Si-induced DMA desorption is not the driver for enhanced DMA availability after Si addition to flooded soils

Dykes, Gretchen E.; Chari, Nikhil R.; Seyfferth, Angelia L.

doi:10.1016/j.scitotenv.2020.139906

Cited by 15 publications

(9 citation statements)

References 44 publications

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“…Increased porewater Si from husk amendment can decrease rice uptake of arsenite, but Si can also increase accumulation of DMA in rice grain 11 , 16 , despite DMA entering rice roots through the silicon channel Lsi1 and hydroponic work demonstrating Si can decrease grain concentrations of DMA 9 , 51 . Exogenous Si leads to increased microbial methylation of As likely due to Si-induced desorption of inorganic As and consequent methylation 23 . This results in more DMA available for plant-uptake upon Si-rich husk amendment.…”

Section: Discussionmentioning

confidence: 99%

“…Unfortunately most increases in grain DMA result from increases in plant exposure to As through As-contaminated soil or soil amendments that substantially decrease the soil redox thereby increasing As availability through reductive dissolution 11 . Silicon addition to the soil via husk amendment can increase As methylation 23 , but ideal Si-rich amendments must provide limited labile carbon to prevent undesirable decreases in soil redox potential that risk increasing total As. For these reasons, we recommend rice husk instead of rice straw 65 .…”

Section: Discussionmentioning

confidence: 99%

“…Because arsenite enters rice roots through Si transporters 16 , increased plant-available Si decreases inorganic As in rice grain 11 , 17 – 21 . However, increased plant-available Si can increase grain organic As, likely through Si-induced desorption of arsenite in the porewater 22 leading to increased microbial methylation 11 , 23 . Despite a growing body of literature on the factors that affect grain As concentration and speciation, few studies investigate factors that affect the localization of As in grain.…”

Section: Introductionmentioning

confidence: 99%

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Altering the localization and toxicity of arsenic in rice grain

Limmer

Seyfferth

2022

Sci Rep

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Previous work has shown that inorganic As localizes in rice bran whereas DMA localizes in the endosperm, but less is known about co-localization of As and S species and how they are affected by growing conditions. We used high-resolution synchrotron X-ray fluorescence imaging to image As and S species in rice grain from plants grown to maturity in soil (field and pot) and hydroponically (DMA or arsenite dosed) at field-relevant As concentrations. In hydroponics, arsenite was localized in the ovular vascular trace (OVT) and the bran while DMA permeated the endosperm and was absent from the OVT in all grains analyzed, and As species had no affect on S species. In pot studies, soil amended with Si-rich rice husk with higher DMA shifted grain As into the endosperm for both japonica and indica ecotypes. In field-grown rice from low-As soil, As localized in the OVT as arsenite glutathione, arsenite, and DMA. Results support a circumferential model of grain filling for arsenite and DMA and show Si-rich soil amendments alter grain As localization, potentially lessening risk to rice consumers.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Altering the localization and toxicity of arsenic in rice grain

Limmer

Seyfferth

2022

Sci Rep

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“…Silicic acid can desorb arsenous acid (arsenite) due to the chemical similarity between these two compounds (Luxton et al., 2006). This Si‐driven desorption of arsenite is coincident with elevated As o concentrations early in the growing season, likely due to higher arsenite concentrations driving microbial methylation of arsenite to DMA and TMAO (Challenger, 1945; Dykes et al., 2020; Seyfferth et al., 2018; Zhao et al., 2013). Except for Char, Si‐rich treatments maintained constant, elevated levels of As o in the porewater throughout the experiment.…”

Section: Discussionmentioning

confidence: 99%

“…Hypotheses for these results have included Si‐induced desorption of either arsenite (Luxton et al., 2006) or DMA (Liu et al., 2014) with the former leading to enhanced biomethylation rates in the soil (Seyfferth et al., 2018). Recent research suggests that Si‐induced desorption of arsenite is the primary cause (Dykes et al., 2020). The interactions between Si, arsenite, and DMA in both the soil and in the plant have made understanding underlying mechanisms difficult.…”

Section: Introductionmentioning

confidence: 99%

Carryover effects of silicon‐rich amendments in rice paddies

Limmer

Seyfferth

2021

Soil Science Soc of Amer J

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Rice (Oryza sativa L.) readily accumulates the nutrient silicon (Si) and the toxin arsenic (As), elements that can interact antagonistically both in the plant and in the soil. Thus, many studies have been performed where Si‐rich materials are incorporated into soils to increase plant‐available Si and thereby decrease plant As. However, studies have not examined the dissolution kinetics of Si from Si‐rich materials over multiple seasons and the resulting effects on rice systems. Here, we analyzed the porewater chemistry, CH4 emissions, and rice elemental concentrations from rice paddies in Year 2 that had been amended with Si‐rich materials (silicate fertilizer, rice husk, and charred rice husk) in Year 1. After two crop cycles, plant‐available Si and plant Si concentrations remained elevated in Si‐amended paddies. Silicon‐rich amendments also decreased plant As concentrations, although this effect was only observed in the vegetative tissues. Husk treatment resulted in the lowest porewater redox, highest CH4 emissions, and highest porewater inorganic As. Porewater concentrations and dynamics of inorganic As, dimethylarsinic acid (DMA), and trimethylarsine oxide (TMAO) differed for each amendment, but Si‐rich amendments exhibited elevated inorganic and organic As early in the growing season. These Si‐rich amendments can continue to provide Si and impact rice systems two growing seasons after application.

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Silicon-rich soil amendments impact microbial community composition and the composition of arsM bearing microbes

2021

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Purpose: Arsenic (As) cycling in ooded 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 in uence the microbial community responsible for As methylation, but the mechanism remains unclear.Methods: To investigate how Si-rich amendments in uenced 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 in uenced the 16S and arsM community composition. Increased C storage from calcium silicate amendment drove differences in the 16S community, whereas low redox from husk amendments drove differences in the arsM community. High grain DMA was not associated with treatment or microbial community, but with low redox.Conclusions: Differences in grain As were observed independent of amendments, and did not correspond to differences in either the 16S or arsM community. Instead, methane ux and redox correlated with differences in grain DMA, implying that methanogen activity and redox are more important factors than community composition in determining grain As speciation. Silicon amendments did not impact grain As, but impacted the microbial community composition, and the subset of arsM-bearing organisms. These ndings imply that redox, porewater As, and methanogen activity are likely more important factors than arsM or overall microbial community composition in determining grain DMA levels.

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Si-induced DMA desorption is not the driver for enhanced DMA availability after Si addition to flooded soils

Cited by 15 publications

References 44 publications

Altering the localization and toxicity of arsenic in rice grain

Altering the localization and toxicity of arsenic in rice grain

Carryover effects of silicon‐rich amendments in rice paddies

Silicon-rich soil amendments impact microbial community composition and the composition of arsM bearing microbes

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