College of Resources and Environmental Science, Hunan Normal University, Changsha, Hunan, 410081, China.
College of Resources and Environmental Science, Hunan Normal University, Changsha, Hunan, 410081, China; Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA, 01003, United States.
Environ Pollut. 2018 Dec;243(Pt B):1015-1025. doi: 10.1016/j.envpol.2018.09.054. Epub 2018 Sep 18.
Inhibition of reductive transformation of arsenic (As) in flooded paddy soils is of fundamental importance for mitigating As transfer into food chain. Anaerobic arsenite (As(III)) oxidizers maintain As in less mobile fraction under nitrate-reducing conditions. In this study, we explored the dynamic profile of As speciation in porewater and As distribution among the pools of differential bioavailability in soil solid phase with and without nitrate treatment. In parallel, the abundance and diversity of As(III) oxidase gene (aioA) in flooded paddy soil with nitrate amendment was examined by quantitative PCR and aioA gene clone library. Furthermore, the impact of nitrate on As accumulation and speciation in rice seedlings was unraveled. With nitrate addition (25 mmol NO kg soil), porewater As(III) was maintained at a consistently negligible concentration in the flooded paddy soil and the reductive dissolution of As-bearing Fe oxides/hydroxides was significantly restrained. Specifically, nitrate amendment kept 81% of total soil As in the nonlabile fraction with arsenate (As(V)) dominating after 30 days of flooding, compared to only 61% in the unamended control. Nitrate treatment induced 4-fold higher abundance of aioA gene, which belonged to domains of bacteria and archaea under the classes α-Proteobacteria (6%), ß-Proteobacteria (90%), ɣ-Proteobacteria (2%), and Thermoprotei (2%). By nitrate addition, As accumulation in rice seedlings was decreased by 85% with simultaneously elevated As(V) ratio in rice plant relative to control after 22 days of growth under flooded conditions. These results highlight that nitrate application can serve an efficient method to inhibit reductive dissolution of As in flooded paddy soils, and hence diminish As uptake by rice under anaerobic growing conditions.
在淹水稻田中抑制砷（As）的还原转化对于减轻 As 向食物链中的转移至关重要。在硝酸盐还原条件下，厌氧亚砷酸盐（As(III)）氧化剂将 As 保持在较少移动的部分。在这项研究中，我们探索了有和没有硝酸盐处理时，孔隙水中 As 形态的动态特征以及土壤固相中不同生物有效性池之间的 As 分布。同时，通过定量 PCR 和 aioA 基因克隆文库研究了淹水稻土中硝酸盐添加对 aioA 基因（aioA）丰度和多样性的影响。此外，还揭示了硝酸盐对水稻幼苗中 As 积累和形态的影响。添加硝酸盐（25 mmol NO kg 土壤）后，淹水稻土中的孔隙水 As(III)保持在可忽略不计的浓度，含 As 的铁氧化物/氢氧化物的还原溶解受到显著抑制。具体而言，与未添加硝酸盐的对照相比，硝酸盐添加将 81%的总土壤 As 保持在稳定的非活性部分，其中砷酸盐（As(V)）占主导地位，而在未添加硝酸盐的对照中，只有 61%的总土壤 As 保持在非活性部分。硝酸盐处理诱导 aioA 基因的丰度增加了 4 倍，该基因属于细菌和古菌的 α-变形菌（6%）、β-变形菌（90%）、γ-变形菌（2%）和 Thermoprotei（2%）。通过添加硝酸盐，在淹水条件下生长 22 天后，与对照相比，水稻幼苗中 As 的积累减少了 85%，而水稻植株中 As(V)的比例增加。这些结果表明，硝酸盐的应用可以有效地抑制淹水稻土中 As 的还原溶解，从而减少在厌氧生长条件下水稻对 As 的吸收。
