Frequent drought events and particulate matter pollution from vehicular exhaust seriously affect urban plant growth and provisioning of ecological services. Yet, how plants respond physiologically and morphologically to these two combined stressors remains unknown. Here, we assessed particle retention dynamics and plant morphology and physiology of Euonymus japonicus Thunb. var. aurea-marginatus Hort. under continuous drought with severe exhaust exposure. Our results showed that continuous drought insignificantly lowered particle retention in each of three size fractions by 1.02 μg·cm⁻² on average in the first 28 days, but significantly lowered total particle retention by 35.75 μg·cm⁻² on the 35th day. We observed evident changes in morphology, leaf mass per area (LMA), pigments, gas exchange in all stressed plants. Compared with single stress, combined drought and pollution caused earlier yellowing and shedding of old leaves, significantly lowered LMA by 1.21 mg·cm⁻², caused a greater decline in pigments and net photosynthetic rate (Pₙ). Large particles may mainly explain pigment reduction, lower weekly LMA increases, and stomatal restriction, while coarse particles may be the main drivers of the decline in Pₙ. Continuous drought mediated the influence of all three particle sizes on some parameters, such as weakening the impact of total particles on LMA, strengthening the impact of fine particles on photosynthesis. Our findings suggest that drought accelerates the physiological responses of plants to exhaust pollution. Under controlled severe exhaust pollution conditions, the optimal time to maintain high particle retention during continuous drought without decline in physiological conditions for E. japonicus var. aurea-marginatus was 14 days. Some additional interventions after 14 days (it could be postponed appropriately under field conditions) may help ensure healthy growth of plants and retention of particulate matter.

Artificial light at night (ALAN) is a recognised disruptor of biological function and ecological communities. Despite increasing research effort, we know little regarding the effect of ALAN on woody plants, including trees, or its indirect effects on their colonising invertebrates. These effects have the potential to disrupt woodland food webs by decreasing the productivity of invertebrates and their secretions, including honeydew and lerps, with cascading effects on other fauna. Here, we cultivated juvenile river red gums (Eucalyptus camaldulensis) for 40 weeks under experimentally manipulated light (ALAN) or naturally dark (control) conditions. To assess direct impacts on tree growth, we took multiple measures of growth at four time periods, and also measured physiological function, biomass and investment in semi-mature trees. To assess experimentally the direct and indirect (tree-mediated) impacts of ALAN on invertebrates, from 19 weeks onwards, we matched and mismatched trees with their original ALAN environments. We colonised trees with a common herbivore of E. camaldulensis, the red gum lerp psyllid (Glycaspis nr. brimblecombei) and then measured the effects of current and historic tree lighting treatment on the psyllid life cycle. Our data revealed direct effects of ALAN on tree morphology: E. camaldulensis trees exposed to ALAN shifted biomass allocation away from roots and into leaves and increased specific leaf area. However, while the intensity of ALAN was sufficient to promote photosynthesis (net carbon gain) at night, this did not translate into variation in tree water status or photosystem adaptation to dim night-time light for ALAN-exposed trees. We found some evidence that ALAN had broad-scale community effects—psyllid nymphs colonising ALAN trees produced more lerps—but we found no other direct or indirect impacts of ALAN on the psyllid life cycle. Our results suggest that trees exposed to ALAN may share morphological responses with trees under dim daylight conditions. Further, ALAN may have significant ‘bottom-up’ effects on Eucalyptus woodland food webs through both trees and herbivores, which may impact higher trophic levels including woodland birds, mammals and invertebrates.

Microplastic pollution is a recognized hazard in aquatic systems, but in the past decade has emerged as a pollutant of interest in terrestrial ecosystems. This paper is the first formal meta-analysis to examine the phytotoxic effects of microplastics and their impact on soil functions in the plant-soil system. Our specific aims were to: 1) determine how the type and size of microplastics affect plant and soil health, 2) identify which agricultural plants are more sensitive to microplastics, and 3) investigate how the frequency and amount of microplastic pollution affect soil functions. Plant morphology, antioxidant production and photosynthesis capacity were impacted by the composition of polymers in microplastics, and the responses could be negative, positive or neutral depending on the polymer type. Phytotoxicity testing revealed that maize (Zea mays) was more sensitive than rice (Oryza sativa) and wheat (Triticum aestivum) within the Poaceae family, while wheat and lettuce (Lactuca sativa) were less sensitive to microplastics exposure. Microplastics-impacted soils tend to be more porous and retain more water, but this did not improve soil stability or increase soil microbial diversity, suggesting that microplastics occupied physical space but were not integrated into the soil biophysical matrix. The meta-data revealed that microplastics enhanced soil evapotranspiration, organic carbon, soil porosity, CO₂ flux, water saturation, nitrogen content and soil microbial biomass, but decreased soil N₂O flux, water stable aggregates, water use efficiency, soil bulk density and soil microbial diversity.

In the present study, endpoints including in vitro pollen performance (i.e., germination and tube growth) and lethality were used as assessments of nanotoxicity. Pollen was treated with 5–10 nm-sized Pd particles, similar to those released into the environment by catalytic car exhaust converters. Results showed Pd-nanoparticles altered kiwifruit pollen morphology and entered the grains more rapidly and to a greater extent than soluble Pd(II). At particulate Pd concentrations well below those of soluble Pd(II), pollen grains experienced rapid losses in endogenous calcium and pollen plasma membrane damage was induced. This resulted in severe inhibition and subsequent cessation of pollen tube emergence and elongation at particulate Pd concentrations as low as 0.4 mg L−1. Particulate Pd emissions related to automobile traffic have been increasing and are accumulating in the environment. This could seriously jeopardize in vivo pollen function, with impacts at an ecosystem level. Nanoparticulate Pd – which resembles emissions from automobile catalysts – affects pollen to a higher extent than soluble Pd.

Iron is recognized as an efficient method to alleviate sulfide stress. This study tested the response of Zostera marina plants to different levels of sedimentary sulfides (100.0–818.7 μmol L⁻¹) and iron inputs (590.0–825.3 μg L⁻¹) in a field experiment performed over an eighty-day period. We measured plant responses in terms of shoot density and plant morphology and productivity. The relationship between the propagation effort (PE, in %) and sulfide content (S, in μmol L⁻¹) was expressed as: PE = −14.01 × ln (S) + 86.86 (R² = 0.99, p < .01), which indicates that the toxic limit of the pore-water sulfide concentration for the survival of eelgrass is 493 μmol L⁻¹. The addition of iron can reduce the toxicity of sulfides to eelgrass beds, resulting in an increase in plant density and productivity, and can even reverse the decline of eelgrass beds exposed to high sulfide concentrations.

In situ revegetation is effective in improving water-stable aggregation, preserving structural stability, and decreasing groundwater pollution to reduce the environmental risks posed by alkaline bauxite residue (ABR). Pseudomonas simiae, a plant growth-promoting rhizobacteria (PGPR), was used to promote Atriplex canescens growth challenged by ABR. The mechanism of P. simiae-induced plant growth promotion and tolerance against ABR stresses has been investigated. P. simiae was shown to alleviate ABR-induced stress in A. canescens by regulating photosynthesis and transpiration, inducing antioxidant defense, causing osmolyte accumulation, and altering plant morphology. Shoot dry weight, root dry weight, and root length of A. canescens were increased by 5.9%, 6.7%, and 11.5%, respectively, after inoculation with P. simiae for 60 days. Thus, it seems that P. simiae systemically regulated physiological processes in A. canescens favoring its growth under ABR treatments.

The influence of cadmium on growth, cadmium accumulation, composition, and content of glucosinolates was investigated in Arabidopsis thaliana after 4 weeks of growth in hydroponics. Accumulation of 3,820 and 321 μg Cd g⁻¹ dry weight in the roots and leaves of A. thaliana, respectively, exposed to 50 μM Cd. Cadmium treatment significantly decreased the total concentration of glucosinolates both in the leaves and roots. Cd-induced alteration of total glucosinolate content in the roots was mainly due to the decrease of indolyl-glucosinolates. In the Cd treatment leaves, significant decreases were, respectively, detected for glucoibervirin and 4-methoxyglucobrassicin (P < 0.01), while other glucosinolate levels did not decrease significantly. In response to cadmium, the three indolyl-glucosinolates all showed significant decreases in the roots. The distinctive influence of cadmium on glucosinolate profiles in Cd-sensitive A. thaliana may be of great ecological importance, decreasing the resistance to phytophage attack. Taken together, our data is discussed in relation to jasmonic acid and salicylic acid as possible molecules that modulate the alteration of glucosinolate profiles in response to cadmium. The similar effects of Cd treatment on the levels of individual glucosinolates in leaves and roots were observed at higher-concentration cadmium treatment (100 μM Cd).

The aim of this study was to characterize qualitatively and quantitatively the composition of the main rhizodeposits emitted from maize (Zea mays) under Cd stress, in order to discuss their role in Cd availability and tolerance. Maize was grown for 6 weeks in sand at four Cd exposure levels (0, 10, 20, and 40 μM Cd in nutrient solution) and two types of rhizodeposits were collected at the end of cultivation period. Mucilage and other molecules adhering to rhizospheric sand were extracted with a buffer before root exudates were collected by diffusion into water. Total carbon, proteins, amino acids, and sugars were analyzed for both rhizodeposit types and about 40 molecules were identified using GC-MS and LC-MS. Cadmium effect on plant morphology and functioning was slight, but consistent with previous works on Cd toxicity. However, rhizodeposition did tend to be impacted, with a decrease in total carbon, sugars, and amino acids correlating with an increasing Cd content. Such a decrease was not noticeable for proteins in root exudates. These observations were confirmed by the same trends in individual compound contents, although the results were generally not statistically significant. Many of the molecules determined are well-known to modify, whether directly or indirectly, Cd speciation and dynamics in the soil and could play a role in Cd tolerance.

Anthropogenic activities are a major source for contaminating the agricultural soil with heavy metals, which can affect physiological and metabolic processes in plants. Among the heavy metals, chromium (Cr) is the most toxic pollutant that negatively affects plants’ metabolic activities, growth, and yield. Chromium reduces the plant growth and development by influencing the photosynthetic performance and antioxidant enzyme activities. This study was designed to examine the promotive role of exogenously applied glycinebetaine (GB) on plant morphophysiological and biochemical attributes in cauliflower (Brassica oleracea botrytis L.) under Cr toxicity. Four levels (0, 10, 100, and 200 μM) of Cr were tested under the application of GB (1 mM). The results delineated that Cr stress caused a considerable reduction in plant growth, photosynthetic pigment, gas exchange parameters, and biomass production. At high concentration (200 μM), chromium stress decreased the plant height (57%), root length (32%), number of leaves (45%), and leaf area (29%) as compared with controls. Due to Cr stress, the electrolyte leakage and accumulation of malondialdehyde and hydrogen peroxide increased both in the roots and leaves of cauliflower, whereas antioxidative enzyme activities (SOD, CAT, and POD) decreased both in the roots and leaves of cauliflower due to Cr stress. At 200 μM of chromium treatment, root dry weight, stem dry weight, leaf dry weight, and flower dry weight declined up to 43%, 40%, 53%, and 72%, respectively. With the application of GB, dry biomass of plant increased significantly as compared with no GB treatment under chromium stress. As Cr level increased in growth media, its concentration also increased in all plant parts including roots, stem, leaves, and flowers. However, GB application efficiently alleviated the Cr toxic effects on cauliflower and maintained higher plant growth, biomass production, photosynthetic attributes, and gas exchange traits as compared with their respective controls. Exogenously applied GB decreased oxidative stress and improved antioxidative enzyme activities as compared with treatments without GB application. Furthermore, Cr concentrations taken by plants were decreased due to GB application. These findings suggest that GB can play a positive role to maintain plant morphology and photosynthetic attributes under Cr toxic conditions in cauliflower.