Effects Of Different Water Management Methods On Cadimium Uptake And Translocation By Rice With Different Grain Accumulation Characteristics

Rice (Oryza sativa) is globally one of the most important food crops. In recent years, contamination of arable soils by cadmium (Cd) is more serious with the rapid development of industry and agriculture, which affects rice grain yield and its edible risk. Rice shows considerable genotypic variation in Cd accumulation in grains. A promising for reducing the Cd concentration in rice grains is breeding or engineering low-Cd accumulating cultivars. This requires a prior understanding of the Cd accumulation mechanisms in rice plants. Agronomic regulation is the effective approach for reducing grain Cd concentration in Cd contaminated soil. Research has shown that flooding reduced cadmium concentrations in rice grains, whereas aerobic treatment increased the concentration of cadmium. A hydroponic culture and a pot experiment were conducted, using two rice varieties with different grain Cd accumulation characters, to investigate the rice Cd uptake and translocation and the plant physiological mechanisms. Another pot experiment and a field experiment were conducted to investigate influence of different water management methods on Cd uptake and translocation by rice and the mechanisms. The main results were showed as follows.1. Uptake and translocation of Cd by two rice cultivars with different grain accumulation characters and the relevant physiological effectsA hydroponic culture and a pot experiment were conducted, using two rice cultivars with different grain Cd accumulation characters, to investigate Cd uptake and translocation in rice and their physiological effects in several growth stages. In the pot experiment, the grain Cd concentrations of A16 and A54 were 0.31 mg kg-1 and 0.88 mg kg-1, respectively, when soil total Cd concentration was 1.57 mg kg-1. Both hydroponics culture and pot experiment showed that A16 absorbed and translocated more Cd than A54 during the seedling stage. However, after the seedling stage, the amounts of Cd uptake and translocation by A54 were higher than A16. Root Cd sequestration and rhizosphere soil properties may explain the differences by rice Cd absorption and translocation between the seedling stage and other stages. From the comparison of Cd accumulation in rice of two cultivars at various growth stages, it was observed that the increase from the seedling stage to jointing stage was the highest. Therefore, this may be the key period for Cd uptake and accumulation for both cultivars. By analyzing the shoot and root Cd concentrations, Cd translocation rate from roots to shoots and non-protein thiol (NPT) that can sequestrate Cd within the root in different growth stages, we found that the difference in grain Cd concentrations of A16 and A54 could be attributed to root uptake and translocation to shoot of rice.2. Influence of different water management methods on Cd uptake and translocation by rice and the mechanisms in a pot experimentA pot experiment was conducted to investigate effect of irrigation models of flood, intermit and aerobic irrigation on rice Cd uptake and translocation and the mechanisms. Results showed that flooding significantly reduced soil HCl extractable Cd, and roots and shoots Cd in rice. This could be interpreted as the decrease of soil HCl extractable Cd and the Fe2+ competition in adsorption by iron plaque of rice root and absorption by rice root. In addition, the formation of precipitatable CdS under flooding condition influenced the soil available Cd, to a great extent.3. Influence of different water management methods on Cd uptake and translocation by rice in a field experimentA field experiment was conducted, using two rice cultivars with different grain Cd concentrations, to investigate the influence of waterflooding during the whole growth stages (W), local production irrigation method (CK), intermit irrigation (I) and no irrigation drought (D) on Cd uptake and translocation in rice and the mechanisms. Results showed that compared with CK, "W" reduced soil HCl extractable Cd, and Cd concentrations in the root, shoot, husk and brown rice, whereas, "I" and "D" enhanced the above indexes.Compared with CK, treatments of "W", "I" and "D" increased grain yields of A16 74.9% (p< 0.05),61.9%(p<0.05) and 49.0% respectively; As for A159, "D" treatment increased 9.18% (p<0.05), while, "W" and "I" decreased 7.76% (p>0.05) and 1.05% (p>0.05), respectively. The increase of grain yields of both the tesed rice varieties under "D" treatment could be explained as D treatments enhanced the 1000-grain weight.Compared with A16, the brown rice Cd concentration of A159 increasd 1.14 (p<0.01), 1.56 (p<0.01),0.602 (p<0.01) and 0.389 (p>0.05) respectively under CK, W, I and D treatments.