Peter J. Stoffella’s research while affiliated with University of Florida and other places

With rising food demand, sandy soils are increasingly used in agriculture. Carbon nanomaterials (CNMs) are a potential soil amendment that can enhance soil fertility and health in sandy soils, but most studies have been conducted in controlled greenhouse or laboratory environments. Therefore, there is limited information on the effect of CNMs on soil biochemical properties at the field scale, particularly in comparison with alternative carbon sources (e.g., biochar). We conducted field trials with sugar beet (Beta vulgaris) and field corn (Zea mays) using different application rates of novel water-dispersible CNMs (pH:5.5, zeta-potential: − 40.6 mV, primary particle diameter: 30-60 nm) applied at various rates (100–1200 mg kg⁻¹), and compared CNMs to biochar applied at one rate (1%) along with unfertilized and fertilized controls. We evaluated the comparative effects of CNMs and biochar on soil chemical (pH, EC, N, P, K, C) and biological (respiration, microbial biomass carbon, soil urease, phosphatase and dehydrogenase enzymes) properties at 30DAS (days after sowing), 65/70DAS and after harvest. Biochar significantly raised soil pH while both C amendments reduced soil EC, particularly in soils that weren’t limed. Among fertilized treatments, soil nutrient availability during crop growth was enhanced to a greater extent with CNMs than with biochar, with significant increases in KCl-extractable NO3⁻-N and NH4⁺-N (37–54%), along with P (45–94%; post-harvest samples) and K (18-256%) extractable with Mehlich 3. Soil biological activity with CNMs and the fertilized control was similar at low to medium CNM application rates, but high CNMs doses significantly reduced soil microbial respiration and the activity of urease and dehydrogenase enzymes. Pearson correlations and a principal component analysis highlighted that soil nutrient availability and microbial activity were closely correlated for both crops. Overall, we found that CNMs added at the low-medium application rates (100–400 mg kg⁻¹) was superior to biochar (1%) in improving soil chemical and biochemical properties in sandy soils, providing an additional amendment for the management of marginal lands.

Microplastics and antibiotics are emerging as ubiquitous contaminants in farmland soil, harming crop quality and yield, and thus threatening global food security and human health. However, few studies have examined the individual and joint effects of degradable and/or non-degradable microplastics and antibiotics on crop plants. This study examined the individual and joint effects of polyethylene (PE) and polylactic acid (PLA) microplastics and the antibiotic oxytetracycline (OTC) on pak choi by measuring its growth, photosynthesis, antioxidant enzyme activity, and metabolite levels. Microplastics and/or oxytetracycline adversely affected root weight, photosynthesis, and antioxidant enzyme (superoxide dismutase, catalase, and ascorbate peroxidase) activities. The levels of leaf metabolites were significantly altered, causing physiological changes. Biosynthesis of plant secondary metabolites and amino acids was altered, and plant hormones pathways were disrupted. Separately and together, OTC, PE, and PLA exerted phytotoxic and antagonistic effects on pak choi. Separately and together with OTC, degradable microplastics altered the soil properties, thus causing more severe impacts on plant performance than non-degradable microplastics. This study elucidates the effects on crop plants of toxicity caused by co-exposure to degradable or non-degradable microplastic and antibiotics contamination and suggests mechanisms.

PurposeImproving crop yields by increasing fertilizer-use-efficiency is essential to minimizing agriculture's environmental impact. Water-dispersible carbon nanomaterials (CNM) have emerged as an innovative material to improve crop yields by increasing nutrient utilization and enhancing crop physiological processes. However, the optimum dose of CNM, performance on crop growth, and impact on soil biochemical properties remain poorly understood.MethodsA greenhouse pot experiment (55 days) was conducted to evaluate the effect of three CNM rates, applied basally as a soil drench amendment, on the growth of two lettuce varieties and soil biochemical properties. We compared three CNM rates (200, 400 & 800 mg kg−1; C200F, C400F & C800F) along with a negative control (C0F0; no fertilizer or CNM) and a positive control (C0F; fertilizer at recommended doses like CNM treatments, no CNM applied).ResultsWe found that nitrogen (N), phosphorus and potassium (K) accumulation by lettuce and availability in soil were enhanced with CNM application, with 31% (C200F) and 34% (C400F) increases in shoot N accumulation compared to C0F, and K accumulation peaking at C800F (230% increase over C0F). Compared to C0F, soil microbial biomass carbon was 67–180% (C200F) or 42–150% (CF400) higher, phosphatase enzyme activity was 29–32% higher with C200F, and urease enzyme activity was 37–38% higher at C400F, indicating greater soil biological activity at lower application rates.Conclusion Overall, CNM (200–400 mgkg−1 soil) promoted lettuce growth, enhanced soil fertility and soil biological activity, elucidating that water-dispersible CNM can be an alternative soil amendment to improve crop growth and soil biochemical quality.

Antibiotics and microplastics including nanoplastics are emerging contaminants which have become global environmental issues. The application of antibiotics along with microplastics in soil and their entrance in food chain may pose a major threat to human health. The single and combined exposure of polystyrene microplastic (MPS), norfloxacin (NF) and sulfadiazine (SFD) on Chrysanthemum coronarium L. a medicinal food crop, were investigated. Accumulation of nutrient element contents (Fe, Mn, Mg, Zn, K) differentially responded to the single or combined treatments compared to the control. Scanning electron microscopy and transmission electron microscopy analysis indicated that MPS, NF and SFD accumulated in roots, shoots, and leaves and affected their ultrastructure. Compared with that of the single contamination, the co-contamination of microplastics and antibiotics had a greater effect on leaf metabolites due to combination of multiple abiotic stresses. MPS, NF and SFD accumulated from roots and transported to shoots and leaves which ultimately impacts plant metabolites and, nutritional value. They subsequently impact agricultural sustainability and food safety of medicinal food plants. This investigation suggests the possible ecological risks of microplastics to medicinal food plants, especially in co-exposure with organic pollutants like antibiotics and help to reveal potential mechanisms of phytotoxicity of different antibiotics with polyethylene microplastic.

Introduction of antibiotics into agricultural fields poses serious health risks to humans. This study investigated the uptake of antibiotics, their effects on metabolic pathways, and chloroplast structure changes of Allium tuberosum exposed to norfloxacin (NFL), oxytetracycline (OTC), and tetracycline (TC). Among all the antibiotic treatments, the highest accumulation of antibiotics in roots (4.15 mg/kg) and leaves (0.29 mg/kg) was TC, while in bulbs it was NFL (5.94 mg/kg). OTC was with the lowest accumulation in roots: 0.19 mg/kg, bulbs: 0.18 mg/kg, and leaves: 0.11 mg/kg. The number of mitochondira and the number of plastoglobulli increased. The chloroplast structure was disturbed under the stress of NFL, OTC, and TC. Disturbance in the chloroplast ultrastructure leads to altered chlorophyll fluorescence variables. Simultaneously, metabolomic profiling of leaves demonstrated that NFL stress regulated more of metabolic pathways than OTC and TC. Differences in metabolic pathways among the antibiotic treatments showed that each antibiotic has different impact even under the same experimental conditions. TC and NFL have more toxic effects than OTC antibiotic. Metabolic variations induced by antibiotics stress highlighted pools of metabolites that affect the metabolic activities, chlorophyll fluorescence, ultrastructural adjustments, and stimulate defensive impact in A. tubersoum. These findings provide an insight of metabolic destabilization as well as metabolic changes in defensive mechanism and stress response of A. tuberosum to different antibiotics.

Increasing applications of nanoparticles (NPs) in agriculture have raised potential risks to soil and aquatic ecosystems. A comparative study examining the transport of commonly used NPs in porous media is of critical significance for their application and regulation in agroecosystems. In this study, laboratory column leaching experiments were conducted to investigate the transport and retention of polysuccinimide NPs (PSI-NPs) in two saturated porous media with different grain sizes, as compared with multi-walled carbon nanotubes (MWCNTs), nano-Ag and nano-TiO2. Zeta potential of the NPs was negative at pH6.3 and decreased in an order of PSI-NPs > nano-TiO2 > MWCNTs > nano-Ag. The coarse and fine sands used in this study had negative charges with similar zeta potentials. The movement of NPs was affected by grain size, with larger sizes facilitating mobility while finer sizes favoring retention of NPs in the porous matrix. The retention profile significantly varied between the two sand columns, with more NPs transported to deeper layers in the coarse sand than the fine sand. The relative percentage of NPs detected in leachate was found to be positively correlated with the zeta potential of NPs (r = 0.931). Among the NPs, nano-Ag had the most negative zeta potential, and therefore was the most mobile, followed by MWCNTs and nano-TiO2. Having the least negative zeta potential, PSI-NPs had the lowest mobility, as compared with other NPs regardless of matrix grain size. This work reveals grain size and zeta potential of NPs are major factors that influence transport of NPs along the vertical porous profile, as well as demonstrating the relative unimportance of NP composition, which could serve as important guideline in nanomaterials application, risk assessment, and waste management in agroecosystems.

Antibiotics frequently contaminate agricultural fields and through plant uptake enter into the food chain. This study aimed to explore the effects of antibiotics; tetracycline (TC), oxytetracycline (OTC) and norfloxacin (NF) on the growth, cell ultrastructure, and metabolite pattern of Brassica rapa ssp.chinensis. Oxytetracycline accumulated more than other antibiotics followed by TC and NF. Plant growth, chlorophyll fluorescence, and antioxidant activities were negatively affected under all antibiotic treatments. Ultrastructural investigation of mesophyll of leaves performed by transmission electron microscopy indicated that antibiotic stress caused the changes in thylakoid orientation, number of plastoglobuli, and starch grains. Identification of functional groups through fourier transform infrared analysis indicated that carboxyl group, carbonate and ammonium ions are involved in the adsorption of antibiotics. The metabolic profiling of B.rapa leaves demonstrated that all of the antibiotics treatments distorted phenylalanine, tyrosine and tryptophan biosynthesis, D-glutamine and D-glutamate metabolism, alanine, aspartate and glutamate metabolism, phenylalanine metabolism and TCA cycle. Metabolic alterations as a result of antibiotics stress provide insights of metabolites that affect the physiological changes attributed to antibiotic stress. These results will improve the understanding of antibiotic contamination effects on plants.

Cadmium (Cd) is an inauspicious abiotic traction that not only influences crop productivity and its growth parameters, but also has adverse effects on human health if these crops are consumed. Among crops, leafy vegetables which are the good source of mineral and vitamins accumulate more Cd than other vegetables. It is thus important to study photosynthetic variables, amino acid composition, and ultrastructural localization of Cd differences in response to Cd accumulation between two low and high Cd accumulating Brassica rapa ssp. chinensis L. (pak choi) cultivars, differing in Cd accumulation ability. Elevated Cd concentrations significantly lowered plant growth rate, biomass, leaf gas exchange and concentrations of amino acids collated to respective controls of both cultivars. Electron microscopy indicated that the impact of high Cd level on ultrastructure of leaf cells was associated to affecting cell functionalities, i.e. irregular cell wall, withdrawal of cell membrane, and chloroplast structure which has negative impact on photosynthetic activities, thus causing considerable plant growth suppression. Damage in root cells were observed in the form of enlargement of vacuole. The energy dispersive micro X-ray spectroscopy of both cultivars leaves indicated that cellular structure exhibited exudates of Cd-dense material. Ultrastructural damages and phytotoxicity were more pronounced in high accumulator cultivar as compared to the low accumulator cultivar. These findings are useful in determining the mechanisms of differential Cd-tolerance among cultivars with different Cd tolerance abilities at cellular level.

Interest has been generated in nanotechnology application in agricultural and food systems and understanding ecotoxicity of nanoparticles (NPs) is imperative for ecosystem health and food safety. This study compared the dose-effects of newly synthesized polysuccinimide NPs (PSI-NPs) with multi-walled carbon nanotubes (MWCNTs), nano-Ag and nano-TiO 2 , on soil microbiological and biochemical processes. The effects of NPs varied largely with the type and dose of NPs as well as soil properties. Of the tested NPs, PSI-NPs had no significant perturbance, while the rest of NPs decreased microbial biomass C and N (MBC and MBN), stimulated the microbial metabolic quotient (MMQ), and inhibited dehydrogenase (DA), urease (UA), and phosphatase (PA) activities. Significant dose-effects of MWCNTs, nano-Ag and nano-TiO 2 occurred, and the influences were more intensive at higher application rate (500 ppm). Irrespective of NP type and dose, the effects were severer in Spodosol soil than Alfisol soil. Principle component analysis (PCA) also confirmed that most of the measured indicators were not affected by PSI-NPs, partly affected by MWCNTs, but intensively influenced by nano-Ag and nano-TiO 2. These results highlight the advantages of PSI-NPs over the other NPs for agricultural applications and could facilitate the development of guidelines in regulating NPs application in agroecosystems.

In vitro oral bioaccessibility of Cadmium (Cd) in two low (XGSJ), (SHQI) and two high (CGBC), (SIYM) Cd-accumulating affinity cultivars of Brassica rapa ssp. chinensis L. (pak choi) grown on Cd-contaminated Alfisol soil was assessed. In this study, physiologically based extraction test (PBET) and in vitro gastrointestinal (IVG) were chosen to assess the bioaccessibility for Cd by stimulating human digestion of plant material. The pak choi cultivars were grown on Cd-contaminated soil with six different Cd concentrations (0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mg kg⁻¹). The phytoavailability of Cd in soils was also measured through Mehlich-3 extraction and sequential extraction method. Plants were harvested and analyzed for their total Cd content and afterward extracted using PBET and IVG to provide the estimate of oral bioaccessibility for the human health risks of metal contamination in pak choi.