Bauhinia Blakeana Research Articles

Using roof garden to alleviate urbanization problems -- A case study of Chengdu city

The accelerated process of urbanization has led to significant urbanization issues such as noise pollution, air pollution, and the urban heat island effect. Roof gardens, as an effective way to create green spaces within cities, have considerable potential to address these urbanization problems. Taking Chengdu City as an example, this paper presents a simple design for a roof garden, focusing on the infrastructure, layout, plant species, and materials of the roof garden. The roof garden was improved after establishing its potential to mitigate urban noise by initial qualitative analysis. Firstly, specific vegetation selections are made which include deciduous trees such as Cephalotaxus Harrington and shrubs like Bauhinia blakeana. which can adapt to Chengdu's climate while effectively capturing dust particles. Secondly, a water storage layer was installed, and the angle of the pavilion roof was adjusted which allows the roof garden to regulate rainwater runoff effectively and minimize potential problems as possible. Although the current roof garden design is still in the theoretical stage and requires further field research and design, it holds tremendous potential in dealing with urban issues due to its unique advantages and policy support.

Phytochemical Screening, Antioxidant Activity and α‐Glucosidase Inhibitability of Bauhinia  blakeana Dunn Leaf and Flower Extracts from Vietnam

Bauhinia  blakeana Dunn is traditionally used as vegetables, medicinal herbs to treat diseases, and ornamental trees. The current study was performed to evaluate the phytochemicals, total phenolic (TPC) and total flavonoid (TFC) contents, antioxidant activity, and α‐glucosidase inhibitability of Bblakeana leaf and flower from Vietnam. Qualitative phytochemical analysis showed positive results for carbohydrates, organic acids, carotenoids, steroids, cardiac glycosides, triterpenoids, saponins, flavonoids, and tannins. The TPC and TFC obtained from B blakeana leaf were 99.81 ± 0.94 (mg GAE/g E) and 114.93 ± 1.06 (mg RE/g E), respectively, whereas they were 40.45 ± 0.50 (mg GAE/g E) and 59.61 ± 0.85 (mg RE/g E) from B blakeana The DPPH radical scavenging capacity assay of the crude ethanolic extracts of B blakeana leaf (IC50 = 266.52 ± 1.03 μg/mL; R2 = 0.9864) and flower (IC50 > 1000 μg/mL) was determined. The leaf and flower extracts showed significant α-glucosidase inhibitory activity with IC50 values of 61.88 ± 0.19 μg/mL (R2 = 0.9838), 190.79 ± 0.18μg/mL (R2 = 0.9891), respectively. These results indicated that the extract of B blakeana leaf and flower can be a promising candidate for alternative drug or functional food discovery, and nutritional recommendations for the control of oxidative stress and diabetes.

First Report of Colletotrichum endophyticum, a Causal Agent of Leaf Spot of Bauhinia blakeana in Southwest China.

The Bauhinia blakeana is originated in South Asia and is widely planted in Chinese cities. It is distributed in Guangdong, Fujian, Hainan, Guangxi, Sichuan, and other places in China (Gu S et al. 2019). It is applied to urban greening as the street trees, garden trees, and scenic forest trees, and is an excellent landscaping tree species in South China. In August 2021, the new leaf spot disease was found in Chengdu (30°42'N, 103°51'E), and the incidence rate was about 70%. The symptoms began to appear from April to May, the worst from June to August. Firstly, the typical symptom is that round, oval, or irregular, brown and slightly concave necrotic spots begin to appear at the edge of the leaves, and the color of the spots changes from light brown to dark brown. Gradually, the number of necrotic spots increases and the spots spread from the edge of the leaf to the middle of the leaf. There is an obvious dark brown boundary between the diseased part and the healthy part, and their yellow-green halos around the spots. Finally, the leaves turn yellow and fall off. On September 1, 2021, infected tissue from samples was cut into small pieces 5 × 5 mm, surface sterilized for 30 seconds in 3% NaClO, 60seconds in 75% ethanol, rinsed three times in sterile water, placed on potato dextrose agar (PDA) amended with streptomycin sulfate (50 μg/mL), and incubated at 25°C in a dark. Finally, 10 typical isolates exhibited the morphology described as Colletotrichum endophyticum (De Silva et al. 2019). After 6 days, the colony diameter reached 63.4 to 67.7mm and had white to pale orange aerial mycelium, but was grey-green at the base. Black conidia formed after 10 days, which were round, oval, elongated spindle-shaped, with sharp ends, measuring 3.25 to 5.85 x 1.95 to 2.60μm (average: 6.18 x 2.28μm). Since the 10 isolated strains were consistent in morphology, a representative strain was selected from the 10 isolated strains to continue the next test. For molecular identification, DNA was extracted from 10 fungal colonies (the 10 fungal colonies used to isolate genomic DNA were derived from single isolates) using a plant genomic DNA extraction kit (Solarbio, Beijing). The 5.8S nuclear ribosomal genes with the two flanking internal transcribed spacer (ITS), the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), partial sequences of the actin (ACT) and beta-tubulin (TUB2) genes were amplified and sequenced using the primer pairs ITS4/ITS5 (White et al. 1990), ACT-512F/ACT-783R (Carbone and Kohn. 1999), GDF1/GDR1 (Guerber et al. 2003) and T1/Btub4R (O'Donnell and Cigelink. 1997; Aveskamp et al. 2009), respectively (Fang Qiu et al. 2021). Sequences were deposited in GenBank (ITS:OK560626; ACT:OK562583; GAPDH:OK562584; TUB2:OK562585). BLAST analysis showed >98% identity with several reference sequences of C. endophyticum previously deposited in GenBank. To confirm pathogenicity and fulfill Koch's postulates, the pathogenic fungal cakes were inoculated on the leaves of 5-year-old B. blakeana, and the sterile medium was used as a control. Three fungal cakes were placed on each leaf and repeated three times. Five days later, the inoculated plants showed the similar symptoms observed in diseased plants; controls remained asymptomatic. The C. endophyticum was re-isolated from the infected leaves and identified by morphological characteristics and DNA sequence analysis. The pathogenicity test was repeated three times with similar results, confirming Koch's postulates. This is the first report of B. blakeana leaf spot caused by C. endophyticum in China.

Study of Phenotypic Variability of Kachnar (Bauhinia spp.)

An investigation to Study of phenotypic variability of Kachnar (Bauhinia spp.) was conducted in the Department of Floriculture and Landscape Architecture, IGKV Raipur, Chhattisgarh, during the Rabi season of 2021–2022. Five species for the study were Bauhinia purpurea, Bauhinia acuminata, Bauhinia blakeana, Bauhinia tomentosa and Bauhinia variegata. Different growth characteristics including plant, leaf, flower, and fruit traits, were recorded. According to the findings, Bauhinia purpurea had the tallest plants followed by Bauhinia blakeana, Bauhinia variegata, Bauhinia acuminata, and Bauhinia tomentosa. The longest and widest leaf was measured in Bauhinia purpurea 14.91and 12.04 respectively. Smallest and narrowest leaf was recorded in Bauhinia tomentosa 4.71 and 4.20 respectively. Among all the five species of Bauhinias highly pubescent leaf was discovered in Bauhinia tomentosa only. The Bauhinia acuminata's 3.96 long petiole had the record for being the longest while the Bauhinia tomentosa's 2.10 petiole had the smallest. The Bauhinia blakeana flower measuring 13.160.07 cm had the largest flowerdiameter while Bauhinia tomentosa 3.91 0.41 cm was the smallest. The only Bauhinia species with a pubescent flower bud was Bauhinia tomentosa. Longest petal, stamen and pistil length recorded in Bauhinia blakeana measuring 7.09, 4.8 and 6.91 respectively. Maximum pod length measuring 29.33 and maximum number of seeds per pod 11.90 was recorded in Bauhinia purpurea and minimum pod length measuring 9.25 in Bauhinia acuminata. Minimum number of seeds per pod recorded in Bauhinia acuminata. Bauhinia blakeana did not produce any pods as these species were infertile. The maximum seed weight was recorded in Bauhinia purpurea 30±0.87g and minimum in Bauhinia tomentosa 3.35±0.44g.

Experimental and theoretical study of urban tree instantaneous and hourly transpiration rates and their cooling effect in hot and humid area

The transpiration of trees is an important factor in the surface energy balance and the hydrosphere-atmosphere-biosphere water vapor cycle. It is also the main cause of a tree’s ecological effects, such as cooling and humidification. A major challenge is to establish a model that can accurately predict the transpiration rate of urban trees at different time scales. To address this challenge, field measurements are used to obtain the instantaneous and hourly transpiration rates of four common subtropical trees (Bauhinia blakeana, Mangifera indica, Ficus microcarpa and Michelia alba), and their cooling effects are analyzed. The transpiration rate for the four trees ranges from 18 to 54 mg m−2 s−1, and the estimated energy loss due to transpiration ranges from 178 to 274 W/m2, with an average of 229 W/m2. On average, 33.2 % of incoming solar radiation is converted into latent heat. The Shuttleworth-Wallace model, including canopy resistance and soil resistance parameters, is adapted to urban tree characteristics in built-up environments. The resulting model is a theoretical model that provides a new methodology and reasonable results for predicting an urban tree’s transpiration rate under urban conditions. Its accuracy at different time scales is verified with field measurements. The predictability of water vapor cycle, thermal comfort and surface energy budgets in urban environments will be enhanced by incorporating the transpiration model into urban canopy model. Future applications and development of this model will help provide guidelines for sustainable urban planning and urban landscape management in terms of water vapor cycle and heat island mitigation.

A green tactic for inhibition of corrosion on mild steel in bore well water by aqueous extract of Bauhinia Blakeana leaves

The impact of an aqueous extract of Bauhinia Blakeana leaves (AEBBL) in controlling the corrosion of mild steel in bore well water medium has been demonstrated by mass loss method and electrochemical measurements. The extract is characterized by Fourier-Transform Infrared Spectroscopy (FTIR) and the active ingredients present in the AEBBL are identified by Gas Chromatography-Mass Spectrometry (GC-MS). The surface morphology is examined with the help of Scanning electron microscopy (SEM) and the surface roughness analysis is done by Atomic force microscopy (AFM). Weight loss method reveals that of the extract offers a maximum corrosion inhibition efficiency of 96.62 . Potentiodynamic polarization study (PDP) and Electrochemical impedance spectroscopy (EIS) are used to study the mechanistic aspects of corrosion inhibition. Both the double layer capacitance (Cdl) and corrosion current (Icorr) values decreases while the charge transfer resistance (Rct) value increases with the increase in concentration of AEBBL. The potentiodynamic polarisation reveal that AEBBL acts as mixed type inhibitor with primarily cathodic effectiveness. SEM and AFM documented the development of shielding coating on the mild steel surface.

Loss and recovery of leaf hydraulic conductance: Root pressure, embolism, and extra-xylary resistance

Vascular networks in plant leaves must provide for the safe and efficient transport of water, nutrients, and energy; however, the conditions whereby these networks lose and regain conductive capacity are still poorly understood. We measured the loss and recovery of leaf hydraulic conductance (Kleaf) in a tropical monocotyledon (Bambusa vulgaris) and dicotyledon species (Bauhinia blakeana) using Rehydration Kinetics Method (RKM) as well as a recently developed optical method. We found that both species lost ca 88% of their maximal Kleaf (measured by RKM) before any embolization was detected in their conductive elements (via optical observation). This suggests that the majority of loss in Kleaf, as measured with RKM, was associated with resistances other than embolization. Furthermore, embolism in B. vulgaris, a species known to generate root pressure, was reversed when rehydrated under positive pressure (120 kPa), but not under atmospheric pressure. In contrast, embolism was not reversed in B. blakeana under either elevated or atmospheric pressure. However, reductions in Kleaf that was not associated with embolization was recovered by this species when rehydrated under atmospheric conditions, whereas B. vulgaris did not exhibit any recovery under the same conditions. We suggest that root pressure is an adaptive mechanism allowing for the reversal of embolism and the recovery of extraxylary conductance. The absence of embolism reversal in B. blakeana suggests that embolization may be permanent without neutral or positive xylem pressure, but that the recovery of extraxylary conductance can be regained routinely in this species in the absence of root pressure.

Predicting the influence of subtropical trees on urban wind through wind tunnel tests and numerical simulations

Better prediction of turbulent airflow around urban trees is necessary because it impacts urban pollutant dispersion, outdoor thermal comfort, energy efficiency, pedestrian-level comfort and urban heat island mitigation. A major challenge is how to obtain an accurate numerical model of the turbulent flow field around trees and an improved parameterization of the turbulent momentum deficit using the drag coefficient (Cd). To address this challenge, we use wind tunnel tests and real trees to measure Cd for four common subtropical tree species: Ficus microcarpa, Mangifera indica, Michelia alba and Bauhinia blakeana. The results show that the Cd of the four trees ranges from 0.523 to 0.932, and that the negative relationship between Cd and wind speed (U) can be expressed by the exponential formula Cd=a*U−b. A three-dimensional model of wind modification by trees is proposed, and its accuracy is verified with wind tunnel measurements. With precise Cd and model, the predictability of the influence of trees on urban wind in subtropical areas is enhanced (root mean square error RMSE ranging from 2.89 m/s to 0.45 m/s). Future development and applications of the numerical model will help provide useful guidelines for urban landscape management and sustainable urban planning in terms of urban ventilation.

Modeling of shade creation and radiation modification by four tree species in hot and humid areas: Case study of Guangzhou, China

Shade creation and radiation modification by trees is an important way of alleviating the urban heat island and improving the outdoor thermal environment. However, a major challenge is still present in numerical models: How can shade creation and radiation modification by trees be realistically represented? To address this challenge, this paper proposes a new three-dimensional model of radiation modification by shade trees for four common tree species in Guangzhou, China: Ficus microcarpa, Mangifera indica, Michelia alba and Bauhinia blakeana. Its accuracy is verified with field measurements. The results show that the proposed model can accurately simulate the canopy attenuation of incoming solar radiation (SR) (d = 0.76∼0.93) and long-wave radiation (LWR) (RMSE = 2.7 W/m2∼12 W/m2) in the case of Ficus microcarpa, Mangifera indica, and Bauhinia blakeana. But for Michelia alba, the difference between measured and simulated values can be large (>60 W/m2), leading to a high RMSE (25 W/m2 ∼194 W/m2). The predictability of surface energy budget and thermal comfort in urban environments is enhanced by incorporating the proposed model into a heat balance model to obtain the mean radiant temperature (MRT). Future development and application of this numerical model will provide useful guidelines for urban landscape management and sustainable urban planning in terms of heat island mitigation.

Influence of trees on the outdoor thermal environment in subtropical areas: An experimental study in Guangzhou, China

Tree morphology and characteristics are quite different among different tree species, leading to large differences in cooling performance across tree species, particularly across different climatic regions. To obtain microclimatic characteristics and data on the influence of common subtropical tree species on the outdoor thermal environment, this study investigates, with field measurements, three physiological indices (leaf transpiration rate, leaf surface temperature, and leaf reflectance) and seven microclimatic parameters (solar radiation, long wave radiation, mean radiant temperature (Tmrt), ground surface temperature, air temperature, relative humidity, and wind speed) characterizing four common tree species in Guangzhou: Ficus microcarpa, Mangifera indica, Michelia alba, and Bauhinia blakeana. The Physiological Equivalent Temperature (PET) is calculated with the Rayman 12 tool to assess human thermal comfort. Special focus is set on the differences between these parameters in the presence and absence of tree cover. The results are as follows: Ficus microcarpa has the best cooling performance (reduced solar radiation by 1050 W/m2, reduced Tmrt by 14.8 °C, reduced PET by 32.4 °C). These trees have also some negative effects: reducing wind speed (2.83 m/s) and increasing long wave radiation (55 W/m2). It is expected that these data and results will shed some light on tree planting implications in subtropical areas.

Evaluation of the ENVI-Met Vegetation Model of Four Common Tree Species in a Subtropical Hot-Humid Area

Urban trees can significantly improve the outdoor thermal environment, especially in subtropical zones. However, due to the lack of fundamental evaluations of numerical simulation models, design and modification strategies for optimizing the thermal environment in subtropical hot-humid climate zones cannot be proposed accurately. To resolve this issue, this study investigated the physiological parameters (leaf surface temperature and vapor flux) and thermal effects (solar radiation, air temperature, and humidity) of four common tree species (Michelia alba, Mangifera indica, Ficus microcarpa, and Bauhinia blakeana) in both spring and summer in Guangzhou, China. A comprehensive comparison of the observed and modeled data from ENVI-met (v4.2 Science, a three-dimensional microclimate model) was performed. The results show that the most fundamental weakness of ENVI-met is the limitation of input solar radiation, which cannot be input hourly in the current version and may impact the thermal environment in simulation. For the tree model, the discrepancy between modeled and observed microclimate parameters was acceptable. However, for the physiological parameters, ENVI-met tended to overestimate the leaf surface temperature and underestimate the vapor flux, especially at midday in summer. The simplified calculation of the tree model may be one of the main reasons. Furthermore, the thermal effect of trees, meaning the differences between nearby treeless sites and shaded areas, were all underestimated in ENVI-met for each microclimate variable. This study shows that the tree model is suitable in subtropical hot-humid climates, but also needs some improvement.

Calcium distribution during pollen development in Bauhinia blakeana

Key message In this manuscript, we first found calcium induces vacuoles formation from mitochondria during microspore development in Bauhinia blakeana, which is not reported yet.

元谋干热河谷一种景观树种羊蹄甲的光合特性研究

通过对羊蹄甲的光合速率、气孔导度及其相应环境因子的测定，探讨元谋干热河谷羊蹄甲的光合生理生态特征。本研究采用TPS-1 (英国PPsystems公司出品)便携式光合测定系统对元谋县县城绿化树羊蹄甲的光合特性进行了研究，结果表明：羊蹄甲净光合速率的日变化成双峰曲线，光照强度(PAR)、蒸腾速率(Tr)、胞间CO2浓度(CI)、大气CO2浓度(Ca)、气孔导度(GS)、温度(T)等因子都会影响羊蹄甲的净光合速率，羊蹄甲对光能的利用率平均值为0.03 mmol∙mol−1，对水分的利用率平均为2.061 mmol∙mol−1。羊蹄甲在元谋干热河谷有较强的适应性。 In order to study the photosynthetic characteristics of Bauhinia blakeana, the photosynthetic rate, stomatal conductance and its corresponding environmental factors were measured. Photosynthetic characteristics of Bauhinia blakeana, a kind of greening tree species in Yuanmou County, were measured by using TPS-1 portable photosynthetic measurement system (produced by PPsystems Company in the British). The results showed that the daily variation of net photosynthetic rate of Bauhinia blakeana showed bimodal curve. The factors of photosynthetic active radiation (PAR), transpiration rate (Tr), intercellular CO2 concentration (Ci), atmospheric CO2 concentration (Ca), stomatal conductance (Gs) and temperature (T) impacted on the net photosynthetic rate of Bauhinia blakeana. The average value of light use efficiency was 0.03 mmol∙mol−1, and water use efficiency was 2.061 mmol∙mol−1. Bauhinia blakeana had stronger adaptation in Yuanmou dry-hot valleys.

Kernal Based Semi-Supervised Clustering and its Application in Leave Recognition of Bauhinia Blakeana Leaves

A novel kernel based semi-supervised fuzzy clustering algorithm is proposed, and its iterative formula is given. This new algorithm can effectively improve the efficiency of the clustering algorithm. Combined with Fisher projection algorithm, two principal components are extracted from 7 hue statistics and 11 green value statistics, this new semi-supervised clustering method is applied to recognize the angular leaf spot disease of Bauhinia blakeana. The results showed that the consistent rate is 100% for the labeled leaves, and above 95% for other unlabeled leaves.

The dust retention capacities of urban vegetation—a case study of Guangzhou, South China

Urban vegetation increasingly plays an important role in the improvement of the urban atmospheric environment. This paper deals with the dust retention capacities of four urban tree species (Ficus virens var. sublanceolata, Ficus microcarpa, Bauhinia blakeana, and Mangifera indica Linn) in Guangzhou. The dust-retaining capacities of four tree species are studied under different pollution intensities and for different seasons. Remote sensing imagery was used to estimate the total aboveground urban vegetation biomass in different functional areas of urban Guangzhou, information that was then used to estimate the dust-retaining capacities of the different functional areas and the total removal of airborne particulates in urban Guangzhou by foliage. The results showed that urban vegetation can remove dust from the atmosphere thereby improving air quality. The major findings are that dust retention, or capture, vary between the four species of tree studied; it also varied between season and between types of urban functional area, namely industrial, commercial/road traffic, residential, and clean areas. Dust accumulation over time was also studied and reached a maximum, and saturation, after about 24days. The overall aboveground biomass of urban vegetation in Guangzhou was estimated to be 52.0 × 10(5)t, its total leaf area 459.01km(2), and the dust-retaining capacity was calculated at 8012.89t per year. The present study demonstrated that the foliage of tree species used in urban greening make a substantial contribution to atmospheric dust removal and retention in urban Guangzhou.

广州市常见行道树种叶片表面形态与滞尘能力

以广州市常见的18种行道树为对象,通过扫描电镜观察比较了行道树的叶表面形态结构、应用接触角测定仪测定了绿化树种叶片的接触角对滞尘能力的影响。结果表明:不同树种的滞尘量差异显著,18种植物叶片雨后第26天的最大滞尘量在0.066-1.831g/m²,物种间相差达27倍以上。叶表面具有网状结构,气孔密度较大(20<气孔密度<60个)且气孔开口较大(如芒果)容易滞留粉尘;叶表面平滑具有蜡质层,气孔排列整齐,无明显起伏(如红花羊蹄甲、桃花心木、大叶紫薇、鹅掌藤),滞尘能力较弱。植物叶片接触角与滞尘量呈负相关(<em>r</em>=-0.614),接触角<90°的表现为亲水性。易润湿的植物叶片雨后第26天最大滞尘量在1.0-1.831g/m²,叶片表面的形态结构凹凸不平,具有钩状或脊状褶皱、突起等且20<气孔密度<60范围内,测得的接触角较小(芒果、重阳木、高山榕),使得粉尘与植物叶片接触面积较大,粉尘不易从叶面脱落,滞尘能力较强。而接触角较大的盆架树、麻楝、大叶紫薇、鹅掌藤和红花羊蹄甲的滞尘量均<1.0g/m²,其特殊的表面结构和疏水的蜡质使颗粒物不易吸附在植物叶片上,因此滞尘能力较弱。由此可见,植物叶表面蜡质含量和气孔密度及其叶片接触角的大小是影响植物叶片滞尘能力的主要因素,在进行城市绿化时,适当考虑选择叶表面形态有利于滞尘的绿化树种,将可提高城市植被的环境效应。;In this study, we selected eighteen species of common street trees along main roads in Guangzhou Municipality to observe and compare their leaf surface morphology using Scanning Electron Microscopy (SEM), and to evaluate how the contact angle of water droplet on leaf surfaces measured by goniometer influence the dust-retaining capability. It was found that the maximum leaf dust-retaining capabilities per unit area of the eighteen species of trees 26 days after rainfall were 0.066-1.831g/m², indicating significant differences (up to 27 times) among different trees. The plants with network structure on leaf surface, having high stomatal density and large opening of stomata, such as <em>Mangifera Indica</em>, have strong dust-retaining capability; while those whose leaf surfaces are smooth and covered by epicuticular wax with stomata arranged regularly without obvious undulation, such as <em>Bauhinia blakeana</em>,<em> Swietenia mahogani</em>,<em> Lagerstroemia indica Linn</em>. and<em> Scheffera arboricola</em>, have poor dust-retaining capability. There was a significant negative relationship between leaf contact angle and dust-retaining capability (<em>r</em>=-0.614). Leaves with contact angle smaller than 90° demonstrate hydrophilicity. Their maximum dust-retaining capabilities 26 days after rainfall ranged from 1.0 to 1.831 g/m². For leaves with rugged morphological structure, hook or ridge-shaped rumple, prominence and stomata density ranging from 20 to 60, the measured contact angles are smaller, making the contact area between leaf and dust larger. Therefore, it is not easy for dust on such trees as <em>Mangifera Indica</em>, <em>Bischofia Polycarpa</em> and <em>Ficus altissima Bl.</em>, to detach from leaf surface and these species have a strong dust-retaining capability. On the contrary, the special surface structure and hydrophobic wax of tree leaves with larger contact angle, such as <em>Alstonia scholaris</em>,<em> Chukrasia tabularis</em>,<em> Lagerstroemia indica Linn.</em>,<em> Scheffera arboricola </em>and <em>Bauhinia blakeana</em>, make it difficult for dust particles to attach to leaves, resulting in small dust-retaining capabilities of less than 1.0g/m². This study has shown that the wax content of surface foliage, stomata density and contact angle of leaves are the three main factors controlling the dust-retaining capability. It is therefore advisable to consider choosing tree species whose leaf surface morphology enhances dust-retaining capability for urban greening and thus to improve the environmental effectiveness of urban vegetation.

The morphological structure of leaves and the dust-retaining capability of afforested plants in urban Guangzhou, South China

Air pollution is a serious health problem throughout the world, exacerbating a wide range of respiratory and vascular illnesses in urban areas. The mass artificial plantation is very helpful to absorb dust and reduce pollution for conservation of the urban environment. The foliar surface of plants is an important receptor of atmospheric pollutants. Therefore, selection of suitable plant species for urban environment is very important. The dust-retaining capability of urban trees in Guangzhou was determined at four different types of urban area, and the morphological traits of their leaves such as wax, cuticle, stomata, and trichomes were observed under a scanning electron microscope. It was determined that the dust-retaining capability of any given tree species is significantly different in the same place. Of the four studied tree species in the industrial area (IA) and commercial/traffic areas (CTA) type urban areas, the highest amounts of dust removed by Mangifera indica Linn was 12.723 and 1.482 g/m(2), respectively. However, in contrast, the equivalent maxima for Bauhinia blakeana is only 2.682 g/m(2) and 0.720 g/m(2), respectively. Different plant species have different leaf morphology. The leaf of M. indica has deep grooves and high stomata density which are in favor of dust-retained, and thus, their dust-retained capability is stronger, while B. blakeana has the cells and epicuticular wax with its stomata arranging regularly, resulting in poor dust catching capability. Leaf size was also shown to be related to dust capture for the four studied tree species. The dust removal capacity of individual tree species should be taken into account in the management of greening plantation in and around an urban area. It was also shown that temporal variation in dust accumulation occurred over the 28-day observation period and this was discussed. Furthermore, spatial contrasts in dust accumulation were evidenced by the data. This reflected the differing pollution loadings of the four urban-type areas. The highest amount of dust accumulation was associated with the industrial area in which shipyard and steelworks occurred whilst the lowest dust accumulation was associated with the grounds of the University which was the control area.

Generative and Sperm Cell Isolation inBauhinia blakeana(Fabaceae)

Bauhinia blakeana (Fabaceae) pollen is bicellular and contains only a vegetative and generative cell at anthesis. The pollen grain contents, including the generative cell, can be released in vitro following osmotic shock. In this study, when pollen grains were incubated in a 10% sucrose and 5%–15% polyethylene glycol 4500 (PEG 4500) medium, over 50% of the pollen grains germinated and formed a short pollen tube. However, the generative cell did not divide in in vitro pollen tubes. In vivo pollen tubes were induced to grow from the style using an in vivo—in vitro method. Sperm cells were subsequently isolated from broken pollen tubes.

Molecular Evidence for the Hybrid Origin of Bauhinia blakeana (Caesalpinioideae)

Bauhinia blakeana Dunn is the Hong Kong Special Administrative Region emblem and a popular horticultural species in many Asian countries. It was first described as a new species from Hong Kong almost a century ago. This plant is sterile and has long been considered a hybrid, possibly from two related species, B. purpurea and B. variegata. However, not much evidence based on molecular methods was available to support this hypothesis. In this study, sequences of internal transcribed spacer 1 (ITS1), rbcL and atpB-rbcL intergenic spacer for five Bauhinia species and two varieties of one of the species were determined and compared. There were two types of ITS1 sequences in B. blakeana, one indistinguishable from that of B. purpurea and the other one identical to that of B. variegata. This confirmed that B. blakeana was a hybrid of these two species. Chloroplast atpB-rbcL intergenic spacer sequence of B. blakeana was identical to that of B. purpurea, indicating that B. purpurea was the female parent. The hybridization event seemed to occur only recently and was a rare incident. Its occurrence was likely facilitated by interspecific pollen competition. It appeared that human efforts played a crucial role in the preservation and ubiquity of B. blakeana.

Hybrid origin of “Bauhinia blakeana” (Leguminosae: Caesalpinioideae), inferred using morphological, reproductive, and molecular data

Bauhinia blakeana (Leguminosae subfam. Caesalpinioideae tribe Cercideae), or the Hong Kong Orchid Tree, is of great horticultural value. It is completely sterile and is shown here to be the result of hybridization between the largely sympatric species, B. purpurea and B. variegata. Although the analysis of patterns of morphological variation revealed only a few examples of phenotypic intermediacy, study of intersimple sequence repeat (ISSR) markers enabled unequivocal identification of the parental species due to the presence of additive inheritance of alleles and the absence of any bands that are unique to B. blakeana. Investigation of aspects of the reproductive biology of the taxa furthermore revealed that the parental species are largely xenogamous, have flowering periods that overlap seasonally and temporally, and share common pollinators. Evidence is provided to show that B. blakeana is not naturally stabilized and is only maintained horticulturally by artificial propagation. It is therefore recommended that the hybrid be regarded as a horticultural cultivar rather than a naturally occurring species; a new cultivar name, Bauhinia 'Blakeana', is accordingly validated.