Agglomeration Determines Effects of Carbonaceous Nanomaterials on Soybean Nodulation, Dinitrogen Fixation Potential, and Growth in Soil

Abstract

The potential effects of carbonaceous nanomaterials (CNMs) on agricultural plants are of concern. However, little research has been performed using plants cultivated to maturity in soils contaminated with various CNMs at different concentrations. Here, we grew soybean for 39 days to seed production in soil amended with 0.1, 100, or 1000 mg kg of either multiwalled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs), or carbon black (CB) and studied plant growth, nodulation, and dinitrogen (N) fixation potential. Plants in all CNM treatments flowered earlier (producing 60% to 372% more flowers when reproduction started) than the unamended controls. The low MWCNT-treated plants were shorter (by 15%) with slower leaf cover expansion (by 26%) and less final leaf area (by 24%) than the controls. Nodulation and N fixation potential appeared negatively impacted by CNMs, with stronger effects at lower CNM concentrations. All CNM treatments reduced the whole-plant N fixation potential, with the highest reductions (by over 91%) in the low and medium CB and the low MWCNT treatments. CB and GNPs appeared to accumulate inside nodules as observed by transmission electron microscopy. CNM dispersal in aqueous soil extracts was studied to explain the inverse dose-response relationships, showing that CNMs at higher concentrations were more agglomerated (over 90% CNMs settled as agglomerates >3 μm after 12 h) and therefore proportionally less bioavailable. Overall, our findings suggest that lower concentrations of CNMs in soils could be more impactful to leguminous N fixation, owing to greater CNM dispersal and therefore increased bioavailability at lower concentrations.

Multiwall Carbon Nanotubes Induce More Pronounced Transcriptomic Responses in Pseudomonas aeruginosa PG201 than Graphene, Exfoliated Boron Nitride, or Carbon Black

“…13 In addition, MWCNTs were shown to have a stronger inhibitory effect on soybean root nodule development than GNPs or CB applied to soil at the same concentration. 7 Since nodules are colonized by symbiotic bacteria to enable N 2 -fixation, inhibited nodule development could have been, as proposed by the authors, an indication of MWCNT effects on N 2 -fixing bacteria. Our results clearly indicate that MWCNTs are more potent at inducing transcriptional changes in bacteria than other types of carbonaceous NMs such as GNPs and CB, but also 2D BN.…”

“…4 Thus, environmental exposures to biota will occur, particularly to bacteria which are environmentally ubiquitous including in soils. 5,6 Generally, NMs could alter bacterial physiology and associated nutrient cycling metabolisms, induce microbial community shifts, 5 and affect plant-microbe interactions; 7 bacteria could also physically affect NM partitioning in environmental compartments and could promote NM exposure to higher organisms by initiating trophic transfer. 6,8 For these reasons, mechanisms of bacterial interactions with carbonaceous and BN NMs should be understood.…”

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

“…[17,18] Similarly, when soybeans were grown in soil amended with carbonaceous nanomaterials (CNMs), multiwall carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs), or carbon black (CB), each dosed at 0.0001, 0.1, or 1 g kg −1 soil, the plants displayed reduced per plant N 2 fixation potentials. [19] Interestingly, CNMs induced more pronounced effects on soybeans at lower CNM concentrations. This phenomenon outlines the unique toxicological profiles of ENMs, which, as particulate materials, tend to agglomerate in environmental matrices, especially at high concentrations.…”

“…[20] As above, ENMs of different physicochemical properties, e.g., metal-based ENMs such as CeO 2 and CNMs such as MWCNTs, GNPs, and CB, have been shown to affect belowground plant tissue and symbiotic N 2 -fixing potential in soybeans. [19,21] However, it is unclear if the effects are caused by ENM damage to plants, rhizobia, or the signaling pathways between plants and symbiotic bacteria. 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.…”

A non-classical route of efficient plant uptake verified with fluorescent nanoparticles and root adhesion forces investigated using AFM

“…Furthermore, NPs loaded with the chemical active ingredients have also extended the scope of microsurgery in plants through triggered release [7][8][9]. To understand the physiological consequences [10][11][12], a comparison of the vascular uptake of NPs was carried out. Interestingly, some aquatic plants showed greater uptake of NPs than ions [13].…”