A pot experiment with rice under submerged condition showed that with the increase of Cd concentration, soil microbial biomass carbon (Cmic) and nitrogen (Nmic) increased initially but decreased at a certain concentration, and the turning points varied with different soil types. Soil enzyme activities had the similar variation trend with soil Cmic and Nmic, and the turning points varied with different soil types and soil enzymes. The variation coefficients were in order of dehydrogenase activity > acid phophatase activity > urease activity. Soil respiration rate and metabolic quotient increased tardily with increasing cadmium concentration. The chlorophyll content of rice increased initially but decreased then with the increase of Cd contamination, and the turning points differed with different soil types. Rice proline content and peroxidase activity were enhanced gradually with increasing cadmium concentration. The variation coefficients of rice physiological indices on paddy soils derived from silty loam and clayed red earth were in order of peroxidase activity > chlorophyll content > proline content, and peroxidase activity > proline content > chlorophyll content, respectively. Correlation analysis indicated that there was a close correlation between the variations of soil microbial biomass and enzymatic activities and rice physiological indices under Cd contamination.
Cadmium Oryza