Effects Of Soil Sulfuric Behavior On Cadmium Uptake And Accumulation In Rice Growth Period And Activity Of Soil Enzymes

The soil sample was taken from the multi-metal contaminated paddy soils due to the irrigation of acid mine drainage for more than40years. The two rice varieties that rice Oryza sativa L. cv. Choukoukoku (OSC) and Oryza sativa L. cv. Jinnongsimiao (OSJ) which has a high and low absorption capacity of cadmium, respectively was selected for studying. The speciation and transformation of sulfur and distribution of Cd and soil enzymes activities in rhizosphere soil of two rice varieties at four growth stages (tillering stage, booting stage, flowering stage and milk ripening stage) were investigated by using multiple lattice layer rhizobox system. The aim of our study was to clarify the interaction relation of soil sulfur forms with accumulation of cadmium in rice, distrubition of Cd in soils and soil enzymes through correlation analysis. The main results were as follows:(1) The soil hydrochloric acid extracted sulfur contents increased and pyrite, organic sulfur, total sulfur, total Cd and available Cd contents decreased gradually with the growth of two rice varieties. The soil hydrochloric acid extracted sulfur content of rice OSC and OSJ increased16.82%,11.77%, respectively. Pyrite content decreased13.1%,13.78%, respectively. Organic sulfur content decreased21.5%,25.3%, respectively. Total sulfur content decreased13.25%,14.47%, respectively. Total Cd content decreased8.43%,10.8%, respectively. Available Cd content decreased3.53%,3.08%, respectively. There was no significant relationship with root distance in root compartments (S0, S1, S2, S3, S4, S5, B) of sulfur forms and Cd.(2) There was significant difference for sulfur and Cd distribution in roots and stems of the two rice varieties. The distribution of sulfur was stems>roots>grains, and the distribution of Cd was roots>stems>grains, the sulfur and Cd accumulation of rice OSC in stems was more than that of rice OSJ, and it was opposite in roots, the Cd accumulation of rice OSC in grains was two times of rice OSJ.(3) The soil available Cd content of rice OSC had very significant positive correlation with pyrite, organic sulfur and total sulfur contents in soils (P=0.005<0.01). The soil total Cd contents of rice OSJ had very significant correlation with hydrochloric acid extracted sulfur, pyrite, organic sulfur and total sulfur contents (P=0.002<0.01). The Cd contents of two rice in stems had significant correlation with sulfur and Cd contents in roots (P<0.05). The Cd contents in grains also had very significant positive correlation with sulfur contents in grains (P<0.01).(4) The capacity of two rice varieties absorbing Cd in stems and roots was affected by various forms of sulfur, Cd and rice varieties. The capacity of two rice accumulating Cd in stems and grains and accumulating S in grains had very significant correlation with pyrite, organic sulfur and total sulfur contents in soils (P <0.01). The Cd and S contents of rice OSC in grains had very significant correlation with available Cd contents (P<0.01), and that of rice OSJ had very significant correlation with total Cd contents (P<0.01). The Cd accumulation in roots of two rice was inhibited by various soil sulfur and promoted by soil Cd content.(5) Urease, acid phosphatase and hydrogen peroxidase of rhizophere soils were remarkably affected by rice varieties, growth period and root system in multi-metal contaminated mining area. Hydrogen peroxidase in soils of the two rice had significant correlation with hydrochloric acid extracted sulfur, total Cd in soils (P<0.05). The soil urease of rice OSC had significant correlation with hydrochloric acid extracted sulfur and acid phosphatase in soils (P<0.05). The soil acid phosphatase and hydrogen peroxidase of rice OSJ had very significant correlation with various sulfur forms and total Cd in soils (P=0.000<0.01).