Combined Effects Of Simulated Acid Rain And Al On Physiological And Ecological Characteristics Of Hydrangea Macrophylla

In south China,the frequency of acid rain is high,the acidified area of red soil is large,and the aluminum-rich degree is high.The purpose of the experiment was to reveal the mechanisms of acid rain and aluminium toxicity to plants and to provide a reference for soil remediation of Hydrangea in acid rain and aluminium-contaminated areas in the south.In this study,two cultivars of Hydrangea macrophylla,’Endless Summer the Bride’（aluminum-tolerant cultivar）and’Maman Blue’（aluminum-sensitive cultivar）were used as experimental materials,and the pot experiment was used to simulate the acid rain and aluminum composite treatment to set the acid rain gradient（p H 6.8,p H 5.0,p H 3.0）and aluminum concentration(0,1,2g·kg^-1),to study the effects of acid and aluminum stress on the physiological and biochemical characteristics and elements absorption of Hydrangea macrophylla.,and to compare the differences in acid and aluminum resistance between two varieties.The results are as follows:（1）Weak acid（pH 5）treatment significantly increased the root,stem,leaf and total biomass of Hydrangea,mainly due to chlorophyll a,chlorophyll b,total chlorophyll content and net photosynthetic rate were increased by this treatment,while fluorescence parameters F_v/F_m,ETR,q_p,NPQ was not significantly affected.This indicated that the weak acid treatment favored the photosynthesis and promoted biomass accumulation.The treatment with strong acid（p H 3）and low aluminum（Al 1）did not significantly affect the biomass in the short term.（2）The net photosynthetic rate of Hydrangea was significantly decreased by aluminum treatment and aluminum-acid composite treatment,and the decrease of P_n was subjected to non-stomatal limitation.With increasing degree of stress,F_v/F_m,ETR,q_p showed a decreasing trend,while NPQ increased.This illustrated that the excess light energy was consumed through heat dissipation to adjust to protect the photosynthetic mechanism.The addition and intensity of acid rain increased the damage of aluminum toxicity to the photosynthetic apparatus.The high concentration of aluminum and the combination of high aluminium and acid treatment significantly reduced the biomass of’Maman Blue’.（3）Acid-aluminum stress caused increased membrane permeability of cells,and compound stress harmed cells more than single-factor contamination.Hydrangea mainly removed active oxygen by increasing the activities of POD and CAT in the antioxidant enzyme system,and increased the content of soluble sugar for osmotic adjustment.（4）Both aluminum and compound treatments significantly increased the accumulation of aluminum content in the plant.Acid rain promoted the absorption of aluminum.The accumulation of aluminum in various parts of the plant was as follows:root>stem>leaf.Acid-aluminum stress had little effect on the Mg content of’Endless Summer the Bride’.High aluminum and its composite treatment with acid obviously inhibited the uptake of Mg by the root of’Maman Blue’.High concentration of aluminum stimulated the absorption of Fe,and Fe mainly accumulated in the root of the plant.（5）The differences in aluminum tolerance between different Hydrangea varieties are mainly reflected that in the high intensity of acid-aluminum stress,compared to’Maman Blue’,’Endless Summer the Bride’has a smaller decrease in P_n,G_s,q_p,a smaller increase in relative conductivity,a higher increase in NPQ,SOD,POD activity and soluble sugar content,a smaller degree of growth inhibition,and a slower increase in aluminum uptake.