[Effect of Particulate Organic Matter on Cadmium Uptake and Transport in Rice]

A pot experiment was carried out to investigate the effects and mechanism of particulate organic matter (POM) on cadmium uptake of rice on purple paddy soil. Organic carbon content in soil and POM and Cd content in POM and rice were analyzed. The results showed that the contents of total soil organic carbon (SOC), dissolved organic carbon (DOC), organic carbon in POM (POM-C), Cd in POM (POM-Cd), and the Cd enrichment factor in POM increased with the application of POM. When POM was applied at a rate of 2.5 g·kg^-1, the proportion of POM-C and POM-Cd in soil significantly increased. Application of POM also increased rice plant biomass and enhanced the accumulation of Cd in rice. The Cd content was reduced by 24%-42% in rice roots and increased by 9%-30% in rice shoots with POM application, whereas it was reduced by 17% and 36% in rice grains when the application of POM was 0.5 g·kg^-1 and 1.0 g·kg^-1, respectively, but increased by 39% when the application of POM was 2.5 g·kg^-1. Application of POM had no significant effect on the distribution of Cd in rice roots and shoots, but significantly affected the distribution of Cd in rice grains. The transportation of Cd from shoots to grains was inhibited at low rates of POM, but was promoted at high rates of POM, and consequently increased the Cd content in rice grains. Correlation analyses showed that the content of soil available Cd was the main factor affecting Cd accumulation in rice shoots, and the total content of POM-Cd in soil was the main factor affecting Cd accumulation in rice grains. Therefore, the addition of POM to soil could affect the Cd uptake of rice by changing the content of SOC, DOC, POM-C, POM-Cd, and available Cd in paddy soil.