60 research outputs found
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Provision of ecosystem services by hedges in urban domestic gardens: focus on rainfall mitigation
In the UK urban context, domestic gardens are an important resource, taking up to 25% of an urban area, with hedges being their popular and widespread features. Garden hedges are able to provide a number of ecosystem services, including mitigation of rainfall, trapping of particulate pollution, local temperature regulation etc. Using hedges as a model, we argue that differences in plants’ capacity to provide environmental benefits should be taken into account, in addition to their suitability for particular conditions, ornamental appeal and cost, when choosing plants for green spaces. The overarching aim of our project is to quantify the simultaneous provision of multiple services by several widely used hedge species and cultivars. In this paper, we are focusing on the provision of rainfall capture by the hedges. The following species and cultivars, differing in the leaf and canopy structure and size, and in some physiological parameters, were chosen for the study: Photinia x fraseri 'Red Robin', Thuja plicata ‘Atrovirens’, Taxus baccata, Ligustrum ovalifolium ‘Aureum’ and ‘Argenteum’ and Cotoneaster franchetii. The experiments were conducted June-July 2015 in glasshouses at the University of Reading, UK. We measured the water use of different species/cultivars (6 plant ‘treatments’ and bare substrate as a control, in 10 L containers, with 6-8 replicates each) and their ability to hold water within the canopy. Plants’ leaf and root biomass and leaf area (LA) were also measured. Species/cultivars differed in the capacity of canopies to retain water after a simulated rainfall event. Ligustrum ‘Aureum’ held significantly more water within the canopy than other species/cultivars, despite not having the largest LA. Furthermore, when differences in LA were taken into the account, Cotoneaster, Thuja, Taxus and Ligustrum ‘Argenteum’ lost most water per unit leaf area suggesting that they have the greatest potential to restore soil’s capacity to receive subsequent rainfall. Our initial findings confirm the hypothesis that differences in plant structure and function lead to different capacities for rainfall capture. This could inform our planting choices and help to manage/reduce problems associated with excess rainfall
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Concept and methodology of characterising infrared radiative performance of urban trees using tree crown spectroscopy
Urban trees play an important role in cooling urban microclimates and regulating outdoor thermal comfort. To better understand their contribution to these processes, it is crucial to elucidate urban trees’ radiative thermal performance, especially in the infrared (IR) region (approximately 50% of solar radiation). Yet, owing to significant conceptual and methodological challenges, studies on the radiative performance of trees have mainly focused on individual leaves rather than crown-level characteristics. Here we applied a novel conceptual and methodological framework to characterise the crown-level IR radiative performance of 10 lime trees (Tilia cordata), a common urban tree in the UK and Europe. Our results show that reflected and transmitted solar energy from leaves is dominated (>70%) by IR radiation. At the leaf level, transmission and reflection spectra are similar between trees (differences typically 40% in IR region) were found between trees. These variations were largely due to crown structural differences (leaf number, density, angles), rather than leaf solar interaction character (leaf-level transmittance or reflectance, leaf colour). Crown transflectance measured from the four cardinal directions was significantly different in the IR region (maximum differences circa 30%), and changed substantially with solar time. Hence, a tree’s surroundings received very different, and time dependent, levels of solar IR radiation. These findings have significant implications for species selection and control of environmental stress factors in urban microclimates
Characterizing RecA-Independent Induction of Shiga toxin2-Encoding Phages by EDTA Treatment
Background: The bacteriophage life cycle has an important role in Shiga toxin (Stx) expression. The induction of Shiga toxin-encoding phages (Stx phages) increases toxin production as a result of replication of the phage genome, and phage lysis of the host cell also provides a means of Stx toxin to exit the cell. Previous studies suggested that prophage induction might also occur in the absence of SOS response, independently of RecA. Methodology/Principal Findings: The influence of EDTA on RecA-independent Stx2 phage induction was assessed, in laboratory lysogens and in EHEC strains carrying Stx2 phages in their genome, by Real-Time PCR. RecA-independent mechanisms described for phage l induction (RcsA and DsrA) were not involved in Stx2 phage induction. In addition, mutations in the pathway for the stress response of the bacterial envelope to EDTA did not contribute to Stx2 phage induction. The effect of EDTA on Stx phage induction is due to its chelating properties, which was also confirmed by the use of citrate, another chelating agent. Our results indicate that EDTA affects Stx2 phage induction by disruption of the bacterial outer membrane due to chelation of Mg 2+. In all the conditions evaluated, the pH value had a decisive role in Stx2 phage induction. Conclusions/Significance: Chelating agents, such as EDTA and citrate, induce Stx phages, which raises concerns due to their frequent use in food and pharmaceutical products. This study contributes to our understanding of the phenomenon o
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Can houseplants improve indoor air quality by removing CO2 and increasing relative humidity?
High indoor CO2 concentrations and low relative humidity (RH) create an array of well-documented human health issues. Therefore, assessing houseplants’ potential as a low-cost approach to CO2 removal and increasing RH is important.
We investigated how environmental factors such as ’dry’ ( 0.30 m3 m-3) growing substrates, and indoor light levels (‘low’ 10 µmol m-2 s-1, ‘high’ 50 µmol m-2 s-1 and ‘very high’ 300 µmol m-2 s-1), influence the plants’ net CO2 assimilation (‘A’) and water-vapour loss. Seven common houseplant taxa – representing a variety of leaf types, metabolisms and sizes – were studied for their ability to assimilate CO2 across a range of indoor light levels. Additionally, to assess the plants’ potential contribution to RH increase, the plants’ evapo-transpiration (ET) was measured.
At typical ‘low’ indoor light levels ‘A’ rates were generally low (< 3.9 mg hr-1). Differences between ‘dry’ and ’wet’ plants at typical indoor light levels were negligible in terms of room-level impact. Light compensation points (i.e. light levels at which plants have positive ‘A’) were in the typical indoor light range (1-50 µmol m-2 s-1) only for two studied Spathiphyllum wallisii cultivars and Hedera helix; these plants would thus provide the best CO2 removal indoors. Additionally, increasing indoor light levels to 300 µmol m-2 s-1 would, in most species, significantly increase their potential to assimilate CO2. Species which assimilated the most CO2 also contributed most to increasing RH
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Interaction between plant species and substrate type in the removal of CO2 indoors
Elevated indoor concentrations of carbon dioxide [CO2] cause health issues, increase workplace absenteeism and reduce cognitive performance. Plants can be part of the solution, reducing indoor [CO2] and acting as a low-cost supplement to building ventilation systems.
Our earlier work on a selection of structurally and functionally different indoor plants identified a range of leaf-level CO2 removal rates, when plants were grown in one type of substrate. The work presented here brings the research much closer to real indoor environments by investigating CO2 removal at a whole-plant level and in different substrates. Specifically, we measured how the change of growing substrate affects plants’ capacity to reduce CO2 concentrations. Spathiphyllum wallisii 'Verdi', Dracaena fragrans 'Golden Coast' and Hedera helix, representing a range of leaf types and sizes and potted in two different substrates, were tested. Potted plants were studied in a 0.15 m3 chamber under ‘very high’ (22000 lux), ‘low’ (~ 500 lux) and ‘no’ light (0 lux) in ‘wet’ (> 30 %) and ‘dry’ (< 20 %) substrate.
At ‘no’ and ‘low’ indoor light, houseplants increased the CO2 concentration in both substrates; respiration rates, however, were deemed negligible in terms of the contribution to a room-level concentration, as they added ~ 0.6% of a human’s contribution. In ‘very high’ light D. fragrans, in substrate 2, showed potential to reduce [CO2] to a near-ambient (600 ppm) concentration in a shorter timeframe (12 hrs, e.g. overnight) and S. wallisii over a longer period (36 hrs, e.g. weekend)
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Potential of urban roadside hedges for particulate matter removal – importance of species choice, and its economic impact
Urban hedges provide multiple ecosystem services including microclimate regulation, flood and pollution mitigation, and biodiversity provision. Their relatively compact nature may suit higher-density housing developments more readily than many other forms of green infrastructure. However, hedge plant species differ in their capacity to promote different services, so it is important that the decision to plant hedges is evidence-based. Our research focused on testing which hedge species (and which associated leaf and canopy properties) are required to maximise the capture and retention of airborne pollutant particles, which are harmful to human health. We collected leaf material from species with morphologically different leaves, located by major and minor roads in Reading (UK) after periods of dry summertime weather and analysed the quantities of deposited particulates. The species included hairy-leaved Cotoneaster franchetii Bois, waxy/smooth-leaved Acuba japonica Thunb. and Crataegus monogyna Jacq., along with coniferous Thuja plicata Donn ex. D. Don. Results show that hedges with hairy, rough, and oval leaves (e.g. Cotoneaster), best captured airborne particles. Results also suggest that a significant extent of coverage and hedge depth is required, particularly to reduce the concentration of fine particles and in species with smaller inherent capacity for particulates' capture. This is evidenced in similar concentrations of particulates we detected at the front and back of Crataegus and Thuja even when the hedge depth was in the 1.5-2 m range, suggesting that a greater hedge depth (and/or denser planting) is needed to reduce concentrations of fine particles. Furthermore, planting choice made a significant difference to the extent of capture only on major roads, where the pollutant concentrations are highest. Based on experimental measurements of particulates' capture we estimated the impact of planting 100 km of the best-performing species, Cotoneaster franchetii, in Reading over an appraisal period of 10 years. Results (central estimate) indicated that approximately £300,000 of health, environmental and economic damage costs to society could be avoided from road transport-associated PM10 and £15,000 of PM2.5 costs
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Careful plant choice can deliver more biodiverse vertical greening (green façades)
Plants growing against walls (green façades) are an important part of urban greening. We report on an experiment that used a set of replicated mini model building plots designed to quantify and compare potential biodiversity benefits associated with three plant species commonly grown as green façades in temperate climates: Hedera helix (common ivy) (either as a straight species, or a mix with H. helix ‘Glacier’), Parthenocissus tricuspidata (Virginia creeper) and Pileostegia viburnoides (climbing hydrangea). We assessed the relative abundance of invertebrates collected from green façades in Reading (UK), over two growing seasons. The abundance of invertebrates increased with wall vegetation depth and cover, where considerably more invertebrates were collected from vigorous/deeper leaf wall cover by Hedera helix compared to the other treatments. A combination of two ivy taxa showed a higher invertebrate abundance compared to H. helix alone. The experiment demonstrates that green façades on buildings provide resources for invertebrates; the more vegetation resources there are, and the more varied they are, the more invertebrates are supported. It is clear that green façades can add to the value of invertebrate abundance on buildings and that plant choice is a strong determining factor to that value
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