| Arsenic is ubiquitous in the environment and is regarded as one of the most serious pollutants. In recent years, soil has been contaminated by arsenic, due to the arsenic ore mining and smelting as well as heavy application of arsenic containing pesticdes.Rice is a sensitive crop to arsenic. It was reported that the arsenic pollution in soil could result in straighthead disease of rice and yield loss seriously. Nitrogen is one of the indispensable nutrient elements for plant growth. The project studied the effects of different N fertilizer(urea)dosage(0-0.4g/kg N) on the plant growth, the yield, the antioxidant system, the C and N metabolism, and the arsenic uptake and bioaccumulation of rice under arsenic(50mg/kg As) stressed condition by employing a pot experiment, in order to investigate the effects and preliminary mechanism of different N level in relieving arsenic toxicity to rice, and provide a scientific basis for rice planting on arsenic contaminated soil and control the straighthead disease of rice. The main results are as follows:1. Arsenic treatment significantly inhibited the growth of rice seedlings, resulting in the fresh weight, plant height and chlorophyll content of rice seedlings were significantly lower than those of control treatment(P <0.05). At the same time, arsenic induced oxidative stress in rice seedlings, resulting in the MDA content of leaves were significantly higher than that of CK treatment(P<0.05). Nitrogen fertilizer application increased the anti-oxidative stress ability of rice seedlings in condition of high concentrations of arsenic stress, resulting in declining the MDA content of leaves, alleviating the toxic effects of arsenic on rice to some extent, and promoting the growth of rice seedlings. The fresh weight and chlorophyll content of rice seedlings increased under arsenic stressed condition with the growth of N application level.2. Arsenic treatment delayed the growing period of rice, and reduced dry weight of aboveground and yield. The panicle numbers, panicle length, grains per spike and yield treated with 50mg/kg As were only 29.1%-60.0%,52.4%-86.0%,31.0-77.9% and 16.5%-22.7% of CK treatment, respectively. Under the conditions of arsenic treatment, the panicle numbers, panicle length, grains per spike and yield of rice increased significantly with the increase of N fertilizer dosage, and reached a maximum value at 0.4g / kg N treatment which were 11.1 times, 1.7 times, 3.75 times and 9.8 times of the treatment without N application, respectively.3. Arsenic stress disturbed the carbon metabolism of rice. Under conditions of low N treatments(≤0.1g/kg N), arsenic significantly increased soluble sugar content of rice leaves(P <0.05). However, under ≥0.2g/kg N conditions, 50 mg/kg As depressed soluble sugar content of rice leaves, and there was no significant difference between As treatment and CK(P> 0.05). In addition, under the conditions without N application, the activities of Sucrose synthase(SS)and Sucrose phosphosynthase(SPS) as well as the content of soluble sugar and sucrose in rice leaves treated with arsenic were significantly higher than those of CK. Application of N fertilizer under arsenic stress reduced the sugar content in rice leaves, and the high dosage of N fertilizer(0.4g/kg N) significantly increased the Sucrose synthase(SS) activity in leaves, and accelerated the carbon metabolic processes, resulting in carbohydrates accumulation in rice.4.The nitrate content and the activities of Nitrate reductase(NR), Glutamine synthetase(GS) and Glutamate synthase(GOGAT) in rice leaves treated with CK increased with the growth of N fertilizer application. Arsenic stress interfered with the N metabolism of rice, broken the positive correlation between the N metabolism indexes and N dosage. Under the conditions of without adding N, the content of soluble protein and the activities of Nitrate reductase(NR), Glutamate synthase(GOGAT) and Glutamate dehydrogenase(GDH) in rice leaves treated with arsenic were significantly higher than those of CK treatment. With the increasing of N fertilizer dosage, the soluble protein content of rice leaves treated with arsenic decreased, while GS activity increased. Application of N fertilizer also increased the nitrate content, but decreased the Glutamate dehydrogenase(GDH) activity in rice leaves under arsenic treatment conditions.5.Arsenic treatment significantly inhibited the uptake and translocation of N in rice. The N content in roots of rice seedlings treated with arsenic was significantly higher, but the N content in shoots and bioaccumulation and transfer coefficient(shoots/roots)was significantly lower than those of control treatment. Arsenic treatment also significantly increased the stem and leaves N content at filling stage and the stem N content at maturing stage. However, the N bioaccumulation of rice stem and leaves treated with As and the transfer coefficient(leaves/stem) were still lower than the control treatment.6.Arsenic stress significantly enhanced As content in shoots and roots of rice seedlings as well as in stem and leaves at filling stage and maturity stage, but decreased the As content in grain and husk. Application of N fertilizer promoted the As uptake of rice, resulting in both the As content and As bioaccumulation of rice stem and leaves were significantly higher than that of without N treatment and the As bioaccumulation increased with the increase of N fertilizer dosage. |
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