Effects Of Different Inorganic Arsenic Sepecies On The Growth Of Rice Seedling And Soil Microbes

The issue of arsenic contamination of rice is an important problem about human health. Accumulated Arsenic in soil will not only change the properties of soil, affect the yield and quality of rice, but also endanger human health ultimately through the food chain.Two rice accessions, rice Shanyou 63 and Minghui 63 were chosen as the test material to explore the effects of inorganic arsenic on the growth of rice seedlings. As(â…¢) (As₂O₃) and As(â…¤) (Na₂HAsO₄) were added to the paddy soil at 0 mg / kg(soil), 60 mg / kg (soil) and 120 mg / kg (soil) respectively. The morphology and photosynthetic physiological characteristics of rice seedling were detected in the greenhouse experiment. The physiological and biochemical characteristics of soil and the rhizosphere microbes of rice seedlings were further analysed. The results were summarized as follows:1. The root length, plant height and dry weight of the two rice seedlings were significantly inhibited after treated by inorganic arsenic. Taking rice Shanyou 63 treated with 120mg/kg (soil) arsenic as an example, the root length, plant height and dry weight of rice seedling were decreased by 43.37%, 38.65%, 51.31% respectively after treated with As (â…¢) compared with the control, while decreased by 31.72%, 23.75%, 37.50% after treated with As(â…¤). So the effect of inorganic arsenic on the dry weight of rice was the greatest, followed with the root length, and the effect on the plant height was least. As (â…¢) was more toxity to rice seedlings than As(â…¤) .2. After treated with inorganic arsenic, the photosynthetic physiological indices of rice seedling were decreased, the activities of the key enzymes in rice photosynthesis were decreased, and the genes encoding for the key enzymes in photosynthesis of the two rice seedlings were all down-regulated expressed. Taking rice Shanyou 63 treated with 120mg/kg (soil) arsenic as an example, compared with the control, the net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, transpiration rate, stomatal limitation value, chlorophyll content were decreased respectively by 60.15%, 42.05%, 30.38%, 50.94%, 51.33%, 44.73%, and the activities of the key enzymes in photosynthesis, such as Ribulose 1,5-bisphosphate carboxylase (RuBPcase), Phosphoenolpyruvate carboxylase (PEPC) and Glycolate oxidase (GO) were decreased respectively by 59.59 %, 56.27%, 47.31%, and the down-regulated folds of the three genes encoding the three key enzymes (RuBPcase, PEPC and GO) were 8.69, 6.72, 5.38 respectively after treated with As (â…¢). While after treated with As(â…¤), the net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, transpiration rate, stomatal limitation value, chlorophyll content were decreased respectively by 38.46%, 23.11%, 21.10%, 27.36%, 24.45% , 33.72%, and the activities of RuBPcase, PEPC and GO were respectively by 47.70%, 36.45%, 38.25%, and the down-regulated folds of the three genes encoding the three key enzymes (RuBPcase, PEPC and GO) were respectively 5.86, 3.79, 3.81. So the photosynthesis of rice seedling were inhibited significantly after treated by arsenic, and the effect of As (â…¢) on the photosynthesis of rice was greater than that of As (V).3. Inorganic arsenic could inhibit the microbial biomass C (MBC), the microbial respiration rate (MBR) and the activities of various soil enzymes. Taking the soil of 120mg/kg (soil) arsenic which planted the rice Shanyou 63 as an example, that is, compared with the control soil, the MBC and MBR were decreased respectively by 45.83%, 44.83%, and the activities of urease, protease and invertase were decreased respectively by 56.35%, 53.54%, 60.78% after treated by As(â…¢). While the MBC and MBR were decreased respectively by 31.06%, 26.03%, and the activities of urease, protease and invertase were decreased respectively by 48.28%, 38.19%, 43.71% after treated by As (V). The result of the effect of inorganic arsenic on microbial flora showed that inorganic arsenic inhibited the number of bacteria, fungi and actinomycetes in the soil. That is, compared with the control soil, the number of bacteria, fungi and actinomycetes were decreased respectively by 41.13%, 42.60%, 30.05% after the soil was added with As (â…¢), while decreased respectively by 22.61%, 27.22% , 17. 29% after the soil was added with As (V). So we found that inorganic arsenic could inhibit the physiological and biochemical characteristics of soil microbes to a certain extent. And that might be affect the growth and yield of rice indirectly.In conclusion, different inorganic arsenic species could influence the photosynthesis of rice and the physiological and biochemical characteristics of soil microbes significantly. And the behaviors of two rice accessions in response to the stress of inorganic arsenic were similar, showing that the key enzymes in rice photosynthesis were down-regulated, the activities of relevant enzymes were inhibited, and the potential of rice photosynthesis was weaken, thereby resulting in damage of rice seedlings accompany with the decrease of root length, plant height and dry weight of rice seedlings. Moreover, inorganic arsenic affected the soil microbes and activities of relevant soil enzymes, which might indirectly affect the growth of rice seedlings.