Photosynthetic Capacity, Stomatal Behavior and Chloroplast Ultrastructure in Leaves of the Endangered Plant Carpinus putoensis W.C.Cheng during Gaseous NO2 Exposure and after Recovery

Exogenous Salicylic Acid Alleviates NO2 Damage by Maintaining Cell Stability and Physiological Metabolism in Bougainvillea × buttiana 'Miss Manila' Seedlings

Exogenous substances can alleviate plant damage under adverse conditions. In order to explore whether different concentrations of salicylic acid (SA) can play a role in the resistance of Bougainvillea × buttiana 'Miss Manila' to nitrogen dioxide (NO2) stress and the relevant mechanisms of their effects, different concentrations of SA were applied locally under the control experiment condition of 4.0 μL·L-1 NO2, and the role of SA in alleviating injury was studied. The findings noted a significant increase in metabolic adaptations and antioxidant enzyme activities following 0.25-0.75 mM SA application (p < 0.05), except 1 mM. Superoxide dismutase (SOD) and catalase (CAT) in particular increased by 21.88% and 59.71%, respectively. Such an increase led to effective control of the reduction in photosynthetic pigments and the photosynthetic rate and protection of the structural stability of chloroplasts and other organelles. In addition, the activity of nitrate reductase (NR) increased by 83.85%, and the content of nitrate nitrogen (NO3--N) decreased by 29.23% in nitrogen metabolism. Concurrently, a principal component analysis (PCA) and a membership function analysis further indicated that 0.75 mM SA provided the most notable improvement in NO2 resistance among the different gradients. These findings suggest that 0.25-0.75 mM SA can relieve the stress at 4 μL·L-1 NO2 injury by effectively improving the antioxidant enzyme activity and nitrogen metabolizing enzyme activity, protecting the photosynthetic system and cell structure, but 1 mM SA had the opposite effect. In the future, the specific reasons for inhibition of SA at high concentrations and the comprehensive effects of the application of other exogenous compounds should be further studied.

Phytoremediation as a potential technique for vehicle hazardous pollutants around highways

With the synchronous development of highway construction and the urban economy, automobiles have entered thousands of households as essential means of transportation. This paper reviews the latest research progress in using phytoremediation technology to remediate the environmental pollution caused by automobile exhaust in recent years, including the prospects for stereoscopic forestry. Currently, most automobiles on the global market are internal combustion vehicles using fossil energy sources as the primary fuel, such as gasoline, diesel, and liquid or compressed natural gas. The composition of vehicle exhaust is relatively complex. When it enters the atmosphere, it is prone to a series of chemical reactions to generate various secondary pollutants, which are very harmful to human beings, plants, animals, and the eco-environment. Despite improving the automobile fuel quality and installing exhaust gas purification devices, helping to reduce air pollution, the treatment costs of these approaches are expensive and cannot achieve zero emissions of automobile exhaust pollutants. The purification of vehicle exhaust by plants is a crucial way to remediate the environmental pollution caused by automobile exhaust and improve the environment along the highway by utilizing the ecosystem's self-regulating ability. Therefore, it has become a global trend to use phytoremediation technology to restore the automobile exhaust pollution. Now, there is no scientific report or systematic review about how plants absorb vehicle pollutants. The screening and configuration of suitable plant species is the most crucial aspect of successful phytoremediation. The mechanisms of plant adsorption, metabolism, and detoxification are reviewed in this paper to address the problem of automobile exhaust pollution.

Elevated NO2 induces leaf defensive mechanisms in Bougainvillea spectabilis seedlings

With a growing economy, the living standard of people has improved which has led to increased use of urban motor vehicles globally. Consequently, the concentration of nitrogen dioxide (NO₂) has increased in the ambient air, becoming a major pollutant in urban areas. Plant leaves can absorb, adsorb and fix nitrogen oxides to some extent. Interestingly, NO₂ has been recognized as a positive/negative regulator of plant growth. To comprehensively understand the effect of NO₂-induced pollution on plants, Bougainvillea spectabilis seedlings were fumigated with different concentrations of nitrogen dioxide (NO₂) for a short period in the current study. Further, the induced morphological, physiological, and biochemical changes were measured in the treated as well as untreated seedlings. NO₂ exposure caused yellow-brown spotting on the leaf blades in B. spectabilis, which could be the symptoms of oxidative damage. Our findings also reflected the changes in antioxidant enzyme activity and peroxidation of membrane lipids. In addition, the levels of osmotic regulatory substances were also found to be altered to different degrees. In addition, the activities of nitrogen metabolism-related enzymes varied, mainly affecting amino acid metabolism. Overall, the current study would provide a theoretical and scientific basis for selecting and allocating plants in NO₂-contaminated areas to manage the pollutants level.

Urban conditions affect soil characteristics and physiological performance of three evergreen woody species

Physiological studies conducted mainly in metropolitan areas demonstrated that urban environments generate stressful conditions for plants. However, less attention has been paid to plant response to urban conditions in small cities. Here, we evaluated to what extent the health and physiological functions of some Mediterranean urban species [Quercus ilex L., Nerium oleander L. and Pittosporum tobira (Thunb.) W.T. Aiton] were impacted by urban and peri-urban conditions in Pisa (Italy), a small medieval city with narrow streets that impede efficient public transport causing oversized private transport. Experimental period spanned from late-summer to winter in concomitance with the sharp increase in air pollutants. Climate and air quality, soil physical and chemical properties, and plant physiological traits including leaf gas exchanges, chlorophyll fluorescence and leaf pigments were assessed. In soil, the organic carbon affected aggregates and water stability and the concentrations of some micro-elements decreased in winter. Air pollutants impaired leaf gas exchanges and photochemical processes at photosystem II, depending on species, season, and urban conditions. Shrubs were more susceptible than the tree species, highlighting that the latter adapted better to pollutants along an urban-peri-urban transect in Mediterranean environments. This study gives information on the physiological adaptability of some of the most frequent Mediterranean urban species to stressful conditions and demonstrated that, even in a small city, urban conditions influence the physiology and development of vegetation, affecting the plant health status and its ability to provide key ecosystem services.

Physiological and Molecular Analysis Reveals the Differences of Photosynthesis between Colored and Green Leaf Poplars

Leaf coloration changes evoke different photosynthetic responses among different poplar cultivars. The aim of this study is to investigate the photosynthetic difference between a red leaf cultivar (ZHP) and a green leaf (L2025) cultivar of Populus deltoides. In this study, ‘ZHP’ exhibited wide ranges and huge potential for absorption and utilization of light energy and CO₂ concentration which were similar to those in ‘L2025’ and even showed a stronger absorption for weak light. However, with the increasing light intensity and CO₂ concentration, the photosynthetic capacity in both ‘L2025’ and ‘ZHP’ was gradually restricted, and the net photosynthetic rate (Pn) in ‘ZHP’ was significantly lower than that in ‘L2025’under high light or high CO₂ conditions, which was mainly attributed to stomatal regulation and different photosynthetic efficiency (including the light energy utilization efficiency and photosynthetic CO₂ assimilation efficiency) in these two poplars. Moreover, the higher anthocyanin content in ‘ZHP’ than that in ‘L2025’ was considered to be closely related to the decreased photosynthetic efficiency in ‘ZHP’. According to the results from the JIP-test, the capture efficiency of the reaction center for light energy in ‘L2025’ was significantly higher than that in ‘ZHP’. Interestingly, the higher levels of light quantum caused relatively higher accumulation of Q_A^- in ‘L2025’, which blocked the electron transport and weakened the photosystem II (PSII) performance as compared with ‘ZHP’; however, the decreased capture of light quantum also could not promote the utilization of light energy, which was the key to the low photosynthetic efficiency in ‘ZHP’. The differential expressions of a series of photosynthesis-related genes further promoted these specific photosynthetic processes between ‘L2025’ and ‘ZHP’.

Comprehensive Transcriptome Analysis of Rare Carpinus putoensis Plants under NO2 stress

We evaluated a transcriptome using high-throughput Illumina HiSeq sequencing and related it to the morphology, leaf anatomy, and physiological parameters of Carpinus putoensis putoensis under NO₂ stress. The molecular mechanism of the C. putoensis NO₂ stress response was evaluated using sequencing data. NO₂ stress adversely affected the morphology, leaf anatomy, and total peroxidase (POD) activity. Through RNA-seq analysis, we used NCBI to compare the transcripts with nine databases and obtained their functional annotations. We annotated up to 2255 million clean Illumina paired-end RNA-seq reads, and 250,200 unigene sequences were assembled based on the resulting transcriptome data. More than 89% of the C. putoensis transcripts were functionally annotated. Under NO₂ stress, 1119 genes were upregulated and 1240 were downregulated. According to the KEGG pathway and GO analyses, photosynthesis, chloroplasts, plastids, and the stimulus response are related to NO₂ stress. Additionally, NO₂ stress changed the expression of POD families, and the HPL2, HPL1, and POD genes exhibited high expression. The transcriptome analysis of C. putoensis leaves under NO₂ stress supplies a reference for studying the molecular mechanism of C. putoensis resistance to NO₂ stress. The given transcriptome data represent a valuable resource for studies on plant genes, which will contribute towards genome annotations during future genome projects.

Physiological and biochemical responses of two precious Carpinus species to high-concentration NO2 stress and their natural recovery

Carpinus betulus and Carpinus putoensis are precious species in the world. Studies on the ecosystem function of the two species are rare. This study investigated the physiological and biochemical responses of C. betulus and C. putoensis to NO₂ stress and their natural recovery. C. betulus and C. putoensis seedlings underwent fumigation with 12.0 mg/m³ NO₂ for 0, 1, 6, 12, 24, 48, and 72 h, respectively. Then, the plants were allowed to recover at room temperature for 30 d. Physiological and biochemical changes in the leaves were compared between the two species. In terms of peroxidase (POD) activity, the damage response of C. betulus under NO₂ stress appeared later than that of C. putoensis. The soluble protein content of C. betulus was noticeably higher than that of C. putoensis, and C. betulus exhibited more stable membrane lipoperoxidation. The tendency of the changes in nitrate reductase of C. betulus was less noticeable than that of C. putoensis. The variation amplitudes of N, K, Mg, Zn and Mn in the leaves of C. putoensis were greater than those of C. betulus. C. putoensis showed more sensitive metabolisms in response to NO₂ stress compared with C. betulus. High-concentration NO₂ caused damage to C. betulus and C. putoensis was reversible, and both species returned to normal growth via their own metabolism after 30-d recovery. The results of this study may provide useful reference data for quantitative assessment of the ecosystem function of C. betulus and C. putoensis and for their scientific application in urban greening.