Purpose

Arsenic (As) cycling in flooded rice paddies is driven by soil microbes which among other transformations can cause conversion between inorganic and organic As species. Silicon (Si)-rich soil amendments cause increased methylated As species, particularly DMA, in grain likely because they influence the microbial community responsible for As methylation, but the mechanism remains unclear.

Methods

To investigate how Si-rich amendments influenced the microbial community, we sequenced the 16S rRNA and arsM genes from rhizosphere soil collected at grain ripening from unamended rice paddy mesocosms or those amended with Si-rich rice husk, charred husk, or calcium silicate, and paired these data with geochemistry and As speciation in grain.

Results

We found that Si amendments influenced the 16S rRNA and arsM community composition. Increased C storage from calcium silicate amendment drove differences in the 16S rRNA community, whereas low soil redox potential drove differences in the arsM community. Differences in grain As were observed independent of Si-rich amendments, and did not correspond to differences in either the 16S rRNA or arsM community. Instead, methane flux and soil redox potential correlated with differences in grain DMA.

Conclusions

Si-rich amendments drove changes in the microbial community composition and the subset of arsM-bearing organisms, but higher grain DMA levels were not directly caused by Si-rich amendments. Our findings imply that microbes active at lower soil redox potentials where As is mobilized are likely involved in DMA production, and future work should focus on linking the active community with DMA production.

中文翻译：

---

富硅土壤改良剂影响微生物群落组成和含 arsM 微生物的组成

目的

淹水稻田中的砷 (As) 循环是由土壤微生物驱动的，土壤微生物可导致无机砷和有机砷物种之间的转化。富含硅 (Si) 的土壤改良剂导致谷物中甲基化 As 物种增加，尤其是 DMA，可能是因为它们影响了负责 As 甲基化的微生物群落，但机制尚不清楚。

方法

为了研究富含硅的改良剂如何影响微生物群落，我们对从未改良的稻田中胚层或用富硅稻壳、烧焦的稻壳或硅酸钙改良的稻谷成熟时收集的根际土壤中的 16S rRNA 和arsM基因进行了测序，并将这些数据与地球化学和谷物中的 As 物种形成配对。

结果

我们发现 Si 修正影响了 16S rRNA 和arsM群落组成。来自硅酸钙修正剂的 C 储存增加推动了 16S rRNA 群落的差异，而低土壤氧化还原电位推动了arsM群落的差异。观察到的谷物 As 的差异与富含硅的修正无关，并且不对应于 16S rRNA 或arsM群落的差异。相反，甲烷通量和土壤氧化还原电位与谷物 DMA 的差异相关。

结论

富硅改良剂推动了微生物群落组成和含arsM生物亚群的变化，但较高的谷物 DMA 水平并不是由富硅改良剂直接引起的。我们的研究结果表明，在 As 被动员的较低土壤氧化还原电位下活跃的微生物可能参与 DMA 生产，未来的工作应侧重于将活跃社区与 DMA 生产联系起来。