Effect Of Simulated Acid Rain On Ecophysiology Of Flowering Shrub Seedling In South China

As a shrub mainly observing flowers or leaves,flowering shrubs are of great value in economy and ecology.As the flowers and leaves of flower shrubs are of great aesthetic value,acid rain will damage the leaves and flowers of plants,causing them to produce damage spots,yellowing and other adverse effects.Therefore,it is significant to study the growth of flowering shrubs under acid rain stress.This test in Hibiscus Rosasinensis,Allemanda cathartica,Calliandra haematocephala and Jatropha integerrima for experimental object,by simulating a mild acid rain(pH4.5),moderate acid rain(pH3.5),severe acid rain(pH2.5)stress test to study plants in growth,photosynthetic characteristics,leaf and physiological and biochemical changes in the mineral elements content.Results are as follows:(1)The effect of acid rain on plant growth showed that the plant height growth and biomass of four flowering shrubs decreased with the increase of acid rain concentration.Among them,the plant height growth of the four flowering shrubs was the lowest of the four gradients under the stress of severe acid rain,which was significantly different from the control group(P < 0.01).(2)The effect of acid rain on the photosynthetic characteristics of plants indicates that the concentration of acid rain is negatively correlated with the relative content of chlorophyll in plants.Under mild acid rain stress,the relative chlorophyll content of both Allemanda cathartica and Jatropha integerrima was the highest among the four gradients,but there was no significant relationship with the control group(P > 0.05).Stomatal conductance and chlorophyll fluorescence parameters were negatively correlated with acid rain concentration on the whole,but the resistance of different plants to acid rain was also different.(3)The effect of acid rain on the leaf element content of plants showed that the relationship between the content of mineral elements in the leaves of four flowering shrubs and the acid rain concentration was not obvious.For example,the content of N element in the leaves of Jatropha integerrima was the highest in the control group;The content of N element in Hibiscus rosa-sinensis leaves was positively correlated with the concentration of acid rain.Under severe acid rain stress,the content of N element in Hibiscus rosa-sinensis leaves was the highest,indicating that different plants have different absorbability to different mineral elements.(4)The effects of acid rain on plant physiology and biochemistry showed that different concentrations of acid rain stress had different effects on the pH value of plant leaf juice.The pH value of acid rain was positively correlated with the pH value of Calliandra haematocephala leaf juice.The lower the pH value of acid rain was,the lower the pH value of Calliandra haematocephala leaf juice was.The pH value of leaf juice of each acid rain gradient was significantly correlated with that of the control group.Under the acid rain stress,the ratio of free water and bound water of plants was higher than that of the control group.The change range of Hibiscus Rosa-sinensis between different gradients was small,but the change range of Calliandra haematocephala was large,indicating that the resistance of Calliandra haematocephala was weaker than that of Hibiscus Rosa-sinensis.According to the above plant physiological indexes,acid rain has a great effect on flowering shrubs.Among them,severe acid rain will adversely affect plant growth,photosynthesis and a series of physiological and metabolic activities.The effects of acid rain with other gradients on plants vary with plant varieties.