Studies On Uptake And Translocation Of Cadmium And Lead In Rice Cultivars And The Effect Of Cultivation Environment

Heavy metal pollution to agricultural production and ecological environment became more and more serious with the social development. And it had definitely put great threaten to agricultural production in many areas. Using different types of rice varieties as materials, characteristics of different crop cultivars in uptake and translocation of cadmium (Cd) and lead (Pb) were observed. A further research on the effect of cultivation environment of uptake, accumulation and translocation was also studied, by selecting typical rice cultivars performed differently in uptake. The objectives of this study were acquaint the knowledge on variations among rice cultivars that grown in the heavy metal polluted soil in uptake and translocation of Cd and Pb, and obtain an updated knowledge on the cultivation effects to heavy metal accumulation, this research also explored a deep analysis on several physiological indices of rice growth. The main results were as follows:1. There were wide variations among rice cultivars in Cd and Pb accumulation. The average strength of accumulated Cd in Indica rice was the highest, and the strength in Hybrid rice was higher than that in Japonica rice. Obviously, there were abundant genotypes existing in ordinary Indica and Japonica rice. There were in brown rice as well. But the cultivars with low accumulation were a majority. 84% of the tested cultivars showed lower than 1.0μg g-1 Cd accumulation in brown rice in 100 mg g-1 Cd treated soil, indicating a great room in selecting rice cultivars in low accumulation of Cd. By reference of the density index of Cd in steam, sheath, and brown rice, a cluster analysis was used. The tested cultivars were divided into four groups. GroupⅠ, brown rice with high accumulation, GroupⅡ, brown rice with low accumulation, GroupⅢ, uptake rejection, GroupⅣ, richness in accumulation. There were also abundant genotypes of cultivars in accumulation of Pb. The average strength of accumulated lead in Indica rice was the highest, and the strength in Hybrid rice was a little bit higher than in Japonica rice. 80% of the tested cultivars showed about 0.1~0.9μg g-1 Pb accumulation in brown rice in 1000 mg g-1 Pb treated soil. And the Cluster Analysis showed the tested cultivars could be divided into four types as well.2. The nitrogen fertilizer had significant effects on biological effect and the capability in uptake and accumulation of heavy metals in rice plan. Furthermore, the fertilizer level had remarkable effects on dry matter production during the three developing stages. This level also had significant effect on grain yield. High density of Cd induces the low yield, while nitrogen fertilizer could alleviate this phenomenon. The observation of the nitrogen fertilizer effect on the accumulation of Cd in rice plant clearly showed that nitrogen fertilizer went through the whole rice developing duration and had significant effect on its accumulation of Cd. High-level nitrogen fertilizer had two functions to Cd accumulation in each period of rice developing duration, i.e. great promotion and unnoticeable effect. Nitrogen fertilizer could accelerate the distribution of the accumulated Cd to each part of the grain. The increase in Cd in milled rice was especially remarkable. Regarding the accumulation of Pb, the same trend was observed. Nitrogen fertilizer had significant effect on biological effect caused by Pb during rice developing duration, and there were remarkable variations among cultivars. By analyzing the production of dry matter, the effects of fertilizer to the growth of rice under the stress of lead were divided into two types: Restore Type and Inactivity Type. In the soil treated with Pb, there was a decreasing trend in the yield of the 7 Cultivars except for Nipponbare and Liangyoupeijiu. Nitrogen fertilizer did increase the yield of each cultivar. This result showed nitrogen fertilizer had the evident remediation effect on injury by Pb. The effect of nitrogen fertilizer on accumulation of Pb differed with cultivars. It promoted the accumulation of Pb or had no significant effect. High fertilizer level promoted the accumulation of lead to the stem and milled rice synchronizing or asynchronously.3. Water stress had significant effects on biological effect caused by heavy metal (Cd and Pb), and the influence varied with rice cultivars. Generally, water stress had significant inhibiting effect on dry matter weight under the stress of heavy metals (Cd and Pb). Water stress had inhibiting effect on yield of rice under stress of Cd or Pb, and this inhibiting effect usually strengthened or was unremarkable under water stress. Water stress inhibited or accelerated accumulation of Cd and Pb remarkably. And it usually promoted the accumulation of Cd in rice plant and grain, but there were great difference among cultivars. Water stress also had obvious effect on accumulation of Pb in rice plant and grain, but there were three types of tested cultivars, i.e. the promoting effect, inhibiting effect and no significant effect. Water stress had little effect on accumulation of Pb in milled rice, but significantly accelerated accumulation of lead in Rice bran.4. On the soil treatment of Cd and Pb, several morphological and physiological indices of rice were significantly changed, but the influence degree varied with rice cultivars, and the Influence of Cd was nearly consistent with Pb, Under Cd and Pb Stress, there was evident decrease trend in plant height and the tiller numbers. Root activity decreased, and it was negative correlated with heavy metal accumulation. But the conductivity of root exudates increased, and it had positive correlation with heavy metal accumulation. The MDA and Free Proline content in leaf increased, and soluble sugar content in leaf also increased. It apparently had positive correlation with heavy metal accumulation in rice plant.