Performance of geophytes on extensive green roofs in the United Kingdom

Dwarf geophytes have great potential for use on extensive green roofs because they often come from arid areas and can survive dry and hot summer in a dormant state. However, there has been little research regarding geophytes on green roofs. This experiment was conducted to study the performance of 26 species of geophytes on a green roof during 2005–2006 in Sheffield, UK. The geophytes were grown at two substrate depths (5 cm and 10 cm) of substrate on a green roof without irrigation. To investigate the susceptibility of geophytes to competition from a covering of permanent plants, the geophytes were grown with or without a surface vegetation layer of Sedum album. Overall, the growth, survival rate, regeneration and flowering of geophytes were more successful at a substrate depth of 10 cm than of 5 cm, probably because of improved moisture retention, fewer temperature fluctuations and the protection from digging by animals. The flowering period was limited to spring, therefore, it is recommended to combine with other plant species such as covering plants. Geophyte species did not compete much with S. album and Sedum cover had no significant effects on the growth, survival rate, regeneration and flowering of geophytes in most species. Iris bucharica, Muscari azureum, Tulipa clusiana var. chrysantha, Tulipa humilis, Tulipa tarda and Tulipa turkestanica had good performance at the substrate depth of 5 cm. In addition, Narcissus cyclamineus ‘February gold’ and Tulipa urumiensis exhibited a successful performance at the substrate depth of 10 cm.     

Responses of native Lupinus varius (L.) to culture conditions: effects of photoperiod and sowing time on growth and flowering characteristics

The effects of photoperiod and sowing time on growth and flowering characteristics of Lupinus varius were investigated during two growing periods to determine its responses to culture conditions as a potential native cut-flower crop. The seeds were sown in an unheated plastic greenhouse on 28 September, 28 October and 28 November under natural, 14- and 16-h day-length treatments. 14- and 16-h day-lengths were established by lengthening the natural day-lengths to 14 and 16 h with the use of night break photoperiodic lighting at 1.8–1.9 μmol m⁻² s⁻¹ in 400–700 nm. Photoperiodic lighting, in particular the 16-h day-length treatments, slightly (maximally 15 days) shortened days to flowering and increased plant height in all sowing times relative to natural photoperiods. There were no significant differences in stem and branch inflorescence diameters, in lengths of branch, in main and branch inflorescences in plants grown under natural photoperiod, and 16-h day-length treatments. The highest main inflorescence diameter, the number of branches per plant, and flower numbers on main and branch inflorescences were recorded in plants grown under natural photoperiods, whereas 14-h day-length treatments did not provide sufficient specimens to allow for the measurement of most of the characteristics studied. These findings were interpreted to indicate that L. varius behaves as a facultative long day plant. Additionally, there was a particular shortening of days to flower and growth, and flowering quality decreased linearly with delayed sowing dates under all photoperiodic treatments. The earliest and latest flowering dates were recorded for plants sown in September under 16-h day-length, and plants sown in November under natural photoperiods, respectively. Therefore, sowing in September under natural photoperiods or 16-h artificial day-length resulted in earlier flowering dates and a longer time from sowing to flowering and was consequently the best sowing time with respect to all of the characteristics considered in this study.     

Environmental factors affecting flowering of rice flower (Ozothamnus diosmifolius,Vent.)

Rice flower (Ozothamnus diosmifolius, Vent.), native to east Australia, is a spring flowering perennial shrub. It is a new cut flower plant, recently introduced into cultivation in Australia and in Israel. Its response to environmental conditions, which affect growth and flowering, are not yet known. The purpose of the present study was to evaluate the effects of growth temperature, photoperiod and total solar energy on flowering. Experiments were conducted with plants of the cv. Cook’s Snow White. Plants were grown in three cycles under controlled conditions in the phytotron, at four day/night temperature regimes: 17/9, 20/12, 23/15 and 26/18°C. Two photoperiods — short day (SD) of 10 h natural day light and long day (LD) of 10 h natural light plus 10 h incandescent light — were employed. High temperatures enhanced vegetative growth but blocked flowering under both LD and SD. Under medium–moderate temperatures plants were absolute LD plants and did not flower under SD conditions. Under lower temperatures plants flowered under both LD and SD, but SD delayed flowering. High total solar radiation under LD did not affect flowering time but greatly promoted the number of flowering stems.     

Performance of herbaceous Evolvulus pilosus on urban green roof in relation to substrate and irrigation

Rooftop gardening (or green roof establishment) is an urban greening afforestation method that has many environmental, economic, and urban landscaping benefits. For rooftop vegetation, stressful environments that include heat, strong winds, sunshine, and drought prevent many plants from growing well, especially in shallow soil. To establish low cost urban rooftop gardens with a low weight substrate in the summer, we evaluated the green coverage and growth of a suitable groundcover ornamental plant, blue daze (Evolvulus pilosus). Blue daze was used as rooftop vegetation in a shallow substrate (10 cm thick) on the flat rooftop of a four-story building in the middle of Kobe city, Japan, which has a temperate and humid climate. On average, the diurnal maximum temperatures and the total amounts of precipitation during each planting experiment between July and September were 30.8 °C and 247 mm in 2008 and 33.2 °C and 458 mm in 2009, respectively. Three different types of planting substrates (AS, amended soil, TM, turf mat as a dried-up blocks of sod, and FBA, furnace bottom ash) were tested to determine how they influenced plant cover, flowering, and growth. We evaluated the physical and chemical properties of the substrates that were used to establish the rooftop greeneries. In addition, the economy, ornamental and ecological values, reuse of material, and low rooftop weight burdens of the substrates were evaluated. The greatest blue daze ground cover occurred on the TM substrate (relative to the AS and FBA substrates) approximately three months after transplanting. The blue daze actively bloomed on all substrates throughout midsummer. However, alternate day irrigation largely reduced their shoot growth and flowering relative to daily irrigation. The AS and TM substrates had suitable physicochemical properties for use as planting substrates and had ideal solid, liquid, and vapor phase distributions and high water and nutrient holding capacities. FBA was a poor substrate with very low water and nutrient retention capacities, which resulted in depressed plant growth, especially under low watering conditions. To recycle FBA efficiently as a shallow low-cost planting substrate for rooftop gardening, the addition of coated fertilizers and organic matter to FBA should be considered to improve its water and nutrient holding capacities.     

Temperature effects on corm dormancy and growth of Zephyra elegans D.Don

Experiments were performed with the Chilean geophyte Zephyra elegans, a potential cut flower, to evaluate the effect of corm weight and storage temperature on corm dormancy, and to determine the effect of day and night growing temperatures on its growth and flowering. Z. elegans has a deciduous and synanthous growth habit and the corm is replaced annually. Dormant corms were stored at different constant temperatures or temperature combinations from 20 to 40 °C. Corms released from their dormancy were grown at 15/10, 20/15, or 25/20 °C day/night temperatures. Corms of various weights were planted at the same date after being stored dry at 25 °C for 22 weeks. They all emerged 19–38 days after planting, showing that dormancy release was not affected by corm weight. A 20-week corm storage treatment at a constant 25 °C resulted in the most rapid corm sprouting. Sprouting percentage was reduced at higher or lower storage temperatures. Temperature also affected plant growth. When plants were grown at 15/10 or 20/15 °C they emerged and flowered more rapidly than when they were grown at 25/20 °C. The latter growing temperature also resulted in poor flower quality.     

An evaluation of one example of biotope roof in Japan: Plant development and invertebrate colonisation after 8 years

Biotope roofs in Japan are usually intensive green roofs that primarily include native plants and food plants for invertebrates and a pond and stones to create a wide range of habitats. The study aimed to evaluate the survivability of planted species, and colonisation by plants and invertebrates on a biotope roof and to suggest an appropriate planting design and maintenance scheme to optimize biodiversity benefits. An intensive green roof (150 m², substrate depth of 50 cm) was installed in 2002 on the ninth storey of a building at Chiba University, Japan. Twelve species of trees, 18 species of shrubs and 8 species of forbs (mainly native species) were planted and volcanic stones were used as mulch and to create habitats for invertebrates. No maintenance and no irrigation were applied for almost 8 years. A limited number of tree species, such as Myrica rubra and Cinnamomum camphora could grew well without maintenance and irrigation at a substrate depth of 50 cm. Overall, shrubs grew successfully and a high density planting seemed effective in increasing wind resistance. Most forbs disappeared, probably because of drought and competition with these colonising plants. Eleven plant species spontaneously colonised resulting in domination by Solidago altissima and Miscanthus sinensis. These two species were too aggressive, and selective weeding is required for species richness. In an invertebrate study, 46 species in 11 orders were observed and the highest number of invertebrate species was observed in the pond and shady areas.     

Positive effect of salicylates on the flowering of African violet

Aqueous solutions of 1.0 μM to 0.1 nM concentrations of salicylic acid (SA) were sprayed on African violet grown under greenhouse conditions to estimate its effect on the flower expression of the plant. These solutions were sprayed on the shoots of the plant on three occasions, 21, 28 and 35 days after being potted. Salicyliclate at 0.1 nM increased the number of leaves from 16 to 19, the number of flower primordia from 8 to 14, the rosette diameter from 130 to 177 mm in comparison with the control. The same concentration induce flowering at 74 days of plant age whilest the control plants last 89 days to flower.     

Flowering of Primula malacoides in response to photoperiod and temperature

Primula malacoides Franch. ‘Prima Lilac’ was grown at 16 or 20 °C in combination with short days (SD, 8 h) or long days (LD, 16 h). In addition to uninterrupted growing conditions, plants within each temperature were moved at weekly intervals to the other photoperiod and left until termination. Temperature, but not photoperiod, significantly affected the rate of development from start of treatments (51 days from seeding) to 2 mm visible flower bud (VB). At 16 °C, VB averaged 30 days and at 20 °C, 48 days. Time to flower (first horizontal petals) at 16 °C increased from 56 to 64 days as SD increased from 1 week to continuous conditions while LD decreased time to flower from 64 to 56 days. Time to flower at 20 °C varied from 73 to 87 days with additional SD exposure resulting in slower and LD in faster flowering. These observations of the flowering response in ‘Prima’ are contrary to the photoperiodic classification of P. malacoides as a SD plant.     

Plant establishment on a green roof under extreme hot and dry conditions: The importance of leaf succulence in plant selection

Plant selection for extensive green roofs has largely been based on cool, temperate climate research. However, as green roof implementation in hotter and drier climates increases, there is a need to evaluate plant performance under these climatic conditions. Succulents have been shown to be successful in hot and dry green roofs, although survival differs between species and the role of leaf succulence in survival has not been fully explored. For non-succulent plants, habitats with conditions similar to green roofs (‘habitat templates’) have been used to select plants, although few studies have discussed the performance of these selections under green roof conditions. Therefore, we evaluated establishment of 32 plant species on an unirrigated extensive (125 mm deep) green roof in Melbourne, Australia over a 42 week period (from winter through summer into autumn). Plants were selected on the basis of life-form, succulence, appropriate habitat templates and/or successful use on green roofs internationally. Climatic conditions during the experiment were often extreme, with evaporation regularly exceeding rainfall and a hot and dry summer (mean maximum air temperature 35 °C and 80.6 mm total rainfall), leading to roof temperatures of 65 °C. After 42 weeks, only succulent plants remained alive and only three of the succulent species had 100% survival. Survival was positively related to the degree of leaf succulence (g H₂O leaf area cm⁻¹) making this a useful trait for plant selection for unirrigated green roofs in hot, dry climates. The failure of most species, despite being chosen from appropriate habitats, demonstrates the need to evaluate potential plants on green roofs under extreme climatic conditions. Supplementary irrigation may be essential to sustain non-succulent species during extreme weather in hot and dry climates.     

Diversity and ecology of vascular plants established on the extant world-longest ancient city wall of Nanjing,China

Spontaneous vegetation established on the city wall constitutes a characteristic greenspace within the urban matrix. Nanjing city wall of the Ming Dynasty (NJCW), as an extraordinary huge defensive masonry project, was built in 1393, the extant, basically intact ancient city wall is 25.09 km long, 9–26 m high, and is protected now as a key national cultural relic. Species composition and life forms of the vascular plants established on the vertical or inclined wall surfaces of NJCW were investigated, and its diaspore sources and dispersal modes were also analyzed. Totally, 159 species in 125 genera of 70 families were found inhabiting the joints between bricks or between block stones, trees, shrubs and woody lianas accounts for 51.57% of the species assemblage, while herbaceous plant species makes up 48.43% of them. Fifteen alien species were found colonizing NJCW, including 12 invasive species. Six 100-m-long quadrats were sampled in different segments of NJCW, each quadrat contained 39–77 species, and 755–3006 individuals. In total, 10785 individuals of vascular plants were recorded, consisting of 104 species in 89 genera of 56 families. 65.25% of the total individuals, and 53.85% of the total species are adapted to the primary dispersal of diaspores by wind, whereas 34.75% of the individual assemblage, and 46.15% of the species assemblage are adapted to the primary dispersal of seeds by birds. A bird-dispersed, native pioneer tree, Broussonetia papyrifera, was the most abundant species among the six quadrats, even developed coppices on the vertical wall surface. Location and aspect of the quadrats may have affected the species diversity of vascular plants established on its wall surfaces. A diversity of vascular plants established on NJCW, as a valuable urban ecological heritage, is worthy of sustainable wall management, while management priorities should be given to those large trees inhabiting the walls made of bricks, and to the invasive alien species to prevent them from further spreading over the adjacent urban habitats.     

The impact of photoperiod and irradiance on flowering of several herbaceous ornamentals

Forty-one herbaceous species were grown under short-days (8 h photoperiod, ambient irradiance averaged 12–13.2 and 6.4–8.3 mol m⁻² day⁻¹ for Experiments I and II, respectively) with or without supplemental high-pressure sodium lighting (+50, 100, or 150 μmol m⁻² s⁻¹); or under long-days delivered using natural day lengths and irradiance with night interruption lighting (2200–0200 h at 2 μmol m⁻² s⁻¹ from incandescent lamps) or under ambient daylight plus supplemental irradiance during the day and as a day extension to 18 h (0800–0200 h) with supplemental high pressure sodium lighting (+50, 100, or 150 μmol m⁻² s⁻¹) to identify the impact of photoperiod and irradiance on flowering of each species. Days to first open flower, leaf number below first flower, and mean dry weight gain per day (MDWG) were measured when the first flower opened. Twenty-seven species were photoperiodic with examples of five photoperiodic response groups represented: obligate short-day (2), facultative short-day (5), obligate long-day (16), facultative long-day (4); 13 were day neutral (no photoperiod response in flowering). One species, Salvia sclarea L., did not flower. A facultative irradiance response was observed with 10 species; 28 species were irradiance indifferent; 2 had delayed flowering as irradiance increased. Photoperiod affected MDWG of 30 species. Increasing irradiance affected MDWG with 14 species. Photoperiod interacted with irradiance to affect MDWG of 11 species. Cobaea scandens had the greatest MDWG (0.40 g day⁻¹) while Amaranthus hybridus had the least MDWG (0.01 g day⁻¹) across photoperiod and irradiance levels.     

Shoot induction and plant regeneration from receptacle tissues of Lilium longiflorum

An efficient system has been developed for the in vitro plant regeneration of Lilium longiflorum Thunb. by culturing receptacle sections from flower buds. The sections were cultured on one-half MS medium plus 30 g l⁻¹ sucrose, 8 g l⁻¹ agar, 5.4 μM NAA or 4.9 μM IBA plus 2.2 μM BAP. A section size of 3–4 mm was found to be optimal. After 60 days an average of 41 shoots were formed per explant. More vigorous shoots were obtained by subculturing on hormone-free medium with 20 g l⁻¹ sucrose. Rooting occurred on one-half MS medium with 1.1 μM NAA. Rooted plants were hardened-off in a greenhouse for two months, and normal flowering plants were produced.     

Effect of photoperiod and light integral on flowering and growth of Eustoma grandiflorum (Raf.) Shinn.

The aim of the study was to examine the effects of different photoperiod and light integral on floral initiation, development and subsequent growth of Eustoma grandiflorum (Raf.) Shinn. Six-weeks-old seedlings of ‘Echo Blue’ and ‘Fuji Deep Blue’ were placed under short day (SD, 10 h) and were transferred to long days (LD, 20 h) at 2-week intervals from 6 to 14 weeks after seeding. Plants initiated flower buds regardless of light regimes. Flower bud initiation was delayed by SD compared to LD; plants transferred after 6 weeks from seeding initiated flower buds at least 21 and 10 days earlier at LD at high (HL) and low (LL) daily light integral, respectively, compared to those at SD. Light regimes had little or no effect on time to flower bud development after initiation. Thus, it seems likely that LD and HL affected the initiation rather than development. Both the photoperiod and light integral strongly influenced the subsequent growth after initiation. SD delayed the time to visible bud (VB), increased the number of nodes to first open flower, number of branches, stem diameter and shoot dry weight compared to LD. HL promoted flowering and increased several shoot characteristics and flowering compared to LL.The results indicate that Eustoma is a quantitative long-day plant. LD, and more specifically HL, enhanced flower bud initiation, development and subsequent growth. An initial SD period is preferred to increase the number of branches, number of flowering buds and flowers, stem diameter and shoot dry weight.     

Effect of photoperiod on flower bud initiation and development in myoga (Zingiber mioga Roscoe)

Selection of suitable production locations in Australia and New Zealand for production of myoga (Zingiber mioga Roscoe) has been limited by lack of information on climatic influences on flowering. This study focused on photoperiod as potential production sites within Australia differ considerably in daylength due to the geographical range. The two cultivars available in Australia (Inferior and Superior) were examined in this trial due to previously observed differences in vegetative and reproductive development.Plants grown under long-day conditions (16 h) and short-day conditions (8 h) with a night break produced flower buds, while those under short-day conditions (8 h) did not. The failure of plants under short-day conditions to produce flower buds was due to abortion of developing floral primordia rather than a failure to initiate inflorescences. It was concluded that for flower development in myoga a qualitative long-day requirement must be satisfied, but that flower initiation was day-neutral.Short-day conditions resulted in abortion of flower primordia, premature senescence of foliage and reduced foliage dry weight in both cultivars. Early senescence and low flower bud yield of the Inferior cultivar, but not the Superior cultivar have been observed in crop evaluation trials in Southern Australia and New Zealand. Differences in critical photoperiod between the two cultivars may explain this observation and therefore photoperiodic requirements may be an important consideration in site and planting date selection for different cultivars.     

An adaptive approach to intensive green roofs in the Mediterranean climatic region

The present study aims to introduce an adaptive approach to intensive green roofs by evaluating suitable, lightweight substrates and by determining the effect of their depth on the growth and physiological status of Pittosporum tobira L. and Olea europaea L. The two-year study was conducted in outdoor containers (1.2 m × 1.2 m) while treatments included the use of two depths (30 cm and 40 cm) and three different substrates: (a) pumice (Pum) mixed with peat (P) and zeolite (Z) in a volumetric proportion of 65:30:5 (Pum₆₅:P₃₀:Z₅), (b) pumice mixed with compost (C) and zeolite in a volumetric proportion of 65:30:5 (Pum₆₅:C₃₀:Z₅) and (c) sandy loam soil (S) mixed with perlite (Per) and zeolite in a volumetric proportion of 30:65:5 (S₃₀:Per₆₅:Z₅). Each experimental plot was planted with four plants of P. tobira and one plant of O. europaea var. Koroneiki. Measurements included determination of the physical and chemical characteristics of the substrates while plant growth and physiological status were determined through plant growth index, trunk perimeter for olive trees, SPAD measurements and chlorophyll_a+b content. Both the plant species exhibited better growth and higher chlorophyll content in the compost-amended substrate (Pum₆₅:C₃₀:Z₅) due to its higher nutrient content. The 40 cm depth substrate provided minimal improvement in the growth of both the plants at the end of the first year while in the second year the deeper substrate positively influenced the growth of olive trees.     

Weather effect on thermal and energy performance of an extensive tropical green roof

This study investigated the weather effect on thermal performance of a retrofitted extensive green roof on a railway station in humid-subtropical Hong Kong. Absolute and relative (reduction magnitude) ambient and surface temperatures recorded for two years were compared amongst antecedent bare roof, green roof, and control bare roof. The impacts of solar radiation, relative humidity, soil moisture and wind speed were explored. The holistic green-roof effect reduced daily maximum tile surface temperature by 5.2 °C and air temperature at 10 cm height by 0.7 °C, with no significant effect at 160 cm. Green-roof passive cooling was enhanced by high solar radiation and low relative humidity typical of sunny summer days. High soil moisture supplemented by irrigation lowered air and vegetation surface temperature, and dampened diurnal temperature fluctuations. High wind speed increased evapotranspiration cooling of green roof, but concurrently cooled bare roof. Heat flux through green roof was also weather-dependent, with less heat gain and more heat loss on sunny days, but notable decline in both attributes on cloudy days. On rainy days, green roof assumed the energy conservation role with slight increase instead of reduction in cooling load. Daily cooling load was 0.9 kWh m^?2 and 0.57 kWh m^?2, respectively for sunny and cloudy summer days, with negligible effect on rainy days. The 484 m² green roof brought potential air-conditioning energy saving of 2.80 × 10⁴ kWh each summer, equivalent to electricity tariff saving of HK$2.56 × 10⁴ and upstream avoidance of CO₂ emission of 27.02 t at the power plant. The long-term environmental and energy benefits could justify the cost of green roof installation on public buildings.     

Day and night temperatures,daily light integral,and CO2 enrichment affect growth and flower development of Campanula carpatica ‘Blue Clips’

Campanula carpatica Jacq. ‘Blue Clips’ plants were grown in a greenhouse under nine combinations of day and night temperatures created by moving plants every 12 h among three day/night temperatures (15, 20, and 25°C). At each temperature, there were three daily light integrals (DLI; 4.2, 10.8, and 15.8 mol m⁻² per day, averaged over the experimental period) created with varying supplemental light, and ambient (≈400 μmol mol⁻¹) and enriched (≈600 μmol mol⁻¹) CO₂ concentrations. Time to flower was closely related to average daily temperature (ADT), and was not significantly affected by the day or night temperatures delivered to achieve a specific ADT. Time to flower was not largely affected by DLI or CO₂ enrichment. As plant ADT increased between 15 and 25°C, flower diameter decreased about 1 mm per degree and was not related to the difference between day and night temperatures (DIF). Flower diameter was smallest and least sensitive to changes in temperature at lower DLI and at ambient CO₂ levels. There were 10 less flower buds and 0.3 g less dry mass per plant at first flower for every 1° increase in plant ADT at high and medium DLIs. Flower bud number and dry mass were relatively low and less sensitive to changes in ADT at low DLI, and increased slightly with CO₂ enrichment at medium and high but not at low DLI. Plant height was not related to ADT, but increased linearly as DIF increased from −6 to 12°C at all DLIs, but the response was stronger under low DLI than high and medium DLIs. Flower bud number and dry mass were correlated closely with the ratio of DLI to daily thermal time (base temperature of 0°C). Flower bud number and dry mass were highest when C. carpatica plants were grown at 15°C with a DLI of 10–15 mol m⁻² per day.     

Quality assessment of three warm-season turfgrasses growing in different substrate depths on shallow green roof systems

In an effort to increase the accessibility and functionality of shallow green roof systems, the ability of warm-season grasses to provide acceptable growth needs to be further investigated. In the current study, which was conducted during 2011 and 2012, three warm-season grasses (hybrid bermudagrass, Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy ‘MiniVerde’; seashore paspalum, Paspalum vaginatum Swartz ‘Platinum TE’ and zoysiagrass, Zoysia japonica Steud. ‘Zenith’) were established in outdoor lysimeters. The lysimeters were equipped with all necessary green roof layers placed below a coarse-textured substrate that comprised pumice, thermally treated attapulgite clay, peat, compost and zeolite. Half of the lysimeters had a substrate depth of 15 cm, while the other half had a substrate depth of 7.5 cm. Irrigation was applied at crop evapotranspiration (ET_c). Measurements included determination of substrate moisture content, green turf cover (GTC) and leaf stomatal resistance. Significant differences were observed in the values of GTC among the three turfgrass species and the two substrate depths. Zoysiagrass exhibited the best adaptation at the lower depths of shallow green roof systems. At 15 cm substrate depth, zoysiagrass managed to sustain green coverage for the two study periods. In addition, it was the only turfgrass species that managed to perform well at the substrate depth of 7.5 cm. Seashore paspalum exhibited limited green cover at both substrate depths, while hybrid bermudagrass could provide acceptable green coverage only at 15 cm substrate depth.     

Enhancing plant diversity and mitigating BVOC emissions of urban green spaces through the introduction of ornamental tree species

Promoting the plant diversity of urban green spaces is crucial to increase ecosystem services in urban areas. While introducing ornamental plants can enhance the biodiversity of green spaces it risks environmental impacts such as increasing emissions of biogenic volatile organic compounds (BVOCs) that are harmful to air quality and human health. The present study, taking Qingdao City as a case study, evaluated the plant diversity and BVOC emissions of urban green spaces and tried to find out a solution to increase biodiversity while reducing BVOC emissions. Results showed that: (1) the species diversity and phylogenetic diversity of trees in urban green spaces were 22% and 16% lower than rural forest of this region; (2) urban areas had higher BVOC emission intensity (2.6 g C m⁻² yr⁻¹) than their rural surroundings (2.1 g C m⁻² yr⁻¹); (3) introducing the selected 11 tree species will increase 15% and 11% of species diversity and phylogenetic diversity, respectively; and (4) the BVOC emissions from green spaces will more than triple by 2050, but a moderate introduction of the selected low-emitting trees species could reduce 34% of these emissions. The scheme of introducing low-emitting ornamental species leads to a win–win situation and also has implications for the sustainable green space management of other cities.     

Prohexadione-calcium affects growth and flowering of petunia and impatiens grown under photoselective films

The response of petunia (Petunia x hybrida Vilm.-Andr. ‘Countdown Burgundy’) and impatiens (Impatiens wallerana Hook ‘Accent Orange Tempo’) to Prohexadione-calcium was evaluated under a clear and a far-red light absorbing greenhouse (A_FR) film to investigate the dosage effect of Prohexadione-Ca and to determine if it can overcome the flowering delay under FR deficient greenhouse environments. Prohexadione-Ca reduced stem elongation of petunia and impatiens under A_FR and clear films when applied 3 weeks after germination. Late applications were less effective. In both crops, main stem length decreased in a quadratic pattern as the concentration of Prohexadione-Ca increased. Under both films, 50–100 mg l⁻¹ Prohexadione-Ca resulted in ≈30% shorter petunia plants. Greater concentrations (500 and 1000 mg l⁻¹) resulted in excessively short plants (over 70%). Prohexadione-Ca at 100 mg l⁻¹ delayed anthesis of petunia by 8 and 3 days under the clear film and the A_FR film, respectively during less inductive photoperiods but had no effect during inductive photoperiods. In impatiens, Prohexadione-Ca at 100 mg l⁻¹ delayed anthesis over 10 days under clear or A_FR film. Greater concentrations (200 and 300 mg l⁻¹) inhibited flowering of impatiens. Prohexadione-Ca treatments significantly affected flower color development. Untreated petunia plants had dark burgundy flowers. Prohexadione-Ca treatment increased L*, a*, and C* values and decreased hue angle indicating that the flowers were faded. Flowers of untreated impatiens plants were bright orange color. Prohexadione-Ca at 100 mg l⁻¹ increased L* value and decreased a*, b*, and C* values indicating that significant petal fading had occurred. Flowers of treated plants were nearly white under both films. Although effective in height control, loss of color would be a major limitation to the use of Prohexadione-Ca on flowering crops.