Effects of carbonaceous nanomaterials on soil-grown soybeans under combined heat and insect stresses

Abstract

Environmental contextEngineered nanomaterials have the potential to accumulate in agricultural soils where they may influence crop plants. There is, however, little information about how adverse environmental conditions may interact with nanomaterial effects on plants and plant-microbe interactions. We report the comparative effects of three carbonaceous nanomaterials on the growth, nodulation and foliar health of a globally important legume crop, soybean, under the combined stresses of high temperature and insect pests. AbstractBecause carbonaceous nanomaterials (CNMs) are expected to enter soils, the exposure implications to crop plants and plant–microbe interactions should be understood. Most investigations have been under ideal growth conditions, yet crops commonly experience abiotic and biotic stresses. Little is known how co-exposure to these environmental stresses and CNMs would cause combined effects on plants. We investigated the effects of 1000mgkg−1 multiwalled carbon nanotubes (CNTs), graphene nanoplatelets (GNPs) and industrial carbon black (CB) on soybeans grown to the bean production stage in soil. Following seed sowing, plants became stressed by heat and infested with an insect (thrips). Consequently, all plants had similarly stunted growth, leaf damage, reduced final biomasses and fewer root nodules compared with healthy control soybeans previously grown without heat and thrips stresses. Thus, CNMs did not significantly influence the growth and yield of stressed soybeans, and the previously reported nodulation inhibition by CNMs was not specifically observed here. However, CNMs did significantly alter two leaf health indicators: the leaf chlorophyll a/b ratio, which was higher in the GNP treatment than in either the control (by 15%) or CB treatment (by 14%), and leaf lipid peroxidation, which was elevated in the CNT treatment compared with either the control (by 47%) or GNP treatment (by 66%). Overall, these results show that, while severe environmental stresses may impair plant production, CNMs (including CNTs and GNPs) in soil could additionally affect foliar health of an agriculturally important legume.

Soybeans Grown with Carbonaceous Nanomaterials Maintain Nitrogen Stoichiometry by Assimilating Soil Nitrogen to Offset Impaired Dinitrogen Fixation

“…Dry powders of MWCNTs and GNPs were purchased from Cheap Tubes Inc. (Grafton, VT, USA), and CB from Dorsett & Jackson Inc. (Printex 30; Los Angeles, CA, USA). All three CNMs have been fully characterized for physicochemical properties that were reported previously. ,, While each varied in their morphologies and sizes, each had at least one dimension under 100 nm. Briefly, MWCNTs had an average outer diameter of 18.8 ± 4.1 nm and a length of 10–30 μm; GNPs were two-dimensional flakes with an average diameter of 350 ± 320 nm and a thickness of 8–12 nm; CB was spherical with a primary particle size of 36.6 ± 8.3 nm. , All CNMs were confirmed to have high purities, as the noncarbon impurities (wt %) were measured to be 2.2%, 1.0%, and 1.3% for MWCNTs, GNPs, and CB, respectively …”

“…The seeds were determined to have an average N concentration of 62 mg g –1 (following the method described below), which fell within the interquartile range of soybean seed N concentrations (60–67.5 mg g –1 ) reported in the literature . Seeds were inoculated with Bradyrhizobium japonicum USDA 110 (U.S. Department of Agriculture, Washington, DC, USA) following a method reported previously. ,, Briefly, seeds were soaked (10 min) in a B. japonicum inoculum (with an optical density at 600 nm of 1.0) before being sown into rehydrated Park’s One-Step Seed Starter peat disks (Park Seed Co., Hodges), followed by an additional 100 μL of the B. japonicum inoculum dispensed onto the planted seed. The disks were placed in trays, watered daily, and incubated on a heating mat (23 °C) for seed germination.…”

“…These concentrations are representative of a wide range of possible environmental exposures ( e . g ., predicted concentrations in biosolids or biosolids-amended soils, potential hotpots, or future soil buildup). ,− To prepare homogenized CNM-amended soils, we used a sequential 10-fold dilution method as described before. , Briefly, CNM dry powders were weighed into soils resulting in doses of 0.01, 10, and 100 g kg –1 dry soil, followed by mixing for ∼10 min using separate hand-held kitchen mixers. These concentrated CNM-soil stocks were then diluted 10-fold twice by adding unamended soil and mechanically mixing similarly to that above, to achieve the final exposure doses of 0.1, 100, and 1000 mg kg –1 dry soil for each type of CNM.…”

“…All three CNMs have been fully characterized for physicochemical properties that were reported previously. 30,56,57 While each varied in their morphologies and sizes, each had at least one dimension under 100 nm. Briefly, MWCNTs had an average outer diameter of 18.8 ± 4.1 nm and a length of 10−30 μm; GNPs were two-dimensional flakes with an average diameter of 350 ± 320 nm and a thickness of 8−12 nm; CB was spherical with a primary particle size of 36.6 ± 8.3 nm.…”

Foreword to the Research Front on ‘Nanotechnology and Agriculture'

“…Biosolids are expected to contain significant quantities of engineered nanomaterials, including carbonaceous nanomaterials such as carbon black, graphenes and fullerenes. Wang et al (2019) found that there were combined effects of exposure to these three types of carbonaceous nanomaterials, biotic and abiotic stressors (insect and heat stress) in soybean. The overall effects of the different stressors, however, were additive in nature and had different endpoints.…”