Arsenic (As) contamination and bioaccumulation are a serious threat to agricultural plants. To address this issue, we checked the efficacy of As tolerant plant growth promoting bacteria (PGPB), zinc oxide nanoparticles (ZnO NPs) and oxalic acid (OA) in Luffa acutangula grown on As rich soil. The selected most As tolerant PGPB i.e Providencia vermicola exhibited plant growth promoting features i.e solubilzation of phosphate, potassium and siderophores production. Innovatively, we observed the synergistic effects of P. vermicola, ZnO NPs (10 ppm) and OA (100 ppm) in L. acutangula grown on As enriched soil (150 ppm). Our treatments both as alone and in combination alleviated As toxicity exhibited by better plant growth and metabolism. Results revealed significantly enhanced photosynthetic pigments, proline, relative water content, total sugars, proteins and indole acetic acid along with As amelioration in L. acutangula. Furthermore, upregulated plant resistance was manifested with marked reduction in the lipid peroxidation and electrolyte leakage and pronounced antagonism of As and zinc content in leaves under toxic conditions. These treatments also improved level of nutrients, abscisic acid and antioxidants to mitigate As toxicity. This marked improvement in plants’ defense mechanism of treated plants under As stress is confirmed by less damaged leaves cell structures observed through the scanning electron micrographs. We also found substantial decrease in the As bioaccumulation in the L. acutangula shoots and roots by 40 and 58% respectively under the co-application of P. vermicola, ZnO NPs and OA in comparison with control. Moreover, the better activity of soil phosphatase and invertase was assessed under the effect of our application. These results cast a new light on the application of P. vermicola, ZnO NPs and OA in both separate and combined form as a feasible and ecofriendly tool to alleviate As stress in L. acutangula.

Red mud was a highly alkaline hazardous waste, and their resource utilization was a research hotspot. In this study, influencing mechanisms of red mud based passivator on the transformation of Cd fraction in acidic Cd-polluted soil, photosynthetic property, and Cd accumulation in edible amaranth were investigated based on the evaluation of Cd adsorption capacity, root metabolic response, and soil aggregate distribution. Results showed that red mud exhibited good Cd adsorption capacities at about 35 °C and pH 9 in an aqueous solution, and the adsorption behavior of red mud on Cd in rhizosphere soil solution was considered to have some similarity. In the soil-pot trial, red mud application significantly facilitated edible amaranth growth by enhancing the maximum photochemical efficiency and light energy absorption by per unit leaf area by activating more reaction centers. The main mechanisms of rhizosphere soil Cd immobilisation by red mud application included: i) the reduction of mobilized Cd caused by the increasing negative surface charge of soil and precipitation of Cd hydroxides and carbonates at high pH; ii) the increase of organics-Cd complexes caused by the increasing –OH and –COOH amounts adsorbed on the surface of rhizosphere soil after red mud application; and iii) the decrease of available Cd content in soil aggregates caused by the increasing organic matters after red mud application. This study would provide the basis for the safe utilization of red mud remediating acidic Cd-polluted soil.

Currently, there is a lack of information about the influence of foliar-applied nanoplastics on crop growth and nutritional quality. To fill the knowledge gap, soil-grown lettuces (Lactuca sativa L.) were foliar-exposed to polystyrene nanoplastics (PSNPs) at 0, 0.1 and 1 mg/L for one month. Foliar exposure to PSNPs significantly decreased the dry weight, height, and leaf area of lettuce by 14.3%–27.3%, 24.2%–27.3%, and 12.7%–19.2%, respectively, compared with the control. Similarly, plant pigment content (chlorophyll a, b and carotenoid) was considerably reduced (9.1%, 8.7%, 12.5%) at 1 mg/L PSNPs. However, the significant increase in electrolyte leakage rate (18.6%–25.5%) and the decrease in total antioxidant capacity (12.4%–26%) were the key indicators of oxidative stress in lettuce leaves, demonstrating the phytotoxicity of PSNPs by foliar exposure. In addition, the remarkable reduction in micronutrients and essential amino acids demonstrated a decrease in nutritional quality of lettuce caused by PSNPs. Besides, SEM and TEM analysis indicated the possible absorption of PSNPs through leaves stoma and the translocation downwards to plant roots. This study provides new information about the interaction of airborne NPs with plants. It also warns against atmospheric NPs pollution that the adverse effects of airborne NPs on crop production and food quality should be assessed as a matter of urgency.

Plastic residues have become a serious environmental problem in areas where agricultural plastic film are used intensively. Although numerous of studies have been done to assess its impacts on soil quality and crop yields, the understanding of meso-plastic particles effects on plant is still limited. In this study, low density polyethylene (PE) and biodegradable plastic (Bio) mulch film were selected to study the effects of meso-plastic debris on soybean germination and plant growth with the accumulation levels of 0%, 0.1%, 0.5% and 1% in soil (w: w, size ranging 0.5–2 cm) by a pot experiment under field condition. Results showed that the germination viability of soybean seeds was reduced to 82.39%, 39.44% and 26.06% in the treatments with 0.1%, 0.5% and 1% added plastic debris compared to the control (CK), respectively, suggesting that plastic residues in soil inhibit the viability of soybean seed germination. The plastic debris had a significant negative effect on plant height and culm diameter during the entire growth stage of soybean. Similarly, the leaf area at harvest was reduced by 1.97%, 6.86% and 11.53% compared to the CK in the treatments with 0.1%, 0.5% and 1% plastic debris addition, respectively. In addition, the total plant biomass under plastic addition was reduced in both the flowering and harvesting stages, compared to the CK. For the different type of plastic residues, plant height, leaf area and root/shoot ratio at group PE were significantly lower than those of groups treated by Bio. In conclusion, PE debris had a greater negative effects on plant height, culm diameter, leaf area and root/shoot ratio while Bio debris mainly showed the adverse effects on germination viability and root biomass especially at the flowering stage. Therefore, further research is required to elaborate plastic particles’ effects on different stages of crops and soil quality.

Plants can intercept airborne particulate matter through deposition. Different types of plants exhibit different functional leaf traits, which can affect the dry deposition velocity (Vd). However, the most crucial leaf traits of coniferous and broadleaved trees remain unidentified. In this study, we selected 18 typical plants from the subtropical monsoon regions, where PM₂.₅ (fine particulate matter with a diameter of ≤2.5 μm) concentrations are relatively high, and classified them into coniferous and broadleaved categories. Subsequently, we analyzed the relationships between Vd and leaf surface free energy (SFE), single leaf area (LAₛ), surface roughness (SR), specific leaf area (SLA), epicuticular wax content (EWC), and width-to-length ratio (W/L). The results indicated that most coniferous trees exhibited a high Vd. The correlation analysis revealed that SFE, SR, LAₛ, and W/L were the key factors that affected the Vd of all the tested species. SFE and SLA had the strongest influence on the Vd of broadleaved trees, whereas LAₛ and SLA had the strongest effect on that of coniferous trees. Most coniferous trees had a high SLA, which can reduce water loss and hinder particle deposition. However, the stiff leaves of coniferous trees fluttered less, resulting in a larger leaf area that enhanced the capture efficiency. The leaf structure of broadleaved trees is more flexible, resulting in erratic flutter, which may impede deposition and lead to high resuspension. Coniferous and broadleaved trees may have different dominant leaf traits that affect particle deposition.

Population growth, urbanization, environmental conditions and rapid development have caused particulate matter (PM) levels to rise above all national and international health standards during the last two decades in many South-East Asian countries. These PM levels needs to be reduced urgently as they increase the risk of cardiovascular and respiratory health problems for millions of people. Plants have shown to efficiently reduce PM in the air by accumulation on their leaves. In order to investigate which plant species accumulate most PM, we screened 49 common plant species for their PM accumulation capacity in one of the tropical cities with the highest PM concentrations of the world, Hanoi (Vietnam). Using this subset of plants, we tested if certain leaf characteristics (leaf hydrophilicity, stomatal densities and the specific leaf area) can predict the PM accumulation efficiency of plant species. Our results show that the PM accumulation capacity varies substantially among species and that Muntingia calabura accumulated most PM in our subset of plants. We observed that plants with hydrophilic leaves, a low specific leaf area and a high abaxial stomatal density accumulated significantly more PM. Plants with these characteristics should be preferred by urban architects to reduce PM levels in tropical environments.

Influences of ozone (O3) on light-saturated rates of photosynthesis in crop leaves have been well documented. To increase our understanding of O3 effects on individual- or stand level productivity, a mechanistic understanding of factors determining canopy photosynthesis is necessary. We used a canopy model to scale photosynthesis from leaf to canopy, and analyzed the importance of canopy structural and leaf ecophysiological characteristics in determining canopy photosynthesis in soybean stands exposed to 9 concentrations of [O3] (37–116 ppb; 9-h mean). Light intensity and N content peaked in upper canopy layers, and sharply decreased through the lower canopy. Plant leaf area decreased with increasing [O3] allowing for greater light intensity to reach lower canopy levels. At the leaf level, light-saturated photosynthesis decreased and dark respiration increased with increasing [O3]. These data were used to calculate daily net canopy photosynthesis (Pc). Pc decreased with increasing [O3] with an average decrease of 10% for an increase in [O3] of 10 ppb, and which was similar to changes in above-ground dry mass production of the stands. Absolute daily net photosynthesis of lower layers was very low and thus the decrease in photosynthesis in the lower canopy caused by elevated [O3] had only minor significance for total canopy photosynthesis. Sensitivity analyses revealed that the decrease in Pc was associated with changes in leaf ecophysiology but not with decrease in leaf area. The soybean stands were very crowded, the leaves were highly mutually shaded, and sufficient light for positive carbon balance did not penetrate to lower canopy leaves, even under elevated [O3].

Emission of BVOC (Biogenic Volatile Organic Compounds) from plant leaves in response to ozone exposure (O3) and nitrogen (N) fertilization is poorly understood. For the first time, BVOC emissions were explored in a forest tree species (silver birch, Betula pendula) exposed for two years to realistic levels of O3 (35, 48 and 69 ppb as daylight average) and N (10, 30 and 70 kg ha−1 yr−1, applied weekly to the soil as ammonium nitrate). The main BVOCs emitted were: α-pinene, β-pinene, limonene, ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and hexanal. Ozone exposure increased BVOC emission and reduced total leaf area. The effect on emission was stronger when a short-term O3 metric (concentrations at the time of sampling) rather than a long-term one (AOT40) was used. The effect of O3 on total leaf area was not able to compensate for the stimulation of emission, so that responses to O3 at leaf and whole-plant level were similar. Nitrogen fertilization increased total leaf area, decreased α-pinene and β-pinene emission, and increased ocimene, hexanal and DMNT emission. The increase of leaf area changed the significance of the emission response to N fertilization for most compounds. Nitrogen fertilization mitigated the effects of O3 exposure on total leaf area, while the combined effects of O3 exposure and N fertilization on BVOC emission were additive and not synergistic. In conclusion, O3 exposure and N fertilization have the potential to affect global BVOC via direct effects on plant emission rates and changes in leaf area.

Tree canopies play a key role in the cycling of polycyclic aromatic hydrocarbons (PAHs) in terrestrial ecosystems, as leaves can capture PAHs from the air. In this study, accumulation of PAHs was compared in an evergreen species, P. pinaster, and in a deciduous species, Q. robur, in relation to some physio-morphological characteristics. For this purpose, pine needles and oak leaves collected from different sites across Galicia (NW Spain) were analysed to determine PAH contents, specific leaf area, stomatal density and conductance.Leaves and needles contained similar total amounts of PAHs. The major contribution of particle-bound PAHs in oak (the concentrations of 4- and 5-ring PAHs were two times higher, and those of 6-ring PAHs five times higher in oak than in pine) may be related to the higher specific leaf area (13 and 4 cm2 g−1 dry mass in respectively oak and pine). However, the major contribution of vapor-phase PAHs in pines may be affected by the stomatal conductance (two times higher in pine than in oak). Moreover, an increase in the diameter at breast height of trees led to an increase in accumulation of PAHs, with pine capturing higher amounts of low and medium molecular weight PAHs. The study findings underline the potential role of trees in improving air quality, taking into account the canopy biomass and life cycle.

Biomagnetic monitoring of urban tree leaves has proven to be a good estimator of ambient particulate matter. We evaluated its relevancy by determining leaf area normalised weight (mg m−2) and SIRM (A) of leaf-deposited particles within three different size fractions (>10 μm, 3–10 μm and 0.2–3 μm) and the SIRM of the leaf-encapsulated particles. Results showed that throughout the in-leaf season, the trees accumulated on average 747 mg m−2 of dust on their leaves, of which 74 mg m−2 was within the 0.2–10 μm (∼PM10) size range and 40 mg m−2 within the 0.2–3 μm (∼PM3) size range. A significant correlation between the SIRM and weight of the surface-deposited particles confirms the potential of biomagnetic monitoring as a proxy for the amount of leaf-deposited particles. Spatial variation of both SIRM and weight throughout the street canyon suggests traffic and wind as key factors for respectively the source and distribution of urban particulates.