| Acid rain and heavy metal cadmium（Cd）pollution have become major problems affecting human health and environmental safety.At present,there are few studies on the effects of acid rain and Cd on lawn plants.In this study,Bermuda grass,a turf plant with Cd tolerance,was used as the research object.Two groups of hydroponic experiments were carried out under different concentrations of Cd alone stress and combined stress of Cd and acid rain,as well as the hydroponic experiment of adding exogenous calcium（Ca）.The effects of Cd and acid rain stress on physiological and biochemical characteristics of Bermuda grass seedlings and the regulation of exogenous Ca were systematically studied.The results provide a theoretical basis for remediation of soil Cd pollution by plants in acid rain polluted areas.The main conclusions are as follows:（1）Acid rain inhibited the growth of Bermuda grass and intensified the toxicity of higher concentration of Cd to Bermuda grass.Under the same concentration of Cd,the chlorophyll content of Bermuda grass treated with higher concentration of Cd and acid rain decreased,the contents of soluble protein,soluble sugar and free amino acid increased,the content of malondialdehyde（MDA）increased,and the activity of superoxide dismutase（SOD）increased compared with the plants treated with Cd alone.Both Cd and acid rain stress disrupted nutrient distribution patterns in the aboveground parts of plants.Under the same concentration of Cd,the combined treatment of Cd and acid rain increased the content of nitrogen（N）in shoot,but decreased the content of phosphorus（P）,potassium（K）and Cd in shoot,especially the content of Cd in leaves.In conclusion,Bermuda grass has a certain tolerance to the combined stress of heavy metal Cd and acid rain,and the treatment of 1mg L-1 Cd and p H4.5 simulated acid rain has the most serious damage to Bermuda grass.Acid rain intensified the toxic effect of Cd on Bermuda grass seedlings.（2）The addition of exogenous Ca alleviates the damage of Cd and acid rain to plants to a certain extent.Compared with the plants under the combined stress of Cd and acid rain,adding exogenous Ca improved the growth of Bermuda grass（root length,plant height,stem node length,leaf length,leaf width,root dry weight,stem dry weight,leaf dry weight and total dry weight）.The relative chlorophyll content,soluble protein and soluble sugar contents,SOD,POD and CAT enzyme activities were increased,and MDA content was decreased.Meanwhile,the contents of N,P and K in each organ of Bermuda grass were increased.Under p H4.5 acid rain and Cd stress,the plant parameters of the treatment group with exogenous Ca(5mmol l-1)were close to the control level.In addition,the application of exogenous Ca increased the absorption of Cd in Bermuda grass to a certain extent,and promoted the transfer of Cd to the aboveground part of the plant.Therefore,exogenous Ca can alleviate the inhibition of Cd and acid rain on plant growth by increasing chlorophyll content,activating antioxidant enzyme activity,promoting the absorption of nutrients and promoting the transfer of Cd to aboveground,but its alleviating effect is limited by acid rain intensity. |
