ARS | Publication request: Microbial dynamics and arsenic speciation in rice paddy soil under two water management practices

Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2009
Publication Date: February 20, 2009
Citation: Somenahally, A., Loeppert, R., Yan, W., Gentry, T. 2009. Microbial dynamics and arsenic speciation in rice paddy soil under two water management practices [abstract]. 109th American Society for Microbiology Annual Meeting. Paper No. Q-044.

Technical Abstract: Arsenic (As) undergoes several microbial transformations, including oxidation/reduction, methylation/demethylation, and volatilization in soil, which impact As bioavailability. Different water management systems for rice cultivation alter soil-redox conditions and As biogeochemistry. Soil microbial communities and arsenic speciation were studied in a factorial experiment with two As levels, native paddy and addition of monosodium methanearsonate (MSMA), and two water practices, continuous and intermittent flooding at Stuttgart, AR in 2008. Soil samples were collected at different intervals and their microbial communities examined using whole soil fatty acid methyl ester (FAME) analysis along with PCR amplification of genes encoding arsenate reductase (arsC) and dissimilatory arsenate reductase (arrA). Organic and inorganic-As species in soil and pore-water samples were extracted and determined by HPLC-ICP-MS. The FAME data indicated large differences in microbial community composition as impacted by both As and water-management treatments. The microbial communities were more diverse in low As native soils than in MSMA-amended soils and in intermittently flooded soils compared to continuously flooded soils. The fungi:bacteria ratios decreased over time as bacterial populations increased and fungal populations decreased upon continuous flooding. Higher soil-As concentrations altered bacterial populations but not fungal populations. Neither arrA nor arsC were detected in any of the samples. Inorganic and organic-As species were significantly higher in continuously flooded treatments with AsIII being the predominant form in pore-water samples. Methyl As compounds including dimethyl-arsinic acid were only detected in the MSMA-amended, continuously flooded treatments. Therefore, increased soil microbial diversity and bacterial populations and decreased organic and inorganic As in pore water were achieved by the intermittently flooding practice.