Characteristics and impacts of elements in rhizosphere in multiple heavy metals polluted rice paddy soil

【Objectives】 The concentrations of heavy metals in the paddy soils and rice seed exceeded remarkably the standard of soil and food quality of China in the Dabaoshan, Shaoguan city, Guangdong province. This influenced the health of local people and social security. The experimental objective was to investigate the biomass, metal accumulation in different parts of rice in the rhizosphere in paddy soils polluted by combined heavy metals. The correlations between metal concentrations, speciation and transformation could help understanding the potential influence of rhizosphere soil on accumulation, transformation of heavy metals and rice biomass.【Methods】 A pot trial was conducted and 20 rice cultivars were grown in the polluted soils. The rhizosphere soils and non-rhizosphere soils were separated by rhizo-bag. The experimental rice cultivars were planted in the soils of rhizo-bag and harvested after 60 days. The root length, shoot height, metal contents in the different parts of rice, available metal contents in the rhizosphere and non-rhizosphere soils were measured. 【Results】 The accumulation factors of Fe, Cu, Pb, Zn and As were greater in roots than those in stems and leaves. The accumulation ability of heavy metals was in the order: Zn Cu As≈Pb≈ Fe and Fe Zn As Cu Pb in shoots and roots of rice, respectively. The concentrations of available metals in the rhizosphere and non-rhizosphere were in the order: Fe Cu Pb Zn As. Available Fe, Cu and Zn concentrations restrained the dry weight of whole plant with the effect followed the order of Cu Zn Fe. These elements had the strongest influence on rice growth, due to the fact that they are the essential elements for plant, with the available Cu concentrations accelerated plant growth. The available As and Fe concentrations had great influence on Fe accumulation in rice roots where As concentrations restrained, while available Fe concentrations accelerated Fe accumulation. The effect was stronger at available As concentrations than of available Fe concentrations. 【Conclusions】The available Fe concentrations had negative effects on the plant height, dry weight of shoot and root. The available Cu concentrations in rhizosphere soil had the remarkably positive effect on the rice growth. The available As concentrations in rhizosphere and the available Zn concentrations in non-rhizosphere had negative effects on the Fe accumulation in roots, while the available Fe concentrations in rhizosphere and the available Cu concentrations in non-rhizosphere had positive effect on Fe accumulation in rice root. In non-rhizosphere soil, the available Fe and Zn concentrations enhanced the root length.