Silicon enhanced phytoextraction of Sedum alfredii Hance by improving growth, Cd tolerance, and remolding rhizospheric properties

Silicon (Si) has been shown to alleviate cadmium (Cd) toxicity in plants, but the effect of Si on hyperaccumulators such as S. alfredii has not been fully elucidated. This study evaluated the impact of exogenous Si on growth, Cd accumulation, and rhizosphere properties of S. alfredii.

Si was applied to S. alfredii and various parameters were assessed, including biomass, shoot Cd content, chlorophyll, carotenoid levels, malondialdehyde (MDA) content, antioxidant enzyme activity, cell wall composition, soil nutrient availability, and rhizosphere enzyme activities. A thorough transcriptomic analysis was also conducted.

Si significantly increased shoot biomass (21.47–104.35%) and Cd accumulation (144.60–747.11%) in S. alfredii. Si also enhanced chlorophyll levels, reduced the malondialdehyde (MDA) content, increased antioxidant enzyme activities, and mitigated Cd-induced oxidative stress. Si boosted cell wall components, thereby facilitating Cd transport in roots. In rhizosphere soil, Si improved alkaline hydrolysis of nitrogen (AHN), available phosphorus (AP), available potassium (AK), dissolved organic carbon (DOC), and increased available Cd content. Si enhanced rhizospheric enzyme activities. Positive correlations were observed between rhizosphere nutrient availability and plant biomass, enzyme activities and Cd accumulation. Transcriptome analysis showed a higher expression of stress responsive transcription factors (WRKY, basic leucine zipper (bZIP), MYB, NAC) and genes encoding functions involved in metal transport (Heavy Metal ATPases (HMA), Copper Transporter (COPT), chelation (Phytochelatins (PCs), Metallothioneins (MTs), Glutathione (GSH)), and cell wall biosynthesis (Cellulose synthases (Ces), Pectin Methylesterases (PME)).

Si enhanced the tolerance and accumulation of Cd in S. alfredii, underscoring its potential in phytoextraction applications.