Local plant responses to global problems: Dactylis glomerata responses to different traffic pollutants on roadsides

Biomonitoring and phytoremediation potential of Conocarpus erectus (Buttonwood) for mitigating air pollution from highway traffic

This study investigates the impact of vehicular-released heavy metals (Zn, Fe, Pb, Cd, and Ni) on foliar physiological and biochemical parameters of Conocarpus erectus and its relationship with the Air Pollution Tolerance Index (APTI). Leaf samples were collected from six sites along a busy road (Bahawalpur to Rahim Yar Khan, KLP Road) in Punjab, Pakistan, during the spring season, with control samples taken 50 m away from the roadside. Heavy metal concentrations were analyzed using an Atomic Absorption Spectrophotometer (AAS), revealing significantly higher levels of Pb, Cd, Ni, and Cu in leaf dust at polluted sites, particularly in Ahmadpur. Exposure to heavy metal pollution led to notable reductions in shoot length, leaf area, and biomass, with Khanbella exhibiting the most severe declines. Gas exchange parameters were altered, with increased CO2 assimilation and stomatal conductance at Taranda, while transpiration rates decreased across polluted sites. Biochemical responses, including elevated total soluble proteins, free amino acids, and ascorbic acid, indicated adaptive metabolic shifts. Photosynthetic pigments, particularly chlorophyll b and carotenoids, were significantly reduced under pollution stress, whereas antioxidant activity remained stable. Anatomical modifications, such as increased vascular bundle and cortical thickness at Taranda and Iqbalabad, reflected structural resilience. Stomatal density and area were significantly lower at polluted sites, suggesting regulatory adjustments to minimize water loss. APTI values (12.21-9.98) were significantly higher at roadside locations compared to controls, highlighting the strong resilience of C. erectus to pollution. The species high APTI values and capacity to tolerate heavy metal contamination suggest its suitability for urban roadside plantations, where it can mitigate the adverse effects of vehicular emissions and contribute to environmental sustainability.

Micro-morphological response of some native dicotyledonous species to particulate pollutants emitted from stone crushing activities

Stone crushing processes release particulates and associated noxious substances in our surroundings that are continuously destructing environmental conditions and ecosystem health. Morpho-anatomical changes in some medicinally important native species (Aerva javanica, Calotropis procera, Digera muricata, Euphorbia prostrata, Euploca strigosa, and Peganum harmala) exposed to heavy dust pollution were evaluated. These species selected on the basis of their ubiquitous distribution in the area. Two sites were selected in the Kirana Hills, Sargodha, one near stone crushers within 500-m radius (polluted) and the other 4 km away from the crushers (control) varying significantly in amount of dust particles received. A decrease in plant height of all species from dust-polluted sites was observed. Reduction in height was more prominent in species like C. procera and D. muricata. Stem sclerification increased in C. procera and E. prostrata from the polluted site that is an indication of better tolerance to dust pollution. C. procera showed increased stem and leaf epidermis, stem sclerenchyma, and stem vascular bundles, which can increase resistance to dust pollution. E. strigosa was the most sensitive species in which all morpho-anatomical factors decreased. Survival of plant species depended on specific structural modifications in dermal, mechanical, parenchymatous, and vascular tissue. Overall, dust pollution severely affected plant morphological and micro-morphological traits, but the response of selected species to dust pollution was variable. It is concluded that stem and leaf anatomical traits like size of dermal and storage tissue thickness and stomatal density are good indicators for biomonitoring of dust pollution.

Heavy metal concentrations in roadside plants (Achillea wilhelmsii and Cardaria draba) and soils along some highways in Hamedan, west of Iran

The present study was conducted to analyze the effects of traffic volumes on Cd, Cu, Pb, Ni, and Zn contents in roadside soils and in two dominant herbaceous species (Achillea wilhelmsii and Cardaria draba) along highways and to evaluate the dynamic characteristics of these elements and their accumulation by the aerial parts and roots of these herbaceous species. The plant samples were collected along 700 m of a 9-km segment of each of the three major highways in Hamedan Province (West Iran) with different traffic volumes: Hamedan-Goltapeh (HG), Hamedan-Razan (HR), and Hamedan-Kermanshah (HK). The results indicated that the mean contents of Cd, Cu, Pb, Ni, and Zn in the soil samples were 0.26, 18.74, 14.98, 18.21, and 62.25 mg kg^-1, respectively. Furthermore, the mean contents of elements (mg kg^-1) in aerial parts of A. wilhelmsii were 0.16 for Cd, 4.52 for Cu, 1.91 for Pb, 1.70 for Ni, and 44.80 for Zn, while in the aerial part samples of C. draba, the concentrations (mg kg^-1) and the mean contents were 0.16, 2.29, 2.58, 1.60, and 31.29, respectively. This meant that the traffic volume affected the contents of the metals in the soil and the herbaceous species. The metal content in herbaceous tissues varied significantly between plant species. A. wilhelmsii tended to accumulate the metals in the roots while C. draba retained them mostly in the aerial parts. The significant positive correlations of Cd, Cu, Ni, and Zn content in root and aerial parts of the herbaceous plant with those found in the soil samples showed the potential of the studied species for application in biomonitoring studies. Comprehensive analysis (effect of traffic volumes and relationships between the content of elements in plant tissues and soil samples) indicated that Cu in both herbaceous plants was mainly derived from soil, while A. wilhelmsii absorbed Cd and C. draba absorbed Zn mainly through the stomata from atmospheric depositions. Without considering atmospheric depositions due to intense traffic volumes, in A. wilhelmsii, the translocation factor (TF) values of Cu and Zn were 1.06 and 1.44, respectively and in C. draba, the TF values of Cd, Cu, and Pb were 1.06, 1.09, and 1.13, respectively, thus suggesting that both herbaceous species had high potentials for transferring metals from the roots to aerial parts.

Herbicide effectiveness in controlling invasive plants under elevated CO2: Sufficient evidence to rethink weeds management

Previous studies have reported that chemical weed control will be less effective for some weed species under future atmospheric CO₂ concentrations. Such reductions in plant sensitivity to herbicides under elevated CO₂ may be due to greater biomass accumulation and differences among growth types. However, these studies have been limited to few growth types (herbaceous and grass species) and to a single herbicide (glyphosate). This study tested a more extensive range of weed species (both in number and growth form) and herbicides to assess general patterns of plant response. We grew 14 environmental weed species representing four different growth forms (grasses, herbs, shrubs and vines), that are commonly found in south-eastern Australia, under ambient (380 ppm) and elevated (550 ppm) CO₂ concentrations. We then applied the recommended and double-recommended concentrations of two herbicides: glyphosate and fluroxypyr-meptyl. We found that responses of the weed species to herbicide under elevated CO₂ were species-specific. However, the C₃ grasses tended to be the most sensitive to herbicide application followed by the herbs and C₄ grasses while shrubs and vines demonstrated the highest resistance. Our results highlight the need for broader testing to determine the species most likely to exhibit increased tolerance to herbicide in the future in order to improve management options beforehand and thus offset a future liability.