Microbial Activity Spurred By Silicon Amendment Addition Alters the Biogeochemical Cycling of Arsenic in Flooded Rice Paddies.

Rice is a staple food for approximately half the world. Arsenic (As) accumulation in rice due to arsenite uptake via the rice silicon transporter is an issue in areas where rice is grown in flooded paddies, and especially where irrigation water is arsenic contaminated. One potential arsenic uptake mitigation strategy is use of silicon (Si) amendments such as rice husk, rice husk ash, and calcium silicate; all increase the amount of plant-available Si in the soil, have been shown to decrease inorganic As uptake, and are economically feasible and available for small rice farmers. Although Si amendment use decreases grain inorganic As, increased organic As levels have been observed in grains of rice grown in Si amended soils. This is likely due to spurred arsenic methylating microbe activity. Arsenic methylating microbes convert inorganic arsenic to organic, methylated forms such as monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). The diversity and abundance of arsenic methylating microbes from the rhizosphere were compared across soils treated with rice husk, rice husk ash, and calcium silicate.