Influence of elemental sulfur on cadmium bioavailability, microbial community in paddy soil and Cd accumulation in rice plants

Abstract

Cadmium (Cd) is highly toxic to living organisms and the contamination of Cd in paddy soil in China has received much attention. In the present study, by conducting pot experiment, the influence of S fertilizer (S0) on rice growth, iron plaque formation, Cd accumulation in rice plants and bacterial community in rice rhizosphere soil was investigated. The biomass of rice plants was significantly increased by S0 addition (19.5–73.6%). The addition of S0 increased the formation of iron plaque by 24.3–45.8%, meanwhile the amount of Cd sequestered on iron plaque increased. In soil treated with 5 mg/kg Cd, addition of 0.2 g/kg S0 decreased the diffusive gradients in thin films (DGT) extractable Cd by 60.0%. The application of S0 significantly decreased the concentration of Cd in rice grain by 12.1% (0.1 g/kg) and 36.6% (0.2 g/kg) respectively. The addition of S0 significantly increased the ratio of Acidobacteria, Bacteroidetes in rice rhizosphere soil. Meanwhile, the ratio of Planctomycetes and Chloroflexi decreased. The results indicated that promoting Fe- and S-reducing and residue decomposition bacterial in the rhizosphere by S0 may be one biological reason for reducing Cd risk in the soil-rice system.

Effects of sulfur supply on cadmium transfer and concentration in rice at different growth stages exposed to sulfur-deficient but highly cadmium-contaminated soil

“…In the present study, the application of S (30 mg S kg −1 ) in Cd-contaminated (available S of 16.5 mg kg −1 , total Cd of 10.16 mg kg −1 ) soil significantly increased the rice grain biomass although it had no obvious effect on the root, leaf and stem biomass (Table 1), implying that the application of S could improve rice grain biomass under high Cd stress and S-deficient. The current results are consistent with those reported by [9,12]. This is because the application of S in S-deficient soils provided sulfur for rice growth and development.…”

“…Previous studies reported that excess S supply (60-300 mg S kg −1 ) in moderately Cd-contaminated soils (3.72 and 5 mg Cd kg −1 ) increased rice biomass [8,13]. Similarly, the application of S in low Cd-contaminated (0.79 and 1.5 mg Cd kg −1 ) and low S-containing soils also increased rice biomass [9,12]. However, the application of S in Cd-contaminated (2.22 mg Cd kg −1 ) but high S-containing (797 mg S kg −1 ) soil reduced rice biomass [8].…”

“…However, excessive S supply (60-300 mg S kg −1 ) in moderately Cd-contaminated soils (3.72 and 5 mg Cd kg −1 ) was reported to increase the biomass of rice [8,13]. Similarly, the application of S in low Cd-contaminated (0.79 and 1.5 mg Cd kg −1 ) and low S soils was also observed to increase rice biomass [9,12]. In the present study, the application of S (30 mg S kg −1 ) in Cd-contaminated (available S of 16.5 mg kg −1 , total Cd of 10.16 mg kg −1 ) soil significantly increased the rice grain biomass although it had no obvious effect on the root, leaf and stem biomass (Table 1), implying that the application of S could improve rice grain biomass under high Cd stress and S-deficient.…”

“…Second, the existing effects of S application on the concentration of Cd in rice vary widely and even conflict, which is related to soil S levels. Previous studies have shown that the application of S in low S-containing (total S < 200 mg kg −1 , or Ca (H 2 PO 4 ) 2 extractable S < 26.7 mg kg −1 ) soils significantly reduced the concentration of Cd in rice plants [9,10,12,13]. However, Zhang et al [15] observed that the application of S (114-458 mg S kg −1 ) in S-rich soils increased the concentrations of Cd in roots, stems, leaves and grains.…”

“…Sulfur (S) is an essential nutrient for plant growth and acts as a resistance factor against biotic and abiotic stress in plants [7]. S has been widely used to alleviate Cd toxicity and control the accumulation of Cd in rice under waterlogging conditions [1,[8][9][10][11][12][13][14], but the existing results of Cd transfer and accumulation in rice vary widely and even conflicting [15][16][17][18]. First, the existing effects of S application on rice biomass vary widely and even conflicting, which are related to the degree of soil Cd contamination and soil S levels.…”