The Differences Among Rice Cultivars In Tolerance And Accumulation And Distribution To Soil Cadmium

In order to investigate the differences among rice cultivars in tolerance, accumulation and distribution on cadium (Cd) in soil, a pot experiment was conducted with 20 rice cultivars of different genotypes and origins by adding 100 mg/kg Cd to soil And the main results showed as follows:(1 )The principal toxic effects of Cd on rice before heading were the reduction of the photosynthetic production and chlorophy synthesis as typical features: small plants, yellowed leaves and emaciated vegetation. In the stage from heading to ripening . the maim phytotoxicity of Cd was inhibition of the differentiation and development of the reproductive organs which lead to decrease of spikelets per panicle, filled grain percentage and grain percentage and grain yield. And the levels effected by Cd varied greatly with different rice cultivars. For example, the yields of 20 rice cultivars decreased by 1-48%,(2)The abilities of the rice cultivars in Cd accumulation remained consistent between before heading and after heading. The Cd accumulation and distribution in the organs of rice plant differed with rice cultivars and genotypes, and the proportion of Cd absorbed by rice plant varied with different organs.(3)Among the cultivars there existed significant differences in Cd accumulation and the differences were significantly concerned with rice genotypes organs and growing stages. In different organs and stages , The Cd concentrations and accumulation speed were greatly different . Cd concentrations fell rapidly from root to brown rice along rice plants . Proportion of Cd absorbed by rice plant in root ,stem.leaf and ear was 92: 3.: 1: 1 at heading and 617: 52: 12: 1 at ripening ; the regress analysis showed that there were negative correlations between the organs of rice plant at heading ,but positive correlations at ripening .(4) The concentrations of Cd were very low in brown rice compared with other parts of rice plants , so only a very small proportion of Cd absorbed by rice plant was transported to brown rice, so the Cd concentration in brown rice was only 1/47 of that in straws averagely. Cd concentrations in brown rice also varied among rice genotypes, and the sequence was Indica>New Plant Type>Japonica. The Cd concentrations and accumulation speed in brown rice both correlated significantly with grain yields and spikelet per panicle among the rice cultivars. Cadmium was not distributed uniformly in different parts of grain structure, and the cadmium accumulation in polished rice decreased by 35% than the cadmium accumulation in brown rice.(5)There existed significant differences among the rice cultivars in the contents of six mineral elements Cd2+ , Fe3+. Zn2+ ,Cu2+ , Mn2+, Mg2+ in both roots and leaves at both heading and ripening periods .The statistical analysis showed that ,for their contents in roots, significant and positive correlations between Cd2+ and Fe2+, Cd2+ and Mn2+, Cd2+ and Zn2+. Cd2+ and Cu2+ existed ,but no significant correlation between Cd2+ and Mg2+ at two periods. In the leaves, Cd also showed significant and positive correlations with Fe2+. Zn2+. Cu2+ at the both period ,but There were differences in correlation with Mn2+ and Mg2+ at two stages . These results suggested that there were cooperative absorption between Cd2+ and Fe3+, Zn2+ ,Cu2+ , Mn2+ in rice plants.