Synergistic Effects of Water Management and Silicon Foliar Spraying on the Uptake and Transport Efficiency of Cadmium in Rice (Oryza sativa L.)

Abstract

To study the synergistic effects of water management and silicon (Si) foliar spraying on the uptake and transport of cadmium (Cd) in rice, we designed four treatments: conventional intermittent flooding + no Si foliar spraying (CK), continuous flooding throughout the growth stage + no Si foliar spraying (W), conventional intermittent flooding + Si foliar spraying (Si) and continuous flooding throughout the growth stage + Si foliar spraying (WSi). The results show that WSi treatment reduced the uptake and translocation of Cd by rice and significantly reduced the brown rice Cd content, with no effect on rice yield. Compared with CK, the Si treatment increased the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of rice by 6.5-9.4%, 10.0-16.6% and 2.1-16.8%, respectively. The W treatment decreased these parameters by 20.5-27.9%, 8.6-26.8% and 13.3-23.3%, respectively, and the WSi treatment decreased them by 13.1-21.2%, 3.7-22.3% and 2.2-13.7%, respectively. The superoxide dismutase (SOD) and peroxidase (POD) activity decreased by 6.7-20.6% and 6.5-9.5%, respectively, following the W treatment. Following the Si treatment, SOD and POD activity increased by 10.2-41.1% and 9.3-25.1%, respectively, and following the WSi treatment, they increased by 6.5-18.1% and 2.6-22.4%, respectively. Si foliar spraying ameliorated the detrimental effects of continuous flooding throughout the growth stage on photosynthesis and antioxidant enzyme activity. We conclude that synergistic continuous flooding throughout the growth stage, combined with Si foliar spraying, can significantly block Cd uptake and translocation and is therefore an effective means of reducing the accumulation of Cd in brown rice.

Keywords: Si; cadmium; foliar spraying; photosynthesis; water management.

Figure 1

Synergistic effects of water management and silicon foliar spraying on Cd content of brown rice and rice yield. The histogram and line chart represent Cd content of brown rice and rice yield, respectively. The error bar represents three repeated standard deviations (SD). There is no significant difference between values with the same letters in the table (p ≥ 0.05, Fisher’s LSD test). A, B and C represent the actual measured Cd content in soil after the addition of exogenous Cd at 0.20 mg·kg⁻¹, 0.60 mg·kg⁻¹ and 1.60 mg·kg⁻¹, respectively.

Figure 2

Synergistic effects of water management and silicon foliar spraying on the Cd translocation factor of rice organs ((a) TF_root−stem; (b) TF_stem−leaf; (c) TF_{stem−brown rice}; (d) TF_{leaf−brown rice}). The error bar represents three repeated standard deviations (SDs). There is no significant difference between values with the same letters in the table (p ≥ 0.05, Fisher’s LSD test). A, B and C represent the actual measured Cd content in soil after the addition of exogenous Cd at 0.20 mg·kg⁻¹, 0.60 mg·kg⁻¹ and 1.60 mg·kg⁻¹, respectively.

Figure 3

Synergistic effects of water management and silicon foliar spraying on SPAD values of rice leaves. The error bar represents three repeated standard deviations (SDs). There is no significant difference between values with the same letters in the table (p ≥ 0.05, Fisher’s LSD test). A, B and C represent the actual measured Cd content in soil after the addition of exogenous Cd at 0.20 mg·kg⁻¹, 0.60 mg·kg⁻¹ and 1.60 mg·kg⁻¹, respectively.

Figure 4

Synergistic effects of water management and silicon foliar spraying on rice photosynthesis ((a) net photosynthetic rate (Pn); (b) stomatal conductance (Gs); (c) transpiration rate (Tr); (d) intercellular CO₂ concentration (Ci)). The error bar represents three repeated standard deviations (SDs). There is no significant difference between values with the same letters in the table (p ≥ 0.05, Fisher’s LSD test). A, B and C represent the actual measured Cd content in soil after the addition of exogenous Cd at 0.20 mg·kg⁻¹, 0.60 mg·kg⁻¹ and 1.60 mg·kg⁻¹, respectively.

Figure 5

Radar plots of the synergistic effects of water management and silicon foliar spraying on MDA, SOD and POD contents in rice leaves ((a) malondialdehyde (MDA); (b) superoxide dismutase (SOD); (c) peroxidase (POD)). A, B and C represent the actual measured Cd content in soil after the addition of exogenous Cd at 0.20 mg·kg⁻¹, 0.60 mg·kg⁻¹ and 1.60 mg·kg⁻¹, respectively.

Figure 6

Diagram of the potting experiment ((a) conventional intermittent flooding + no Si foliar spraying (CK); (b) continuous flooding throughout the growth stage + no Si foliar spraying (W); (c) conventional intermittent flooding + Si foliar spraying; (d) continuous flooding throughout the growth stage + Si foliar spraying (WSi)).