| A large amount of arsenic-containing waste water was discharged into the environment with the development of industry and agriculture and the use of pesticides and insecticides,leading to serious arsenic pollution for soil and underground water.Furthermore,highly toxic trivalent arsenic[As(Ⅲ)]is the main form of rice rhizosphere when it is cultivated under flooded conditions.Therefore,to reduce the toxicity of As(Ⅲ)for rice seedling has very important significance for rice yield and quality.In this study,four rice varieties,namely Shanyou 63,Minghui 63,Guangyou Ming 118 and Teyou Hang II,were chosen as research materials to investigate the effects of arsenite-oxidizing bacteria CRS003,which was screened from paddy soil by our own research group,on their photosynthetic physiology,morphology and protective enzyme activities stressed by As(Ⅲ)through hydroponics.As(Ⅲ)oxidation rate,pH value and nutrient intake of NH4+、NO3-、HPO42-and K+ were monitored with or without CRS003 in the hydroponic nutrient solution stressed by As(Ⅲ).Moreover,nutrient intake of N,P,K,migration and accumulation of arsenic pollutants by rice roots and leaves were determined and the mechanism how to reduce the toxicity of As(Ⅲ)for rice seedling by CRS003 was analyzed.The main results were as follows:(1)CRS003 significantly reduced the toxicity of As(Ⅲ)for the growth of rice seedling.Compared with As(Ⅲ)poisoning test group without CRS003,the recovery rates of those physiological and biochemical properties such as chlorophyll SPAD value,root length,plant height,dry matter weight of rice seedling roots/leaves,SOD,POD and CAT were all dramatically increased except the dry matter weight of Guangyou Ming 118 roots and MDA content was significantly reduced when CRS003 was 0.25%(v/v)inoculated into the hydroponic nutrient solution of four varieties and stressed by As(Ⅲ)for 6 d.CRS003 had the best repair effect on the toxicity of As(Ⅲ)for Shanyou 63 among four varieties.(2)CRS003 significantly increased the oxidation rate of As(Ⅲ)in hydroponic solution stressed by As(Ⅲ).The results showed that As(Ⅲ)oxidation rate of Shanyou 63 was the highest,about 72%,the second was Teyou hang Ⅱ,about 40%,only 37%and 30%for Guangyou Ming 118 and Minghui 63,respectively,after the hydroponic solution was stressed by 3 mg-L-1 As(Ⅲ)for 6 d without CRS003.However,As(Ⅲ)oxidation rates of four varieties were all 100%after CRS003 was 0.25%(v/v)inoculated into the hydroponic solution and stressed by 3 mg·L-1 As(Ⅲ)for 6 d.(3)CRS003 significantly reduced the pH value in hydroponic nutrient solution of four varieties stressed by As(Ⅲ).The results showed that pH value in hydroponic nutrient solution of four varieties was increased from 5.5 to 5.8-6.1 after stressed by 3 mg·L-1 As(Ⅲ)for 6 d without CRS003,about 0.3～0.6 pH unit increased.However,pH value in hydroponic nutrient solution of four varieties were reduced from 5.5 to 4.2～4.7 when CRS003 was 0.25%(v/v)inoculated into the hydroponic nutrient solution and stressed by As(Ⅲ)for 6 d,about 0.8～1.3 pH unit reduced,nearly same as CK control without As(Ⅲ).(4)CRS003 significantly increased the absorption of NH4+、NO3-、HPO42-and K+in hydroponic nutrient solution and the content of N,P and K intaked by the roots/leaves of Shanyou 63,Guangyou Ming 118,Teyou Hang II and the leaves of Minghui 63 except that the content of P nutrients intaked by the roots of Minghui 63 was reduced.CRS003 had the highest promotion effect on the N,P and K intakes by the roots/leaves of Shanyou 63 among four varieties.(5)CRS003 significantly reduced the total As content in the roots of Guangyou Ming 118 and Teyou Hang Ⅱ,however,increase the total As content in the roots of Shanyou 63 and Minghui 63.The results of As speciation showed that the percentages of As(Ⅲ)accumulated by the roots of Guangyou Ming 118,Shanyou 63 and Minghui 63 were all dramatically reduced by CRS003 except that the percentages of As(Ⅲ)accumulated by the roots of Teyou Hang Ⅱ were increased.The percentages of As(Ⅲ)accumulated by the roots of Shanyou 63 was the lowest among four varieties and the value was zero,namely,no As(Ⅲ)was detected in its roots.(6)CRS003 didn’t significantly reduce the total As content in the leaves of four varieties.Compared with As(Ⅲ)poisoning test group without CRS003,The transportation ratio for total As content from roots to leaves was increased for Guangyou Ming 118,Teyou Hang II and Minghui 63,however,The transportation ratio for total As content from roots to leaves was reduced for Shanyou 63 and the total As content accumulated by its leaves was minimum among four varieties when CRS003 was 0.25%(v/v)inoculated into the hydroponic nutrient solution of four varieties and stressed by As(Ⅲ)for 6 d.The results of As speciation showed that the percentages of As(Ⅲ)accumulated by the leaves of Shanyou 63 was also minimum among four varieties.In a word,the chemical speciation of As pollutants in rice growing environment is the key to determine its toxicity and mobility.Highly toxic As(Ⅲ)was quickly oxidized into As(V)and pH value was greatly reduced by CRS003 when it was inoculated into the hydroponic nutrient solution stressed by As(Ⅲ).Therefore,the toxicity of As(Ⅲ)for the growth of rice seedling was reduced and the physiological and biochemical properties of four varieties were all dramatically renovated.Among the renovation test groups of four varieties by CRS003,the total contents of N,P,K intaked by Shanyou 63 roots and leaves were the highest,however,the percentages of As(Ⅲ)accumulated by Shanyou 63 roots and leaves were the lowest and the total As content was also minimum in Shanyou 63 leaves.Therefore,CRS003 had the best repair effect on the toxicity of As(Ⅲ)for Shanyou 63. |
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