment were increased significantly.The characters of seedlings behaved variously in their susceptibility to acid rain,therefore it was essential to apply more than one index to give a comprehensive evaluation on stress resistant.Principal component analysis could transfer many correlating indices into several independent comprehensive indices with little original information lost.Based on the test results,seven correlated single indices which had very close relationship with the acidic tolerance characters,were transferred into two independent comprehensive,with contribution ratio of accumulative total of 88.064%.Then,according to acidic tolerance coefficients and standardization eigenvector of seven respective charcters of each variety,two comprehensive indices scores could be calculated.The comprehensive evaluation value of each seedling acidic tolerance (D value) could be decuced by weighting sum the subordinative values and weight coefficient of the two comprehensive indices scores.The acidic tolerance of six subtropical species could be distinguished by hierachical cluster analysis,and M.rubra and P.elliottii were the strongest tolerance,followed by C.camphora,L.formosana,S.superba,and M.glyptostroboides was the weakest.The evaluation results accorded with their behavior in the field,which suggested the method could give an objective and precise evaluation on the sensitivity to acid rain between different species of seedlings