| Rice, a staple food, is a significant dietary source of inorganic arsenic. Paddy rice is more likely to suffer from As-stress than other cereal crops. Practical measures are needed to mitigate the adverse effect of As to paddy rice. Three potential mitigation methods, management of the water regime, P fertilization and their interaction, were investigated through soil culture experiments with rhizo-box. The main results were as following:1. Both rice cultivars had the largest plant height, number of tillers, total spike, productive spike, shoot dry weight and grain yield under water-saving irrigation condition with sufficient P fertilization regardless of As levels. Compared with flooded conditions, Alternation of Drying-Wetting significantly increased the above biological characteristics and grain yield of rice.180mg·kg-1of P2O5treatment also enhanced the growth of rice markedly compared with30mg·kg-1of P2O5addition. The mitigating effect of water management regime on As-stress to rice was clearer under high As and/or low P conditions than its contrary conditions. For P fertilization, the mitigating effect was more obvious under flooded condition than alternation of wetting and drying, and more pronounced for low-P sensitive rice cultivar than its low-P tolerant counterpart. The interaction of water management and P fertilization showed positive effect, and the positive effect was more significant under high As condition than low As condition, and more significant for low-P sensitive rice cultivar than low-P tolerant rice cultivar. At50mg·kg-1of As level, the mitigating effect of P fertilization for the economical character and grain yield was stronger than that of water-saving irrigation. At100mg·kg-1of As level, the mitigating effect of P fertilization for tillers, productive spike and grain yield was weaker than that of water-saving irrigation, but plant height, total spike and shoot dry weight was on the contrary. The enconomical characters and grain of low-P tolerant rice cultivar99011were much better than those of low-P sensitive rice cultivar99012at the treatments with As supply.2. Water-saving irrigation decreased the As concentration in iron plaque and all organs of rice (including root, shoot, husk and polished rice) of both rice cultivars compared with submergence treatments regardless of As levels. At50mg·kg-1of As level, sufficient P addition clearly reduced the As concentration in all organs of low-P tolerance rice cultivar99011compared with insufficient P supply, but increased the As concentration in polished rice of low-P sensitive rice cultivar99012. Sufficient P addition obviously reduced the As concentration in all organs of two rice cultivars at100mg-kg-1of As level. The mitigating effect of water management on As-stress to rice was clearer under high As conditions than its contrary conditions. For P fertilization, the mitigating effect was more obvious under flooded condition than water-saving condition, and more significant for low-P sensitive rice cultivar than low-P tolerant rice cultivar. The interaction of water management and P fertilization showed positive effect, and the positive effect was more marked under high As condition than low As condition, and more significant for low-P tolerant rice cultivar than low-P sensitive rice cultivar.3. Fe-As is the main As-fraction in acid soil, and followed by O-As, Res-As, Ca-As Al-As, and As extracted by NH4Cl (NH4Cl-As) orderly. The concentration of NH4C1-As, Al-As and Ca-As in the rhizosphere were higher than those in the close-, medium-and remote root zone, but Fe-As, O-As and Res-As was on the contrary. Compared with flooded conditions, Alternation of Drying-Wetting significantly increased Al-As, but reduced NH4Cl-As and Fe-As.180mg-kg-1of P2O5treatment increased the Al-As markedly, but decreased the Res-As compared with30mg-kg-1of P2O5addition.. The concentration of As(III) was higher than As(V) in the soil solution at the treatments with As supply. Water-saving irrigation reduced the concentration of As(III) in the soil solution markedly compared with flooded condition. Sufficient P fertilization increased the As(III) in the soil solution, and reduced the As(V) markedly at100mg-kg-1of As level. The effect of water management, P fertilization and their interaction on As(III) and As(V) showed different effect, and was led by water management effect.The study demonstrated that water management, P fertilization, and selection of rice cultivars are effective measures that can be used to reduce the availability of As in acid soil, relieve the As stress to rice and improve the safety of food. |
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