Influence of water management on the active root-associated microbiota involved in arsenic, iron, and sulfur cycles in rice paddies

Abstract

In recent years, the role of microorganisms inhabiting rice rhizosphere in promoting arsenic contamination has emerged. However, little is known concerning the species and metabolic properties involved in this phenomenon. In this study, the influence of water management on the rhizosphere microbiota in relation to arsenic dissolution in soil solution was tested. Rice plants were cultivated in macrocosms under different water regimes: continuous flooding, continuous flooding with a 2-week period drainage before flowering, and dry soil watered every 10 days. The active bacterial communities in rhizosphere soil and in rhizoplane were characterized by 16S rRNA pyrosequencing. An in-depth analysis of microbial taxa with direct or indirect effects on arsenic speciation was performed and related contribution was evaluated. Continuous flooding promoted high diversity in the rhizosphere, with the plant strongly determining species richness and evenness. On the contrary, under watering the communities were uniform, with little differences between rhizosphere soil and rhizoplane. Arsenic-releasing and arsenite-methylating bacteria were selected by continuous flooding, where they represented 8% of the total. On the contrary, bacteria decreasing arsenic solubility were more abundant under watering, with relative abundance of 10%. These values reflected arsenic concentrations in soil solution: 135 μg L and negligible in continuous flooding and under watering, respectively. When short-term drainage was applied before flowering, intermediate conditions were achieved. This evidence strongly indicates an active role of the rhizosphere microbiota in driving arsenic biogeochemistry in rice paddies, influenced by water management, explaining amounts and speciation of arsenic often found in rice grains.

Arsenic concentrations and speciation in Australian and imported rice and commercial rice products

“…Rice from these areas contains elevated DMA concentrations, which account for up to 80 % of the total As content (Heitkemper et al 2001;Williams et al 2006). The methylation of As within rice has not been documented; thus, DMA is probably accumulated by plants from soils where bacteria have methylated inorganic As (Lomax et al 2012;Zecchin et al 2017a). High DMA concentrations found in rice could also be attributed to agronomic practices.…”

“…For example, As within aerobically grown rice is typically found as inorganic As whereas in rice from flooded fields with low oxygen concentrations, the major As species was DMA (Xu et al 2008). Flooding tends to reduce oxygen concentrations and hence promotes DMA production (Turpeinen et al 2002;Zecchin et al 2017a). Accumulation, however, may also depend on the cultivar (Kuramata et al 2013;Lemos Batista et al 2014).…”

Soil Bacterial Community Associated With High Potato Production and Minimal Water Use

“…The soil has been classified as one of the most diverse ecosystems on Earth (Thompson et al, 2017). It has been verified that the microbial community plays an essential role in the soil environment system; that is acting on the biogeochemical cycles, such as those of nitrogen (Prosser and Nicol, 2008), sulfur (Zecchin et al, 2017), and carbon (Meyer et al, 2017). The soil microbial community also plays significant roles in plant nutrition.…”

Bacteria Responsible for Nitrate-dependent Antimonite Oxidation in Antimony-contaminated Paddy Soil Revealed by the Combination of DNA-SIP and Metagenomics

“…Many bins, such as those associated with Thauera, Ramlibacter and Anaeromyxobacter, contained an aioA gene. Although Thauera, Ramlibacter and Anaeromyxobacter have been detected in As-contaminated sites previously [45][46][47], their role in either As(III) or Sb(III) oxidation has not been reported. The presence of aioA and the genes responsible for denitri cation and carbon xation in the bins related with these genera (Fig.…”