Plant selection for roadside rain gardens in cold climates using real-scale studies of thirty-one herbaceous perennials

Plant selection for rain gardens along streets and roads in cold climates can be complicated, as the plants are subjected to combined stresses including periodic inundation, de-icing salts, road dust, splashes of water from the road, freezing and thawing of soil, and periods with ice cover during the winter. The purpose of this study was to identify species suited to grow in these conditions and determine their optimal placement within roadside rain gardens. Thirty-one herbaceous perennial species and cultivars were planted in real-scale rain gardens in a street in Drammen (Norway) with supplemental irrigation, and their progress was recorded during the following three growing seasons. The study highlights considerable differences between species’ adaptation to roadside rain gardens in cold climates, especially closest to the road. Some candidate species/cultivars had a high survival rate in all rain garden positions and were developed well. These were: Amsonia tabernaemontana, Baptisia australis, Calamagrostis × acutiflora ‘Overdam’, Hemerocallis ‘Camden Gold Dollar’, Hemerocallis ‘Sovereign’, Hemerocallis lilioasphodelus, Hosta ‘Sum & Substance’, Iris pseudacorus and Liatris spicata ‘Floristan Weiss’. Other species/cultivars appeared to adapt only to certain parts of the rain garden or had medium tolerance. These were: Calamagrostis brachytricha, Carex muskingumensis, Eurybia × herveyi ‘Twilight’, Hakonechloa macra, Hosta ‘Francee’, Hosta ‘Striptease’, Liatris spicata ‘Alba’, Lythrum salicaria ‘Ziegeunerblut’, Molinia caerulea ‘Moorhexe’, Molinia caerulea ‘Overdam’, and Sesleria autumnalis. Species/cultivars that showed high mortality and poor development at all rain garden positions should be avoided in roadside cold climate rain gardens. These include Amsonia orientalis, Aster incisus ‘Madiva’, Astilbe chinensis var. tacquettii ‘Purpurlanze’, Chelone obliqua, Dryopteris filix-mas, Eurybia divaricata, Geranium ‘Rozanne’, Helenium ‘Pumilum Magnificum’, Luzula sylvatica, Polygonatum multiflorum and Veronicastrum virginicum ‘Apollo’. The study also found considerable differences between cultivars within the same species, especially for Hosta cvv. and Liatris spicata. Further investigations are needed to identify the cultivars with the best adaption to roadside rain gardens in cold climates.     

Plant selection for rain gardens: Response to simulated cyclical flooding of 15 perennial species

Plant selection for rain gardens can be complicated, as cyclic flooding and a gradient of moisture level are expected in the depression structure of a rain garden. However, few studies to date have quantified how plant establishment is affected by rain garden moisture dynamics. This study investigated tolerance of 15 candidate perennial species, which experienced flooding cycles consisting of 1-day and 4-day inundation and draining phases. In this study, detection of species suitability using survival and growth measurements coupled with the stress indicator (i.e. chlorophyll fluorescence) provided a valid framework for wider use in plant selection for rain gardens. The methodology is also confident in predicting the possible placing in different plant moisture zones. All species survived the cyclic flooding treatments and grew to their maximum. Photosynthesis and physical growth in only a few candidate species (e.g. Amsonia tabernaemontana var. salicifolia, Gaura lindheimeri, Sanguisorba tenuifolia ‘Purpurea’ and Thalictrum aquilegifolium) tended to be inhibited by treatments adopting 4-day cyclic flooding, whilst tolerance to 1-day cyclic flooding was clearly demonstrated in most species. Analysis suggests that most species assumed to withstand infrequent to periodic inundation, such as Iris sibirica, Filipendula purpurea and Miscanthus sinensis, are resilient species and are sensible for use in a wider range of rain garden moisture conditions from damp depression bottom to dry margin. Species assumed to be intolerant of inundation such as Gaura lindheimeri may be successful in the rain garden environment, but they are recommended for the dryer zones.     

Hydrological behaviour of rain gardens and plant suitability: A study in the Veneto plain (north-eastern Italy) conditions

Since spring 2011 the roof of a building on the Agripolis Campus of the University of Padova (Italy) has been used as a drainage area for two rain gardens with a circular area of about 10% and 20% of the drainage area respectively. To improve soil infiltration, the topsoil was removed up to the depth of 1 m and filled with a mix of 50% sand, 25% compost and 25% of the existing topsoil. Herbaceous perennials were selected and planted to test their adaptability to different soil water conditions in the rain garden. To evaluate the capacity of each rain garden to manage stormwater runoff a simplified water balance was done, estimating actual evapotranspiration using the WUCOLS method. From autumn 2012 runoff volumes were collected just from one pitch of the roof, and directed only into the smaller rain garden that became equal to 15% of the new roof drainage area. We thus had the possibility to test the functionality of rain gardens with three different percentages of roof drainage area: 10, 15 and 20%, even if in different periods. Results are presented relating to a four-year experimental period. Regarding hydrological behaviour, the input water volumes caused a slight overflow only during a few rainfall events. Consequently, the results showed a high capacity to manage stormwater runoff and also in the smaller rain garden almost the total roof runoff volumes infiltrated into the soil. As regards plants, the results indicated that the growth is affected by their position in the rain garden, from the wettest condition in the centre to the driest at the perimeter, except for Hemerocallis hybrida that showed great adaptability in all positions. Aster novi-belgii, Echinacea purpurea, Iris pseudacorus, Molinia caerulea and Rudbeckia fulgida also showed good adaptation, even if not in all rain garden zones, with highly aesthetic results. Lythrum salicaria and Saponaria officinalis plants appeared to be unsuitable for rain gardens. The results of the experiment have shown that, in the Veneto plain environment, rain gardens with a size of 10–15% of the roof drainage area can ensure both the sustainable management of stormwater runoff and a high aesthetic functionality.     

Long-term impact of road salt (NaCl) on soil and urban trees in Edmonton,Canada

The application of de-icing salts for winter road maintenance is recognized as a major contributor to the decline of urban trees. We conducted a long-term monitoring program across several locations in the City of Edmonton (Alberta, Canada) to evaluate the impact of roadway salt application on tree species widely planted in boulevards and right-of-ways: Ulmus americana, Fraxinus pennsylvanica, Pinus contorta, and Picea glauca. Soil and leaf samples were collected from a total of 16 sites over six years. There were four sites selected for each tree species: three mid- to high- traffic roadside sites that received regular winter maintenance and one non-serviced site (control). Sampling was performed three times per year from late spring to late summer. Airborne salinity was assessed in four locations at different distances from the road. In 50% of the roadside sites, soil electrical conductivity (EC) values exceeded 2 dS m⁻¹. Soil pH in all of the roadside sites was also significantly higher than in the control sites, with values ranging from 7.6 to 8.5. In all four species, trees growing in sites with high soil EC had increased leaf Na concentrations and reduced leaf chlorophyll concentrations. Among the airborne monitoring sites, Na deposition in high traffic locations was over four-fold higher than those measured in the control location. Furthermore, Na levels remained relatively high at 20–50 m from the main road. Our data suggest that while soil salinity is among the main stressors affecting roadside trees in Edmonton, salt spray deposition may also have a significant impact on trees located close to high vehicle traffic areas and dense road networks. Our study highlights the importance of collecting data over several years and from multiple locations to account for the spatial and temporal heterogeneity of the urban environments in order to better evaluate the impact of road salt application on urban trees.     

The domestic garden – Its contribution to urban green infrastructure

Domestic gardens provide a significant component of urban green infrastructure but their relative contribution to eco-system service provision remains largely un-quantified. ‘Green infrastructure’ itself is often ill-defined, posing problems for planners to ascertain what types of green infrastructure provide greatest benefit and under what circumstances. Within this context the relative merits of gardens are unclear; however, at a time of greater urbanization where private gardens are increasingly seen as a ‘luxury’, it is important to define their role precisely. Hence, the nature of this review is to interpret existing information pertaining to gardens/gardening per se, identify where they may have a unique role to play and to highlight where further research is warranted. The review suggests that there are significant differences in both form and management of domestic gardens which radically influence the benefits. Nevertheless, gardens can play a strong role in improving the environmental impact of the domestic curtilage, e.g. by insulating houses against temperature extremes they can reduce domestic energy use. Gardens also improve localized air cooling, help mitigate flooding and provide a haven for wildlife. Less favourable aspects include contributions of gardens and gardening to greenhouse gas emissions, misuse of fertilizers and pesticides, and introduction of alien plant species. Due to the close proximity to the home and hence accessibility for many, possibly the greatest benefit of the domestic garden is on human health and well-being, but further work is required to define this clearly within the wider context of green infrastructure.     

The impact of rainfall in remobilising particulate matter accumulated on leaves of four evergreen species grown on a green screen and a living wall

Green walls have recently been identified as a green infrastructure (GI) solution to the problem of particulate matter (PM) air pollution. Green wall systems mostly use evergreen plants as the leaves are retained throughout the year; however, researchers have argued that evergreen foliage becomes saturated with PM and fails to capture more due to a long retention time on the leaves. This study evaluated the potential of (simulated) rainfall to remobilise these captured PM and renew the capture ability of the leaf surfaces of four evergreen species (Heuchera villosa Michx, Helleborus × sternii Turrill, Bergenia cordifolia (Haw.) Sternb., Hedera helix L.) used in a living wall and a green screen located along a busy road in Stoke-on-Trent, UK. The approach used compared PM densities on pre- and post-rain exposed leaf surfaces (using leaf halves of the same leaf) and using a paired t-test to identify any significant reduction in PM due to the rainfall. An Environmental Scanning Electron Microscope (ESEM) and ImageJ image analysis software were employed to quantify the PM densities on leaves. The reduction of PM on leaves, following exposure to 16 mm hr⁻¹ simulated rain in six different rainfall durations was estimated in all four species in order to evaluate any variable impact of rainfall on different species of plants. PM wash-off levels on leaves of H. helix by 41 mm hr⁻¹ rain was also evaluated, using the same rainfall durations, to assess any differential impact of rainfall intensity on PM wash-off. This study revealed a significant impact of rainfall in washing the particles off the leaves in all rainfall durations used. A one-way Anova in a Generalised Linear Model showed a differential impact of rainfall in remobilising PM on different species of plants. The rainfall with higher intensity (41 mm hr⁻¹) showed a significantly higher impact on PM wash-off compared to 16 mm hr⁻¹ rain. The results of this study demonstrated the potential of green walls to act as good PM traps throughout the year by recycling their capture surfaces.     

Reponses of mamey sapote (Pouteria sapota) trees to continuous and cyclical flooding in calcareous soil

Physiological and growth responses of ‘Pantin’ and ‘Magana’ mamey sapote (Pouteria sapota) trees to continuous and cyclical flooding were studied in a series of experiments. Trees were grown in containers in a very gravelly loam soil and were subjected to continuous flooding of the root zone for 30–66 days (Experiments 1 and 2) or alternating flooding–unflooding cycles for 50 days (Experiments 3–5). For all experiments, the control treatment consisted of nonflooded trees. Net CO₂ assimilation (A) and stomatal conductance (g_s) decreased within 3 days of continuous flooding and internal CO₂ concentration was significantly higher in leaves of flooded than nonflooded plants. In the cyclic flooding experiments, trees were flooded in 3- to 6-day cycles and then unflooded for the same time periods. Stomatal conductance and A decreased within 3 days of flooding, leaf epinasty occurred between days 5 and 10, leaf senescence and abscission occurred between days 15 and 30, and branch dieback and tree death occurred between days 30 and 60. Three cycles of 3-day flooding and 3-day recovery of trees had little effect on leaf gas exchange of ‘Magaña’ trees. Similarly, ‘Pantin’ trees survived 3 cycles of 6 days of flooding interspersed with 3–6 days of recovery despite consistent decreases in g_s and A during flooding. Stomatal conductance and A of both mamey sapote cultivars decreased within a few days of flooding and this species appears to have intermediate flooding tolerance compared with other tropical fruit crops based on tree survival.     

Winter protection of container-grown nursery stock as affected by container design,hardening-off time and solar exposure

The effects of container type (round vs. square), solar exposure (100% vs. 50%) and hardening-off time (0, 3 or 6 weeks) on winter damage to Ilex crenata Thumb. ‘Hetzii’ (Hetz Japanese holly) and Buxus sempervirens L. (common boxwood) were studied. Container type and hardening-off time had significant effects on plant viability of Ilex crenata ‘Hetzii’ after exposure to freezing temperatures. Plants in square containers achieved substantially higher viability ratings than plants in round containers after freezing. Buxus sempervirens was significantly affected by hardening-off time only. Plant viability increased greatly with 3 or 6 weeks of hardening-off as compared to no hardening-off. Common boxwood plants in square containers did not achieve the same level of growth as plants in round containers during the 1980 growing-season (before freezing). Optimum growth for Buxus sempervirens occurred under full solar exposure.     

Stability of landscape trees in engineered and conventional urban soil mixes

Urban trees are frequently exposed to unsuitable soil conditions that can hamper root system development, potentially affecting both tree health and stability. Engineered soil designs have been developed to increase soil volume for trees planted in confined spaces, and past research has shown that these designs improve growing conditions. However, tree stability in these engineered soils has received limited attention from researchers. In this study, we evaluated the stability of two tree species of contrasting soil quality tolerance (Prunus serrulata and Ulmus parvifolia) after 3 years growth in two skeletal soil mixes, in a suspended pavement design (uncompacted soil), and in a conventionally prepared soil pit. Tree stability was evaluated by measuring trunk resistance to a lateral deflecting force applied with a rope winch system under both ambient and near-saturated soil conditions. Although heavily irrigating the experimental soils had no effect on tree stability, species-specific responses to soil mixes were observed. P. serrulata grown in the gravel-based skeletal soil showed greater trunk deflection resistance than trees grown in the other soil treatments, yet the stability of U. parvifolia was unaffected by soil type. These species-specific responses were consistent with earlier observations of root development in which P. serrulata grew up to 60 times greater root length in gravel-based skeletal soil whereas U. parvifolia root growth was similar in all soil treatments. This research provides evidence that certain tree species planted in conventional tree pits may be more prone to uprooting due to poor root development and that root anchorage might be improved for these species by utilizing a skeletal soil mix.     

How good are containerized trees for urban cooling?

The capacity of urban trees in mitigating urban heat is well-known. As space is often limited, one feasible option for increasing the urban green would be containerized plants. Nevertheless, for optimizing the vitality and benefits, detailed knowledge on tree growth reactions in different types of containers is missing. We designed an experiment with two commonly planted but ecologically contrasting urban tree species Tilia cordata and Platanus x hispanica planted into the ground and in containers according to four different planting types, with or without drought stress. Along with the meteorological variables, continuous soil moisture and temperature at 25 cm depth, sap flow, as well as measurements of leaf physiological responses i.e. stomatal conductance, mid-day leaf water potential and chlorophyll content were measured three times on sunny and warm summer days during 2020 and 2021. P. hispanica showed more than double diameter increment at breast height in the ground than in containers; however, the growth trend was relatively better for T. cordata in containers. While comparing different container types and species reactions, it was clear that soil temperature within the plastic containers were significantly higher, whereas insulation is not enough to reduce either the temperature or slowing down the soil drying out. Where both the species showed lower stomatal control over atmospheric demand, P. hispanica showed leaf transpiration energy loss of around 300 W m⁻² when planted in the ground and T. cordata trees around 260 W m⁻² when planted in non-insulated containers, which are comparable to the energy loss from the street trees. Therefore, a strategy of mixed planting with faster growing species such as P. hispanica that provide stronger cooling at the initial stage in the containers to be complemented and eventually replaced with medium growing species T. cordata for relatively longer time period could be suggested.     

Diurnal and seasonal changes in the xylem water potentials of Grevillea and Myoporum plants during drought

Summary

Drought is an irregular feature of World climate and has adverse effects on ornamental plants growing in urban environments. Grevillea ‘Moonlight’ and Myoporum elipticum are attractive native Australian species that are commonly used in parks and gardens and are generally regarded as being drought-tolerant. Diurnal and seasonal water relations during a drought cycle of G. ‘Moonlight’ and M. elipticum, growing together in a non-irrigated garden bed, were monitored during a Summer (wetter)-to-Winter (dryer) transition period using a pressure chamber. G. ‘Moonlight’ generally maintained higher xylem water potentials than M. elipticum. Pre-dawn xylem water potentials in drought-affected M. elipticum dropped to around –2.5 MPa, while G. ‘Moonlight’ maintained pre-dawn xylem water potentials of around –1.0 MPa. This difference suggests that, because pre-dawn xylem water potentials reflect soil water potentials, G. ‘Moonlight’ accessed a different or additional source of soil water to M. elipticum. This study demonstrates the utility of the pressure chamber for describing the diurnal and seasonal water relations of ornamentals in a mixed planting in urban horticulture.     

Successful creation of species-rich grassland on road verges depend on various methods for seed transfer

This study focused on a suite of vascular plant species (six herbs and two grasses) common to traditionally managed, species-rich grasslands in Western Norway. We assessed the suitability of two species transfer methods (seed sowing and soil seed bank) for restoration of species-rich grassland on a newly established road verge. We compared the species' frequencies one and three years after they were sown on a naked, newly created road verge with their frequencies in aboveground vegetation and soil seed banks of comparable, local grasslands. Species frequencies in the aboveground vegetation differed significantly from those in the seed banks. Moreover, the frequencies in the seed banks differed from those recorded one year after sowing, and the frequencies in the aboveground vegetation differed from those recorded three years after sowing. Avenula pubescens and Knautia arvensis, found in more than 25% of the aboveground grassland plots, did not germinate from any of the seed bank samples. Festuca rubra, Galium verum, Pimpinella saxifraga and Silene vulgaris were more frequent in the aboveground plots than in the seed bank samples. Pimpinella saxifraga, Galium verum and Lychnis viscaria emerged quite well both from sown seeds and from the seed bank. Avenula pubescens was frequent in the aboveground vegetation, but did not germinate from sown seeds. Six species established well from seeds, and most increased in frequency in the sown plots from the first to the third year. No species was found in the sown plots only, but three years after sowing, three species were more frequent in the sown plots than in the aboveground vegetation of donor grassland plots. Our fine-scale, point-to-point study demonstrates that different restoration methods produce widely differing species composition even when the donor material is identical. We propose that different substrates and a combination of establishment methods (sowing and hay transfer) are needed as supplements to seed banks to re-establish species-rich grassland.     

Leaf gas exchanges and photosystem efficiency of the holm oak in urban green areas of Florence,Italy

In urban environments, trees are often faced with limiting physical factors at above- and below-ground levels. These factors include poor air quality, and water and soil pollution that may differ substantially from the natural environment. While numerous studies on urban climate and floristic analyses have been published, studies on the physiological performance and growth of trees in urban sites are rather scarce. They are often in contradiction with the general opinion of the growth's constraint. Generally, it is recognized that urban soils are made of poor landfill materials hampering soil water retention. Often, the soil is sealed by asphalted surfaces that prevent rain infiltration. Nevertheless, there is a gap of information to support the hypothesis by which such conditions determine plant water stress. This study will analyze the water relations and the performance of photosynthesis of Quercus ilex exemplars growing in three different conditions of urban green areas (urban park, outskirt/countryside and urban road) in the city of Florence (Italy) conducted in the year 2002. Results have evidenced a decline in photosynthetic rate in all three sites but a certain capacity of Q. ilex to acclimate to the harsh conditions of urban roads in terms of water relations, tissue elasticity and in photosystem efficiency that was higher at the beginning of summer.     

Mixtures of crushed rock, forest soils, and sewage sludge used as soils for grassed green areas

In two container experiments, we evaluated mixtures of crushed rock, forest soil, and sewage sludge for use as growth media in green areas. We applied two types of crushed rock (0–2 mm fraction), two forest soils (sandy loam), and limed sewage sludge (pH 10), and studied the growth of ryegrass (Lolium multiflorum var. westervoldicum) during one growing season.Including ≥0.2 m³ m⁻³ sewage sludge in the soil mixtures initially inhibited growth, presumably due to toxic levels of ammonium-N. Up to 0.25 m³ m⁻³ sludge increased the total yield of ryegrass, but at a level as low as 0.1 m³ m⁻³, more nutrients were available than could be taken up by the crop. At present, up to 0.3 m³ m⁻³ sewage sludge is allowed in soil mixtures used in green areas in Norway, although that level should probably be lowered due to the risk of abnormal (enhanced or inhibited) plant growth, and leaching of nutrients. We recommend a maximum of 0.1 m³ m⁻³ when applying the kind of sludge used in our experiments.All mixtures containing acid forest soil gave better results than those comprising slightly alkaline forest soil. The best mixture for ryegrass was crushed rock and acid forest soil at a ratio of 1:2. Compared to pure acid forest soil ryegrass grew equally well or better on mixtures containing ≥0.50 m³ m⁻³ acid forest soil. The differences in growth between the various soil mixtures were due to texture and physical properties, and to dissimilarities in the effects of sewage sludge on mineralisation of nitrogen in the mixtures comprising acid and slightly alkaline forest soil.     

The use of native turf mixtures to approach sustainable lawn in urban landscapes

Native grasses are excellent candidate species for manipulation to produce dwarf and turf type varieties as well as for producing cultivars with higher attractiveness and requiring less maintenance to be used as a turf grass in arid and semi-arid regions of the world. This investigation was conducted to explore visual qualities of native grasses and their mixtures compared to commercial turf. The field experiment was set out in a split-plot in time based on a randomized experimental design with three replications. We used two native monoculture accessions, perennial ryegrass (Lolium perenne L. ‘Yarand’) and (Lolium perenne L. ‘Shadegan’), Native low-variety Mixture (NM1): consisting of 50% Lolium multiflorum ‘Shadegan’? 50% Festuca spp. ‘Shadegan’, Native high-variety Mixture (NM2): consisting of 55% Lolium perenne L. ‘Yarand’? 35% Lolium perenne L. ‘Shadegan’? 5% L. multiflorum ‘Shadegan’ and 5% Festuca spp. ‘Shadegan’ and compared this with one commercial turf mixture that is commonly used in landscaping. Results indicated the effects of seasons and turf grass types and their interaction had significant effects on most variables including quality, season color, leaf texture, density, quality after clipping (p < 0.01). The visual quality measurements indicated the superiority of L. perenne ‘Shadegan’ over other native monoculture and polyculture and its ablility to compete with the commercial turf. The native turf mixture of NM2 showed several good characteristics. L. perenne ‘Yarand’ had statistically the lowest score for visual appeal as compared with the other turf types. This research suggests that the use of native grass species of L. perenne ‘Shadegan’ is worth investigating for better performance of the native landscape.     

Yarrow (Achillea millefolium) for low-input lawns in the Mediterranean environment

In recent years, environmental concerns have created a desire for the sustainable care of grass swards, with a specific goal of reducing resources needed for turfgrass maintenance by utilising low-input species best adapted to specific local environmental conditions. A two-year field experiment was conducted to compare the aesthetic or ornamental quality, and function potential, of different swards. The treatments consisted of four monostands of white clover (Trifolium repens L.), yarrow (Achillea millefolium L.), strong creeping red fescue (Festuca rubra L. ssp. rubra Gaudin), and tall fescue (Festuca arundinacea Schreb. = Schedonorus arundinaceus Schreb. Dumort.), three two-species mixtures of white clover + yarrow, white clover + strong creeping red fescue, and yarrow + strong creeping red fescue, and one three-species mixture of white clover + yarrow + strong creeping red fescue. Within each plot, a botanical survey was performed each spring to estimate species relative abundance by determining the proportions of different species present. All plots were evaluated every two weeks during the growing period for visual quality and normalised difference vegetative index. Vegetation canopy height in each plot was measured before each biweekly mowing event, and clippings were collected to measure vegetative dry matter. Relative abundance of yarrow, strong creeping red fescue, and tall fescue was stable throughout the entire study period. The mixtures including yarrow displayed sufficient or higher quality ratings (≥6) in all seasons with the exception of winter, however, yarrow + strong creeping red fescue compensated each other's defects by maintaining their relative abundance (≥ 80%) over time as well suppressing or prevent significant weed invasion (relative abundance <15%). Moreover, yarrow or strong creeping red fescue monostands, or yarrow + strong creeping red fescue could be maintained with lower number of mowing events, due to their lower vertical growth. In conclusion, alternative plant species to turf-type grasses produced a visual quality equal to or better than tall fescue maintained under low fertilisation and mowing frequency. All swards that included yarrow produced better visual quality, exhibited better weed control, had lower vertical growth rate, and provided an aesthetically pleasant, persistent, and sustainable vegetative ground cover than other swards, and can be utilised as a low-input species.     

Effects of foliar-applied nitrogen during winter on growth,nitrogen content and production of passionfruit

The effects of foliar-applied nitrogen (11.5 g N l⁻¹) during winter on growth, nitrogen content and production of passionfruit (Passiflora edulis f. edulis × P. edulis f. flavicarpa cultivar E-23 grafted onto P. edulis f. flavicarpa) was investigated in subtropical Queensland, Australia. Vegetative growth and flowering were severely restricted during winter in the untreated vines, despite the maintenance of leaf nitrogen levels within the range presently believed to be optimum for Queensland conditions after nitrogen was applied to the soil in autumn. Foliar urea applications during winter (monthly or twice monthly) increased leaf nitrogen levels but reduced growth and subsequent fruitlet number.Reductions in vegetative growth during winter in passionfruit appear to be due to a direct effect of cool soil and/or air temperatures, unrelated to nitrogen uptake, translocation and leaf nitrogen level.     

Dimensional and genetic characterization of the last oriental plane trees (Platanus orientalis L.) of historical sites in Lazio (central Italy)

In central Italy, Platanus orientalis L. specimens characterize many gardens in urban and suburban villas. In this research, centuries-old oriental plane trees were studied in different historical sites of Lazio according to the COVE (COnservation of VEteran trees) multidisciplinary model. Historical sources, morphological and dendrometric aspects, crown quality, genetic traits of each specimen, as well as their susceptibility to the canker stain disease, were investigated. Platanus orientalis was clearly distinguished from P. occidentalis and their hybrid P. acerifolia through molecular tools. UPGMA analysis based on SSR and ISSR molecular markers clustered the plane trees in different sub-groups, probably according to the different sites of sampling. These findings, supported by historical and morphological data collected in the considered sites, showed that almost all the trees studied are a small remnant of those planted in the period running from the second half of XVI century to the first decades of XVII century. Plant health conditions diverge within and among the sites inspected. Past-prolonged severe pruning treatments of trees located near the main monuments affected their growth, causing faster and premature senescence. However, the management of historical gardens has so far led to an efficient prevention of Ceratocystis platani introduction, spread and establishment. This study highlights the importance of a multidisciplinary approach to interpret the present status of the ancient tree asset within historical sites and let the past become a lesson for the future in a broader scenario of conservation and management of cultural heritage.     

Influence of no-tillage and organic mulching on tomato (Solanum Lycopersicum L.) production and nitrogen use in the mediterranean environment of central Italy

In conservation tillage systems based on legume mulches it is important to optimize N management strategies. The present study evaluated the effect of some winter legume cover crops converted into mulches on the following no-tillage tomato (Solanum Lycopersicum L.) yield, tomato nitrogen uptake, tomato use efficiency (NUE), soil nitrate and the apparent N remaining in the soil (ARNS) in a Mediterranean environment. Field experiments were carried out from 2002 to 2004 in a tomato crop transplanted into: four different types of mulches coming from winter cover crops [hairy vetch (Vicia villosa Roth.), subclover (Trifolium subterranem L.), snail medic (Medicago scutellata L. Miller), and Italian ryegrass (Lolium multiflorum Lam.)]; a conventional tilled soil (CT); and a no-tilled bare soil (NT). All treatments were fertilized with three different levels of nitrogen (N) fertilizer (0, 75, and 150 kg N ha⁻¹). Cover crop above-ground biomass at cover crop suppression ranged from 4.0 to 6.7 t ha⁻¹ of DM and accumulated from 54 to 189 kg N ha⁻¹, hairy vetch showed the highest values followed by subclover, snail medic and ryegrass. The marketable tomato yield was higher in no-tilled legume mulched soil compared to no-tilled ryegrass mulched soil, CT, and NT (on average 84.8 vs 68.7 t ha⁻¹ of FM, respectively) and it tended to rise with the increase of the N fertilization level. A similar trend was observed on tomato N uptake. Hairy vetch mulch released the highest amount of N during tomato cultivation followed by subclover, snail medic, and ryegrass (on average 141, 96, 90 and 33 kg N ha⁻¹). The tomato NUE tended to decrease with the increase of the N fertilization rates, it ranged from 39 to 60% in no-tilled legume mulched soil and from −59 to 30% in no-tilled ryegrass mulched soil when compared to the CT. The soil NO₃-N content and the ARNS was always higher in the soil mulched with legumes compared to the soil mulched with ryegrass and in NT and CT. This study shows that direct transplanting into mulches coming from winter legume cover crops could be useful for improving the yield and the N-uptake in a no-tillage tomato crop. Furthermore, considering the high N content in the upper soil layer and the remaining N content in the organic mulch residues after tomato harvesting, there is a large amount of N potentially available which could be immediately used by an autumn–winter cash crop.     

A study of chemical characteristics of soil in relation to street trees status in Riga (Latvia)

The chemical composition of soil and appropriate supply of nutrients are very important factors for normal plant growth and development. Lime tree (Tilia x vulgaris H.), is a popular tree species used for urban landscaping in Europe. However, there is little information on the chemical element concentrations available to and recommended for T. x vulgaris in urban soils. The objectives of this study were: (1) to investigate the amount of nutrients, de-icing salts and heavy metals available for uptake by trees in the city centre on a seasonal scale; and (2) to assess the relationship between the vitality of T. x vulgaris and soil chemistry. The research was carried out in five streets and a park in Riga (Latvia) during 2005–2007. Plant-available concentrations of 17 nutrients and heavy metals were determined via 1 M HCl extraction. Soil Cl content, pH, and electrical conductivity were also measured.The investigation revealed a high heterogeneity in soil chemical composition. In total, the element concentrations in urban soils did not exceed values commonly found in urban environments. Higher concentrations of Na, Cl, Ca, Mg, Zn, Cu, and increased pH, but lower P and B concentrations were found in the street soils in comparison to the park soil. Significantly higher concentrations of Na, Cl, and Mg, and lower concentrations of K, Fe, Cu, and B, as well as unfavourable ratios of several element concentrations were found in the soils where more damaged street trees were growing. In addition, the recommended fertilization regimes are discussed.