Carbonaceous Nanomaterials Have Higher Effects on Soybean Rhizosphere Prokaryotic Communities During the Reproductive Growth Phase than During Vegetative Growth

Abstract

Carbonaceous nanomaterials (CNMs) can affect agricultural soil prokaryotic communities, but how the effects vary with the crop growth stage is unknown. To investigate this, soybean plants were cultivated in soils amended with 0, 0.1, 100, or 1000 mg kg of carbon black, multiwalled carbon nanotubes (MWCNTs), or graphene. Soil prokaryotic communities were analyzed by Illumina sequencing at day 0 and at the soybean vegetative and reproductive stages. The sequencing data were functionally annotated using the functional annotation of prokaryotic taxa (FAPROTAX) database. The prokaryotic communities were unaffected at day 0 and were altered at the plant vegetative stage only by 0.1 mg kg MWCNTs. However, at the reproductive stage, when pods were filling, most treatments (except 1000 mg kg MWCNTs) altered the prokaryotic community composition, including functional groups associated with C, N, and S cycling. The lower doses of CNMs, which were previously shown to be less agglomerated and thus more bioavailable in soil relative to the higher doses, were more effective toward both overall communities and individual functional groups. Taken together, prokaryotic communities in the soybean rhizosphere can be significantly phylogenetically and functionally altered in response to bioavailable CNMs, especially when soybean plants are actively directing resources to seed production.

Limited effects of depth (0–80 cm) on communities of archaea, bacteria and fungi in paddy soil profiles

“…Box plots for significant OTUs were generated using R after Borcard, Gillet, and Legendre (2018). To compare the relative abundances of putative functional bacterial groups between sampling sites or depth intervals, one-way analysis of variance (ANOVA) with a post hoc least significant difference (LSD) test was employed according to Ge et al (2018) using R after Borcard et al (2018).…”

Temporal Changes in the Function of Bacterial Assemblages Associated With Decomposing Earthworms

“…The main limitation of applying FAPROTAX to our data is the implicit assumption in FAPROTAX that if the cultured members of a taxon can perform a particular function, then all members of the taxon (both the cultured and non-cultured) can perform that function ( Ge et al, 2018 ). However, less than 1% of all microbial taxa have been studied in culture.…”

“…However, less than 1% of all microbial taxa have been studied in culture. In this sense, the functional implications of the shifts in bacterial community could be larger than what can be currently inferred using this approach ( Ge et al, 2018 ). With the 16S sequencing approach, we used function-by-proxy to determine the components of the structure–function relationship; however, our ability to parse functional groups is limited.…”

Physical Properties of Carbon Nanomaterials and Nanoceria Affect Pathways Important to the Nodulation Competitiveness of the Symbiotic N2‐Fixing Bacterium Bradyrhizobium diazoefficiens

“…A correlation between the reverse dose relationship and the agglomeration state of MWCNTs was previously established. [19] Specifically, MWCNTs negatively affected soybean nodulation and N 2 fixation potential [19] and significantly altered soil prokaryotic communities, [22] with stronger effects observed for lower MWCNT doses.…”

“…Soybean exposure to CeO 2 NPs and MWCNTs via soil resulted in root nodules that were devoid of bacteroids, [19,21] indicating that symbiotic bacteria were perturbed by ENMs. However, Ge et al [22] found that bacterial populations associated with N 2 fixation were insensitive to CNM treatment in soybean-planted soil. Altogether these results suggest that ENM effects on N 2 -fixing systems may not manifest in the growth inhibition of symbiotic bacteria but rather occur during the initiation of nodulation or symbiosis formation.…”