Variable impact of rice (Oryza sativa) on soil metal reduction and availability of pore water Fe2+ and Mn2+ throughout the growth period

Flooding of wetland or agricultural soils can result in substantial alteration of the pore water trace metal profiles and potentially also influence the bioavailability of other trace elements adsorbed to the insoluble oxides. Experimental microcosms were used to quantify the impact of rice (Oryza sativa) plants across an entire growing cycle on the concentrations of Mn2+ and Fe2+ in two soil types (red sodosol and grey vertosol). Two water management treatments were included: a standard flooded treatment and a saturated treatment (-3 kPa). Soil pore water profiles were established from samples collected at four sampling depths (2.5, 7.5, 15 and 25 cm) on 50 occasions. Fe2+ and Mn2+ concentrations were higher in flooded soil than in saturated soil and greatest at a depth of 7.5 cm. The presence of rice plants increased Mn2+ concentrations in flooded soils, but tended to decrease Mn2+ concentrations in saturated soils. The influence of rice plants on Fe2+ concentrations was greatest at a depth of 7.5 cm. Changes in soil pore water Fe2+ and Mn2+ concentrations due to the presence of rice plants were correlated with flowering and reproduction.