High nitrogen addition decreases the ozone flux by reducing the maximum stomatal conductance in poplar saplings

Study of summer microclimate and PM2.5 concentration in campus plant communities

Understanding the influencing effect of meteorological factors and air pollutants in the campus plot and the relationship between them is an important topic in the planning and design of campus green space. The changes of pollutant concentrations and meteorological factors in campus green space have certain patterns and specific influencing factors. In this study, we selected four sample plots in Nanjing Forestry University as the research objects, and collected various environmental parameters of the four plots on July 25, 2022. The results showed that the main influences of meteorological factors are the type of the underlying surface of the site, the degree of plant canopy density and the shade coverage area of the building. These factors mainly have a great influence on the value of temperature and humidity. The comprehensive influencing factors can be concluded that the cooling and humidifying effect of the site is ranked as follows: forest > lawn > asphalt road > concrete Square. The main influencing factors of pollutants are: illumination, wind speed, temperature and relative humidity. Among them, illumination and temperature have a negative correlation with PM2.5, wind speed and relative humidity have a positive correlation with PM2.5. Our research shows that the adjustment of campus green space factors can reduce the concentration of pollutants by changing the meteorological factors.

Growth, ultrastructural and physiological characteristics of Abelmoschus cytotypes under elevated ozone stress: a study on ploidy-specific responses

Tropospheric ozone (O3 ) is a significant abiotic stressor whose rising concentration negatively influences plant growth. Studies related to the differential response of Abelmoschus cytotypes to elevated O3 treatment are scarce and need further exploration to recognise the role of polyploidisation in stress tolerance. In this study, we analysed the changes in growth pattern, ultrastructure, physiology and foliar protein profile occurring under O3 stress in Abelmoschus moschatus (monoploid), Abelmoschus esculentus (diploid) and Abelmoschus caillei (triploid). Our findings showed that higher stomatal conductance in A. moschatus triggered higher O3 intake, causing damage to stomatal cells and photosynthetic pigments. Additionally, it caused a reduction in photosynthetic rates, leading to reduced plant growth, total biomass and economic yield. This O3 -induced toxicity was less in diploid and triploid cytotypes of Abelmoschus . Protein profiling by sodium dodecyl sulpate-polyacrylamide gel electrophoresis showed a significant decrease in the commonly found RuBisCO larger and smaller subunits. The decrease was more prominent in monoploid compared to diploid and triploid. This study provides crucial data for research that aim to enhance plant ability to withstand O3 induced oxidative stress. Our findings may help in developing a tolerant variety through plant breeding techniques, which will be economically more advantageous in reaching the objective of sustainable production at the high O3 levels projected under a climate change scenario.

Response of tropical trees to elevated Ozone: a Free Air Ozone Enrichment study

Tropospheric ozone (O₃) has become one of the main urban air pollutants. In the present study, we assessed impact of ambient and future ground-level O₃ on nine commonly growing urban tree species under Free Air Ozone Enrichment (FAOE) condition. During the study period, mean ambient and elevated ozone (EO₃) concentrations were 48.59 and 69.62 ppb, respectively. Under EO₃ treatment, stomatal density (SD) significantly decreased and guard cell length (GCL) increased in Azadirachta indica, Bougainvillea spectabilis, Plumeria rubra, Saraca asoca and Tabernaemontana divaricata, while SD increased and GCL decreased in Ficus benghalensis and Terminalia arjuna. Proline levels increased in all the nine plant species under EO₃ condition. EO₃ significantly reduced photosynthetic rate, stomatal conductance (gs), and transpiration rates (E). Only A. indica and N. indicum showed higher gs and E under EO₃ treatment. Water use efficiency (WUE) significantly increased in F. benghalensis and decreased in A. indica and T. divaricata. Air Pollution Tolerance Index (APTI) significantly increased in Ficus religiosa and S. asoca whereas it decreased in B. spectabilis and A. indica. Of all the plant species B. spectabilis and A. indica were the most sensitive to EO₃ (high g_s and less ascorbic acid content) while S. asoca and F. religiosa were the most tolerant (lowg_s and more ascorbic acid content). The sensitivity of urban tree species to EO₃ is a cause of concern and should be considered for future urban forestry programmes. Our study should guide more such studies to identify tolerant trees for urban air pollution abatement.

Effects of elevated ozone on the uptake and allocation of macronutrients in poplar saplings above- and belowground

Ground-level ozone (O₃) is a secondary air pollutant and affects the roots and soil processes of trees. Therefore, O₃ can affect the uptake and allocation of nutrients in trees, which merits further clarification. A fumigation experiment with five O₃ levels was conducted in 15 open top chambers for two poplar clones, and the concentrations of six macronutrients (N, P, K, S, Ca, Mg) in different organs and leaf positions were determined. Under all O₃ levels, the concentration of mobile nutrients (N and P) was higher in upper leaves than in lower leaves, while the non-mobile nutrients (Ca and S) concentration was the opposite. Relative to charcoal filtered ambient air (CF), high O₃ treatment (NF60) significantly increased the concentration of mobile nutrients K and Mg in upper leaves by 38 % and 33 %, in lower leaves by 142 % and 65 %, respectively, which suggested the effect of O₃ on their concentrations was greater at the lower leaf position than at the upper leaf position. Elevated O₃ significantly increased the macronutrient concentrations in most organs. The effects of O₃ on nutrient concentrations were attributed using graphical vector analysis, suggested that the increase of nutrient concentration in the shoots was attributed to excessive nutrient stocks, while their increase in root was attributed to the "concentration" effect. Compared to CF, NF60 also reduced the root-to-shoot ratio of N, P, S, K, Ca and Mg stocks by 34 %, 39 %, 37 %, 64 %, 46 % and 42 %, respectively, indicating the allocation of increased nutrients to shoots in response to O₃ stress. Changes in the allocation pattern of nutrients in different leaf positions and organs of poplar were primarily in response to O₃ stress since these nutrients play important roles in some physiological processes. These results will help improve the plantation nutrient utilization by optimizing fertilizer management regimes under O₃ pollution.

Ozone Response of Leaf Physiological and Stomatal Characteristics in Brassica juncea L. at Supraoptimal Temperatures

Plants are affected by the features of their surrounding environment, such as climate change and air pollution caused by anthropogenic activities. In particular, agricultural production is highly sensitive to environmental characteristics. Since no environmental factor is independent, the interactive effects of these factors on plants are essential for agricultural production. In this context, the interactive effects of ozone (O3) and supraoptimal temperatures remain unclear. Here, we investigated the physiological and stomatal characteristics of leaf mustard (Brassica juncea L.) in the presence of charcoal-filtered (target concentration, 10 ppb) and elevated (target concentration, 120 ppb) O3 concentrations and/or optimal (22/20 °C day/night) and supraoptimal temperatures (27/25 °C). Regarding physiological characteristics, the maximum rate of electron transport and triose phosphate use significantly decreased in the presence of elevated O3 at a supraoptimal temperature (OT conditions) compared with those in the presence of elevated O3 at an optimal temperature (O conditions). Total chlorophyll content was also significantly affected by supraoptimal temperature and elevated O3. The chlorophyll a/b ratio significantly reduced under OT conditions compared to C condition at 7 days after the beginning of exposure (DAE). Regarding stomatal characteristics, there was no significant difference in stomatal pore area between O and OT conditions, but stomatal density under OT conditions was significantly increased compared with that under O conditions. At 14 DAE, the levels of superoxide (O2-), which is a reactive oxygen species, were significantly increased under OT conditions compared with those under O conditions. Furthermore, leaf weight was significantly reduced under OT conditions compared with that under O conditions. Collectively, these results indicate that temperature is a key driver of the O3 response of B. juncea via changes in leaf physiological and stomatal characteristics.