Sulfur and water management mediated iron plaque and rhizosphere microorganisms reduced cadmium accumulation in rice

PurposeCadmium (Cd) accumulation in rice can be regulated by applying sulfur (S) fertilizers and water management, but the mechanism and the effect on soil microorganisms are unclear. This study aims to clarify the effect of sulfur forms on rice Cd accumulation and soil microbial community structure under different irrigation regimes.MethodsThe present study investigated the effects of sulfur fertilizers (S-0 and Na2SO4) and water management by continuous flooding (flooded) and intermittent flooding and draining (Int-F3D5) on soil Cd bioavailability and the microbial community structure using inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS), and 16S rRNA gene sequencing technology.ResultsWhen flooded, S-0 and Na2SO4 increased the dry weight of rice grain 2.3- and 0.9-fold, respectively, and reduced the Cd concentration by 152% and 61%, respectively. The ascorbic citrate acetic (ACA) extractable Fe content from flooded rice surface treated with S-0 and Na2SO4 increased by 98% and 64%, respectively, indicating that the S fertilizer promoted iron plaque formation on the surfaces of rice roots. Gammaproteobacteria were the most predominant under all management conditions. Syntrophobacteraceae and Geobacter were particularly abundant in the rice rhizosphere treated with Int-F3D5 and exogenous Na2SO4, and it might play a crucial role in alleviating Cd stress caused by S fertilizer.ConclusionUnder flooded conditions, S-0 had a more significant effect on the reduction of cadmium uptake by rice. Sulfur fertilizers promoted iron plaque formation partially to hinder Cd accumulation. Under Int-F3D5 conditions, Na2SO4 recruited more beneficial rhizosphere bacteria, which may be a potential mechanism of reducing Cd transfer from soil to rice.

Automated summary

This study aimed to investigate the effects of different sulfur fertilizers on rice cadmium accumulation and soil microbial community structure under different irrigation conditions. The results showed that sulfur fertilizers had a significant impact on rice cadmium accumulation and soil microbial community structure under continuous flooding and intermittent flooding and draining conditions.