Active Silicon-Impeded Arsenic Accumulation in Rice and Reshaped Rhizosphere Microbial Communities Enabled by Novel Rice Husk Ash

Arsenic (As) contamination in paddy soils is a widespread environmental concern that threatens rice safety and human health. Although silicon (Si) effectively suppresses As accumulation in rice through the shared transport pathway mediated by OsLsi1 and OsLsi2, currently available Si amendments are limited by high cost, the potential risk of As remobilization, and short-term Si-supplying capacity. In this study, a novel silicon-rich rice husk ash (Si-RHA) was developed to mitigate As accumulation in rice while reshaping rhizosphere microbial communities potentially associated with As immobilization. Compared with CK, Si-RHA reduced brown rice As concentration by 55.9% and increased Si concentration by 60.2%, outperforming conventional rice husk ash (RHA) and commercial water-soluble Si fertilizer (GF). This superior performance was associated with a 109.8% increase in porewater Si concentration, a 528.6% increase in Si accumulation within root iron plaque, and a 122.0% increase in soil available Si, accompanied by a 47.8% decrease in the non-specifically sorbed As fraction. High-throughput sequencing of the silA functional gene further showed that Si-RHA reshaped silA-associated microbial communities, increasing microbial diversity (Shannon index, +7.9%) and enriching Geobacter-associated functional assemblages potentially involved in Fe cycling and As immobilization, whereas GF markedly reduced microbial diversity (Shannon index, -31.6%). This study provides a value-added Si-rich amendment derived from rice husk ash for mitigating As contamination in paddy soils.