Soil sulfide accumulation and stress mitigation of S. alterniflora by radial oxygen loss and iron enrichment in rhizosphere

Background and Aims Spartina alterniflora ( S. alterniflora ) is an invasive plant widely distributed in coastal areas of China, and the invasion has caused the accumulation of soil sulfur contents, while sulfide can accumulate to phytotoxic levels. It has been verified that S. alterniflora is more tolerant to sulfide than Scirpus mariqueter ( S. mariqueter ). Therefore, sulfide may play an important role in invading S. alterniflora , but the specific mechanism awaits further investigation. Methods Through experiments with situ rhizoboxes in the Jiuduansha Wetland, we conducted field investigations to analyze soil sulfur (sulfate and sulfide) contents, iron (Fe(II) and Fe(III)) contents, and physicochemical properties. Lab-scale experiment with high-resolution (HR) diffusive gradients in thin films (DGT) was conducted to investigate the distribution of oxygen, sulfide, and iron concentrations in the microenvironment of two species. Meanwhile, the effect of roots on soil bacterial communities and sulfur cycle-related microorganisms was investigated. Results The soil sulfur (sulfide and sulfate) contents in S. alterniflora were higher than in S. mariqueter . In the rhizoboxes of S. alterniflora , the contents of soil sulfide were significantly lower in the rhizosphere, while oxygen contents in the rhizosphere were higher than in bulk soil. The iron contents in S. alterniflora were significantly higher than in S. mariqueter , especially the Fe(III) contents were higher in the rhizosphere. Conclusion The S. alterniflora may gain an advantage in the invasion process by oxidizing the sulfide through radial oxygen loss and by enriching iron to mitigate high concentrations of sulfide in the rhizosphere.