Selenium Nanoparticles as an Innovative Selenium Fertilizer Exert Less Disturbance to Soil Microorganisms

Abstract

Selenium (Se) is an essential trace element in the human body. Se-enriched agricultural products, obtained by applying Se fertilizer, are important sources of Se supplement. However, Se fertilizer may cause a series of environmental problems. This study investigated the transformation of exogenous selenium nanoparticles (SeNPs) and selenite (SeO₃ ^2-) in soil and explored their effects on soil microbial community and typical microorganisms. SeNPs exhibited a slow-release effect in soil, which promoted the growth of soil microorganisms and enriched soil probiotics. SeO₃ ^2- was converted to a stable and low toxic state in soil, increasing persistent free radicals and decreasing microbial abundance and diversity. The influences of SeNPs and SeO₃ ^2- on two typical soil microorganisms (Bacillus sp. and Escherichia coli) were also evaluated, and SeNPs were more difficult to enter into microorganisms directly, with lower toxicity and higher safety. These results indicated that SeNPs were a more environment-friendly Se additive for agriculture applications. This work provides useful information for better understanding the environmental fate and behavior of Se fertilizer in the soil.

Keywords: environmental persistent free radicals; selenite; selenium fertilizer; selenium nanoparticles; soil microorganism.

FIGURE 1

Variation of soil-available selenium (Se) fractions. (A) High selenium nanoparticles (SeNPs): the samples collected from the group treated with 10 mmol/kg soil SeNPs. (B) High selenite (SeO₃^2–): the samples collected from the group treated with 10 mmol/kg soil SeO₃^2–. (C) Low SeNPs: the samples collected from the group treated with 1 mmol/kg soil SeNPs. (D) Low SeO₃^2–: the samples collected from the group treated with 1 mmol/kg soil SeO₃^2–. Significant differences were analyzed by ANOVA; ^∗∗∗p < 0.001.

FIGURE 2

Abundance and diversity of the microbiota in each experimental group. (A) Total soil bacteria abundance. (B) Shannon Index. (C) Principal coordinates analysis (PCoA) plots of Bray–Curtis distances at the genus level. (D) PCoA plots of weighted UniFrac distances at the genus level. Control: the samples collected from the control group without selenium (Se) treatment. High selenite (SeO₃^2–): the samples collected from the group treated with 10 mmol/kg soil SeO₃^2–. Low SeO₃^2–: the samples collected from the group treated with 1 mmol/kg soil SeO₃^2–. High selenium nanoparticles (SeNPs): the samples collected from the group treated with 10 mmol/kg soil SeNPs. Low SeNPs: the samples collected from the group treated with 1 mmol/kg soil SeNPs. ^∗ in (C,D) shows the data point of untreated soil. Significant differences were analyzed by ANOVA; ^∗∗p < 0.01. Different letters indicate a significant difference (p < 0.05).

FIGURE 3

Taxonomy composition of the microbiota in each experimental group. (A) The relative abundance of major bacteria phyla. (B) The relative abundance of major bacteria genera. (C,D) The top 15 significantly changed genera identified by linear discriminant analysis effect size (LEfSe) on Days 7 (C) and 30 (D). Control: the samples collected from the control group without selenium (Se) treatment. High selenite (SeO₃^2–): the samples collected from the group treated with 10 mmol/kg soil SeO₃^2–. Low SeO₃^2–: the samples collected from the group treated with 1 mmol/kg soil SeO₃^2–. High selenium nanoparticles (SeNPs): the samples collected from the group treated with 10 mmol/kg soil SeNPs. Low SeNPs: the samples collected from the group treated with 1 mmol/kg soil SeNPs.

FIGURE 4

Co-occurrence network analysis showing the biological interactions at the family level under the treatment of selenite (SeO₃^2–) (A) and selenium nanoparticles (SeNPs) (B). The size of the nodes is relative abundance. The scatter plot shows criteria of selecting for the keystone taxa in SeO₃^2– (C) and SeNP (D) networks.

FIGURE 5

Electron paramagnetic resonance (EPR) spectra of each experimental group on Days 7 and 30.

FIGURE 6

Effects of selenium nanoparticles (SeNPs) and selenite (SeO₃^2–) on typical soil microorganisms. (A) OD₆₀₀. (B) Total protein concentration. (C) Glutathione peroxidase (GSH-Px) activity. (D) Reactive oxygen species.