Topographical structures in planting design of living walls affect their ability to immobilise traffic-based particulate matter.

Traffic-generated particulate matter (PM) pollution is a serious threat to human health and the environment, especially in urban settings. Recent studies have revealed the effectiveness of living walls in the reduction of this pollution; these systems use variable planting designs and their topographical dynamics might have an impact on PM dry deposition. This present study, employing an experimentally manipulable living wall system using box (Buxus sempervirens L.) plants, examined whether plants arranged in a design with heterogeneous topography have a differential PM removal capacity compared to plants in a design with homogenous topography. Two planting designs using 'short' and 'tall' plants, were simultaneously used on this living wall and equally exposed to traffic-based PM for 5 consecutive days. PM accumulation on leaves was estimated using an Environmental Scanning Electron Microscope and ImageJ image analysis software. The experiment was replicated four times changing the position of each design on the wall, and any variation in PM capture levels on leaves belonging to different designs were identified using a Generalised Linear Mixed-effect Models (GLMM). The planting design with topographical heterogeneity resulted in significantly higher PM densities (PM10, PM2.5 and PM1) on leaf surfaces compared to a design with homogenous topography, indicating that topographical heterogeneity has a strong positive impact on the ability of plants to immobilise PM.

Quantification of the traffic-generated particulate matter capture by plant species in a living wall and evaluation of the important leaf characteristics.

Traffic-generated particulate matter (PM) is a significant fraction of urban PM pollution and little is known about the use of living walls as a short-term strategy to reduce this pollution. The present study evaluated the potential of twenty living wall plants to reduce traffic-based PM using a living wall system located along a busy road in Stoke-on-Trent, UK. An Environmental Scanning Electron Microscope (ESEM) and ImageJ software were employed to quantify PM accumulation on leaves (PM1, PM2.5 and PM10) and their elemental composition was determined using Energy Dispersive X-ray (EDX). Inter-species variation in leaf-PM accumulation was evaluated using a Generalized Linear Mixed-effect Model (GLMM) using time as a factor; any differential PM accumulation due to specific leaf characteristics (stomatal density, hair/trichomes, ridges and grooves) was identified. The study showed a promising potential for living wall plants to remove atmospheric PM; an estimated average number of 122.08 ±â€¯6.9 × 107 PM1, 8.24 ±â€¯0.72 × 107 PM2.5 and 4.45 ±â€¯0.33 × 107 PM10 were captured on 100 cm2 of the living wall used in this study. Different species captured significantly different quantities of all particle sizes; the highest amount of all particle sizes was found on the leaf-needles of Juniperus chinensis L., followed by smaller-leaved species. In the absence of an apparent pattern in correlation between PM accumulation and leaf surface characteristics, the study highlighted the importance of individual leaf size in PM capture irrespective of their variable micro-morphology. The elemental composition of the captured particles showed a strong correlation with traffic-based PM and a wide range of important heavy metals. We conclude that the use of living walls that consist largely of smaller-leaved species and conifers can potentially have a significant impact in ameliorating air quality by removing traffic-generated PM pollution to improve the wellbeing of urban dwellers.

The effect of winter stress on Ilex aquifolium L.previously fumigated with ozone.

European Holly (Ilex aquifolium) received either charcoal-filtered air (CFA) or CFA with 70 nl l(-1) ozone added for 7 h day(-1) over a 28 day period. Plants were then transferred into cooling incubators for hardening (4 degrees C day/2 degrees C night; day length 12 h) for 7 days and then to the frosting stage (2 degrees C day and -5, -10 or -15 degrees C night) for 4 days. The plants were then placed in ambient conditions. Treatment produced significant differences in chlorophyll fluorescence data. Stomatal conductance was significantly higher for the ozone treatments though both showed a general decline over all temperature regimes. Ozone also significantly increased electrolyte leakage and reduced winter survival. These results show that ambient concentrations of ozone can reduce the tolerance of I. aquifolium to freezing stress, which may have serious implications for its establishment and survival.

Ozone induced leaf loss and decreased leaf production of European Holly (Ilex aquifolium L.) over multiple seasons.

European Holly (Ilex aquifolium L.) was used to study the impact of one short (28 day) ozone fumigation episode on leaf production, leaf loss and stomatal conductance (g(s)), in order to explore potential longer term effects over 3 growing seasons. Young I. aquifolium plants received an episode of either charcoal-filtered air or charcoal-filtered air with 70 nl l(-1) O(3) added for 7 h d(-1) over a 28 day period from June 15th 1996, then placed into ambient environment, Stoke-on-Trent, U.K. Data were collected per leaf cohort over the next three growing seasons. Ozone exposure significantly increased leaf loss and stomatal conductance and reduced leaf production over all subsequent seasons. Impact of the initial ozone stress was still detected in leaves that had no direct experimental ozone exposure. This study has shown the potential of ozone to introduce long-term phenological perturbations into ecosystems by influencing productivity over a number of seasons.