Atmospheric pollution could significantly alter tree growth independently and synergistically with meteorological conditions. North China offers a natural experiment for studying how plant growth responds to air pollution under different meteorological conditions, where rapid economic growth has led to severe air pollution and climate changes increase drought stress. Using a single aspen clone (Populus euramericana Neva.) as a ‘phytometer’, we conducted three experiments to monitor aspen leaf photosynthesis and stem growth during in situ exposure to atmospheric pollutants along the urban-rural gradient around Beijing. We used stepwise model selection to select the best multiple linear model, and we used binned regression to estimate the effects of air pollutants, atmospheric moisture stress and their interactions on aspen leaf photosynthesis and growth. Our results indicated that ozone (O₃) and vapor pressure deficit (VPD) inhibited leaf photosynthesis and stem growth. The interactive effect of O₃ and VPD resulted in a synergistic response: as the concentration of O₃ increased, the negative impact of VPD on leaf photosynthesis and stem growth became more severe. We also found that nitrogen (N) deposition had a positive effect on stem growth, which may have been caused by an increase in canopy N uptake, although this hypothesis needs to be confirmed by further studies. The positive impact of aerosol loading may be due to diffuse radiation fertilization effects. Given the decline in aerosols and N deposition amidst increases in O₃ concentration and drought risk, the negative effects of atmospheric pollution on tree growth may be aggravated in North China. In addition, the interaction between O₃ and VPD may lead to a further reduction in ecosystem productivity.

The experiment was carried out on a short rotation coppice culture of poplars (POP-EUROFACE, Central Italy), growing in a free air carbon dioxide enriched atmosphere (FACE). The specific objective of this work was to study whether elevated CO2 and fertilization (two CO2 treatments, elevated CO2 and control, two N fertilization treatments, fertilized and unfertilized), as well as the interaction between treatments caused an unbalanced nutritional status of leaves in three poplar species (P. x euramericana, P. nigra and P. alba). Finally, we discuss the ecological implications of a possible change in foliar nutrients concentration. CO2 enrichment reduced foliar nitrogen and increased the concentration of magnesium; whereas nitrogen fertilization had opposite effects on leaf nitrogen and magnesium concentrations. Moreover, the interaction between elevated CO2 and N fertilization amplified some element unbalances such as the K/N-ratio. CO2 enrichment reduced foliar nitrogen and increased the magnesium concentration in poplar.

We investigated isoprene (ISO) emission and gas exchange in leaves from different positions along the vertical canopy profile of poplar saplings (Populus euramericana cv. ‘74/76’). For a growing season, plants were subjected to four N treatments, control (NC, no N addition), low N (LN, 50 kg N ha⁻¹year⁻¹), middle N (MN, 100 kg N ha⁻¹year⁻¹), high N (HN, 200 kg N ha⁻¹year⁻¹) and three O₃ treatments (CF, charcoal-filtered ambient air; NF, non-filtered ambient air; NF + O₃, NF + 40 ppb O₃). Our results showed the effects of O₃ and/or N on standardized ISO rate (ISOᵣₐₜₑ) and photosynthetic parameters differed along with the leaf position, with larger negative effects of O₃ and positive effects of N on ISOᵣₐₜₑ and photosynthetic parameters in the older leaves. Expanded young leaves were insensitive to both treatments even at very high O₃ concentration (67 ppb as 10-h average) and HN treatment. Significant O₃ × N interactions were only found in middle and lower leaves, where ISOᵣₐₜₑ declined by O₃ just when N was limited (NC and LN). With increasing light-saturated photosynthesis and chlorophyll content, ISOᵣₐₜₑ was reduced in the upper leaves but on the contrary increased in middle and lower leaves. The responses of ISOᵣₐₜₑ to AOT40 (accumulated exposure to hourly O₃ concentrations > 40 ppb) and PODY (accumulative stomatal uptake of O₃ > Y nmol O₃ m⁻² PLA s⁻¹) were not significant in upper leaves, but ISOᵣₐₜₑ significantly decreased with increasing AOT40 or PODY under limited N supply in middle leaves but at all N levels in lower leaves. Overall, ISOᵣₐₜₑ changed along the vertical canopy profile in response to combined O₃ and N exposure, a behavior that should be incorporated into multi-layer canopy models. Our results are relevant for modelling regional isoprene emissions under current and future O₃ pollution and N deposition scenarios.

International audience | Polycyclic aromatic hydrocarbon (PAH) contamination in industrial soils poses significant environmental challenges, necessitating cost-effective bioremediation approaches like tree-based phytoremediation. However, the defence mechanisms and adaptability of trees to PAH exposure remain poorly understood, while the identification of molecular markers could help in the detection of toxicity symptoms. This study explores the molecular response of Populus canadensis to a phenanthrene (PHE) contamination gradient (from 100 to 2000 mg kg−1) using RNA-seq analysis of roots and leaves after 4 weeks of exposure. Both differentially expressed genes (DEGs) and DRomics, a dose–response tool, identified transcriptomic changes, with about 50% of deregulated genes responding significantly at a benchmark dose (i.e. minimal dose that produces a significant effect) below 400 mg PHE kg−1. The highest number of DEGs was found both at a low concentration (200 and 700 mg kg−1) and at the highest concentrations (1500–2000 mg kg−1) for both roots and leaves. Ethylene signalling genes were activated via ABA-independent pathways at low concentrations and ABA-dependent pathways at high concentrations. Across the gradient, responses to oxidative stress were triggered, including reactive oxygen species scavenging and phenylpropanoid biosynthesis, specifically at 1500–2000 mg kg−1. Additionally, PHE disrupted pathways related to plant responses to biotic stress. These findings revealed unexpected dose-dependent transcriptomic shifts, demonstrating poplar’s adaptive defence mechanisms against PHE toxicity.

Stem cuttings with homogenous diameter of Populus x euramericana (clone I-214) and Salix fragilis L. were grown in growth chamber in water culture method. After 45 days, the plants were treated with 10−7 and 10−5 M cadmium (Cd). As these species have different phytoextraction potentials, there is a need to analyze the level of Cd uptake, its translocation into aboveground organs, and changes in leaf structure. We analyzed micromorphological leaf characteristics: a fresh mass of the root, stem, and leaf, as well as a Cd concentration within them. Besides, we compared 23 micromorphological leaf blade quantitative traits of poplar and willow and monitored the structural changes induced by the intoxication of stem cuttings. Percent of Cd accumulation and translocation in plant organs varied between species. It depended on the level of Cd applied. When compared to the poplar clone, S. fragilis had a smaller leaf area and epidermal cells, thicker palisade tissue, smaller lumen of main vein vessels, and a higher percentage of main vein xylem. S. fragilis had more distinctive xeromorphic characteristics in the lamina structure. Increased concentrations of Cd led to significant structural changes, mainly in the main vein. When searching for valid parameters in assessing plant to be utilized in phytoremediation, it is necessary to take into consideration the interrelation of a large number of micromorphological parameters together with physiological and biochemical characteristics.

Termite infestation is one of the fundamental problems associated with the loss of urban trees and ecological services. However, no such study has been performed in Pakistan to investigate the termite occurrence and assess such damages to urban trees caused by termites. For Lahore, research and comparable data on urban tree damages are rare or missing. This study surveyed six different microhabitats, including Bagh-e-Jinnah, canal vegetation, Model Town Park, Jallo Forestry, Race-Course Park, and FC College Vegetation employing the three belt transects (100 × 5 m) method. We geo-referenced termite-infested trees to investigate the termite occurrence on living and dead standing trees, termite diversity, and the assessment of tree damage by termites’ attack. We recorded four termite species (Odontotermes obesus Rambur, Coptotermes heimi Wasmann, Heterotermes indicola Wasmann, and Microtermes obesi Holmgren) representing two families (Rhinotermitidae and Termitidae). However, the diversity indices revealed that O. obesus (higher termite) and C. heimi (lower termite) were dominant with 46.60 and 36% of occurrence among observed trees, respectively. Kernel density function indicated that the Lahore Canal and Bagh-e-Jinnah plantation shared all four termites’ infestation evenly compared to other study sites. We observed the maximum number of damaged trees by termites in canal vegetation with the most damaged exotic tree species Populus euramericana along the canal green belt. Additionally, we observed significant (P < 0.05) termite-tree interactions with exotic, living, and dead standing tree species and found termite colony size positively (R = 0.985) correlated with the tree trunk diameter up to breast height (DBH). The average population of termites per unit volume of deadwood log was (0.39/cm³) within all plantation sites. In conclusion, this study provides simple, reckless, and inexpensive knowledge about the assessment of termite damage to trees, which may give a better idea in making decisions on tree selection and management in urban ecosystems.

This study aimed at assessing the effect of nitrogen addition under two forms, nitrate and ammonium, on the stabilization of Zn, Pb, and Cd by Populus euramericana Dorskamp grown in contaminated soils for 35 days under controlled conditions. Temporal changes in the soil pore water (SPW) were monitored for pH, dissolved organic carbon (DOC), and total dissolved concentrations of metals in the soils rhizosphere. Rhizospheric SPW pH decreased gradually with NH₄ ⁺ addition and increased with NO₃ ⁻ addition up to one unit, while it slightly decreased initially then increased for the untreated control soil DOC increased with time up to six times, the highest increase occurring with NH₄ ⁺ fertilization. An increase in the metal concentrations in the rhizospheric SPW was observed for NH₄ ⁺ addition associated with the lowest rhizospheric SPW pH, whereas the opposite was observed for the control soil and NO₃ ⁻ fertilization. Fertilization did not affect plant shoots or roots biomass development compared to the untreated control (without N addition). Metals were mostly accumulated in the rhizosphere and N fertilization increased the accumulation for Zn and Pb while Cd accumulation was enhanced for NH₄ ⁺ addition. Collectively, our results suggest metal stabilization by P. euramericana Dorskamp rhizosphere with nitrogen fertilization and are potential for phytostabilization of contaminated technosol.

Introduction Field experiments at the Shenyang Experimental Station of Ecology were conducted to study the adsorption, accumulation, and remediation of heavy metals by poplar and larch grown in artificially contaminated soil. Materials and methods The soil was spiked with a combination of Cd, Cu, and Zn at concentrations of 1.5, 100, and 200 mg·kg⁻¹, respectively. Results The results showed that the biomass of poplar (Populus canadensis Moench) was lower by 26.0% in the soil spiked with a mixture of Cd, Cu, and Zn, compared with the control. Concentrations of Cd in poplar leaf and Cu in poplar roots in the treated soil were 4.11 and 14.55 mg kg⁻¹, respectively, which are much greater than in corresponding controls. The migration of heavy metals in woody plant body was in the order Cd > Zn > Cu. Poplar had higher metal concentrations in aboveground tissues and a higher biomass compared with larch of the same age and therefore is potentially more suitable for remediation. In the heavy metal-polluted soil of this study, phytoremediation by poplar may take 56 and 245 years for Cd and Cu, respectively, for meeting the soil standards of heavy metals, and the corresponding phytoremediation times by larch would take 211 and 438 years. Conclusion The research findings could be used as a basis to develop ecological engineering technologies for environmental control and remediation of pollution caused by heavy metals in soils.