Same,same, but different: Drought and salinity affect BVOC emission rate and alter blend composition of urban trees

Drought and salt are key abiotic stressors in temperate cities. Biogenic volatile organic compound (BVOC) emissions, often dominated by trees, influence the urban troposphere and mediate plant-plant and plant-insect interactions. While knowledge on constitutive BVOC emissions is increasing, modulation of blends by stress has yet received little attention. We thus investigated BVOC blends and herbivore-related subsets (‘bouquets’) of Quercus robur, Fagus sylvatica, Betula pendula and Carpinus betulus seedlings under control, and after 2-weeks of drought and salt stress using PTR-Tof-MS. 22 BVOCs were related to metabolic pathways, and changes among blends and bouquets were assessed. Drought led to a slight increase of isoprene and monoterpene emissions from Q. robur and F. sylvatica, respectively, while total non-isoprene emissions generally declined under water stress. Both drought and salinity led to distinct, species-specific changes in the emission rates of single BVOCs, and resulted in markedly different herbivore-related bouquets in F. sylvatica and C. betulus. Oxygenated VOCs and green leaf volatiles in particular increased in these two salt-sensitive species, while pathway-specific effects were less clear under drought. Findings indicate significant consequences of common urban stressors on BVOC emission spectra, including tropospheric ozone formation and severely hampered plant communication cues under stress.     

Genotypic variation in water relations and gas exchange of urban trees in Detroit,Michigan, USA

Increasing tree species diversity has become a key underpinning for communities to improve resilience of urban and community forests. Increasingly, urban forestry researchers are examining physiological traits to aid in selecting trees for urban sites. Knowledge of physiological responses also has implications for understanding species’ resilience to increased stresses associated with climate change. Here, we compare growth, leaf SPAD chlorophyll index, water relations, and gas exchange of seven genotypes of shade trees planted in two locations in downtown Detroit, MI, USA. Genotypes included Redpointe® maple (Acer rubrum ‘Frank Jr.’), Flashfire® maple (Acer saccharum ‘JFS-Caddo2′), Pacific Sunset® maple (Acer truncatum x platanoides ‘Warrenred’), Emerald City® tulip tree (Liriodendron tulipifera ‘JFS-Oz’), Chanticleer® pear (Pyrus calleryana ‘Glen’s Form’), swamp white oak (Quercus bicolor), and Emerald Sunshine® elm (Ulmus propinqua ‘JFS-Bieberich’). Trees were planted in either Lafayette Plaisance Park (Park), a large urban greenspace, or on the median of St. Aubin Avenue (Median), a nearby major thoroughfare. Tree height growth and leaf SPAD index were higher for trees planted in the Park location than on the Median. However, genotypic variation was larger than the effects of location or the interaction of Genotype × Location for most traits. Across measurement dates, midday leaf water potential was lowest for Pyrus trees and highest for Ulmus and Liriodendron trees. Pyrus and Quercus trees had relatively high rates of net photosynthesis (A) and stomatal conductance (g_s) while Liriodendron, Acer saccharum, and Ulmus trees had low rates of A and g_s. Liriodendron trees closed their stomata rapidly as leaf water potential (Ψ_w) declined (isohydric response), while Pyrus and Quercus trees maintained g_s across a range of leaf Ψ_w (anisohydric response). Liriodendron trees also had the highest relative growth rates, suggesting that drought stress avoidance through isohydry is a viable drought tolerance mechanism in urban trees.     

Testing the suitability for coastal green areas of three ornamental shrub species through physiological responses to the saline nebulization

Besides abiotic constraints, plants along the coastal urban areas must face additional cues such as saline aerosol, which impact net plant CO₂ assimilation (P_n), reducing biomass and influencing their aesthetic features. In this study, three species (Photinia × fraseri, P; Escallonia rubra, E; and Feijoa sellowiana, F) were subjected to saline nebulization (SN) with a 100 mM NaCl solution. Analyses were performed at 0, 10, and 20 days by monitoring the ion accumulation in plant organs, leaf osmotic potentials, gas exchange, chlorophyll a fluorescence parameters, and chlorophyll contents. Overall, E-SN plants absorbed more Na⁺ and Cl⁻ in leaves than P-SN and F-SN ones. This phenomenon was influenced by leaf ‘wettability’ features such as the contact angle of water droplets, droplet retention, and water storage capacity, and the effectiveness of translocating these ions on twig tissues. SN increased the leaf osmotic potential (regardless of species). At 10 days (i.e., moderate stress conditions), P_n declined in all SN species, but more severely (−82 %) in E-SN plants. The observed P_n reductions were due to different limiting factors according to the plant species: P_n was reduced by non-stomatal limitations in P-SN plants, stomatal closure in F-SN, and a combination of both in E-SN individuals. At 20 days (i.e., severe stress conditions), in all SN-plants, lower values in all the physiological parameters than controls were observed, indicating a low tolerance to prolonged SN. The work shows that non-destructive physiological measurements provide a reliable assessment of plant tolerance to SN, which can help growers to select ornamental species suitable for coastal green areas.     

Drought responses of six ornamental herbaceous perennials

Although low water use landscaping is becoming common in arid regions, little is known about drought tolerance and drought responses of many ornamental plants, especially herbaceous perennials. Drought responses were assessed for six herbaceous ornamental landscape perennials in a 38 l pot-in-pot system in northern Utah over a 2-year period. The first year was an establishment period. During the second year, drought responses were evaluated for established Echinacea purpurea (L.) Moench, Gaillardia aristata Pursh, Lavandula angustifolia P. Mill., Leucanthemum × superbum (J.W. Ingram) Berg. ex Kent, ‘Alaska’, Penstemon barbatus Roth var. praecox nanus rondo, and Penstemon × mexicali Mitch. ‘Red Rocks’. Plants were irrigated at frequencies of 1 (control), 2, or 4 weeks between June and September, simulating well-watered conditions, moderate drought, or severe drought. Osmotic potential (Ψ_s), gas exchange, visual quality, leaf area, and dry weight were assessed. In a confined root zone, P. barbatus showed the greatest tolerance to all levels of drought, avoiding desiccation by increasing root:shoot ratio and decreasing stomatal conductance as water became limiting. L. angustifolia and P. × mexicali showed tolerance to moderate drought conditions, but died after exposure to the first episode of severe drought. Neither G. aristata nor L. superbum were able to regulate shoot water loss effectively. Instead, both species displayed drought avoidance mechanisms, dying back when water was limiting and showing new growth after they were watered. Compared to control plants, G. aristata shoot dry weight was reduced by 50% and 84%, and L. superbum shoot dry weight was reduced by 47% and 99% for the 2- and 4-week irrigation intervals, respectively. Root dry weights were affected similarly for both species. E. purpurea exhibited poor visual quality at all irrigation intervals, in particular wilting severely in both drought treatments, but regaining turgor when watered again. P. barbatus is recommended for ornamental landscapes that receive little or no supplemental irrigation, while E. purpurea is not recommended for low water landscapes because of low visual quality under even mild drought.     

瓜类蔬菜幼苗对辣椒疫霉菌的抗病性鉴定

以10种瓜类蔬菜幼苗为材料,在其2片真叶展平时,分别以孢子浓度为2×103、2×104、2×105个.mL-1的辣椒疫霉菌游动孢子悬浮液进行了人工灌根接种和苗期抗病性鉴定。结果表明,不同瓜类蔬菜品种幼苗对辣椒疫霉菌的抗病性表现完全不同,其中早熟1号肉丝瓜和新秀丝瓜幼苗未感染辣椒疫霉菌;其余9种瓜类蔬菜幼苗随着接种辣椒疫霉菌游动孢子浓度的提高而抗病性降低,在接种辣椒疫霉菌游动孢子浓度为2×104个.mL-1时,蜜本南瓜和新广优节瓜幼苗抗病性较强,早优苦瓜和碧峰黄瓜中度抗病,特大新红宝西瓜、秀美青筋白瓜、银辉薄皮甜瓜、台优蒲瓜和晶莹1号西葫芦高度感病。     

Sana Physiological responses of two grapevine (Vitis vinifera L.) cultivars to CycocelTM treatment during drought

The plant growth regulator Cycocel^TM [(2-chloroethyl)trimethylammonium chloride] can be used to produce drought tolerance in grapevine (Vitis vinifera L.) due to a reduction in the ratio between vegetative growth and fruit production. To evaluate the physiological responses of two grapevine cultivars to drought and Cycocel^TM treatment, a factorial experiment was conducted in a greenhouse. The factors included irrigation frequency (at 5-, 10-, or 15-day intervals corresponding to no, mild, or severe drought stress), Cycocel^TM concentration (0, 500, or 1000 mg l^–1), and cultivar (‘Rasheh’ or ‘Bidane-Sefid’). Stomatal conductance (g_s) the net rate of CO₂ assimilation (A_net), the rate of transpiration (T_r), and chlorophyll a and b concentrations decreased in plants exposed to mild or severe water-deficit stress, whereas carotenoid, proline, and total soluble sugar concentrations increased compared to plants with no drought stress. The relative water content (RWC) of leaves declined only under severe drought stress. A reduction in intercellular CO₂ concentrations (C_i) occurred under mild drought stress; however, under severe drought stress, C_i values increased. Under mild drought stress, the reduction in the net rate of photosynthesis was related to stomatal closure, whereas under severe drought stress, non-stomatal factors were dominant. Water-use efficiency (WUE) improved under mild drought stress relative to non-stressed plants, but under severe drought, it declined. Foliar applications of Cycocel^TM resulted in increased A_net, g_s, T_r, and WUE values, as well as proline and soluble sugar concentrations. ‘Rasheh’ was more tolerant to drought stress than was ‘Bidane-Sefid’. Foliar applications of Cycocel^TM, particularly at 1000 mg l^–1, mitigated the negative effects of drought stress by increasing A_net, WUE, RWC, compatible solute concentrations, such as proline, soluble sugar, and chlorophyll a and b concentrations.     

Effect of pruning and plant spacing on the growth of cherry rootstocks and their influence on stem water potential of sweet cherry trees

Summary

The aims of this work are to describe the effects of pruning and planting density on growth and water relations of ungrafted and grafted sweet cherry trees. A trial with cherry rootstocks ‘Prunus avium’, ‘CAB 11E’, ‘Maxma 14’, ‘Gisela 5’ and ‘Edabriz’ was begun in 1997. Pruning severities were applied to the rootstocks (0, 30, 60 and 90% of the vegetative growth was removed corresponding to P1, P2, P3 and P4 treatments, respectively) after planting to two plant spacings (S1 = 0.25 × 1.0 m and S2= 0.45 × 1.5 m). Canopy, root growth and leaf water potential (ψ_leaf) were quantified throughout the growing season. Pruning significantly affected root length and root weight of the rootstocks. Uncut plants (P1) showed a heavier and expanded root biomass (231 g and 108 m) than the intensively pruned plants (P4) (187 g and 75 m). The greater root biomass was obtained with the spacing/pruning combination, S1/P1 (285 g), and the smaller with S1/P4 (180 g) and S2/P4 (176 g). ψ_leaf varied significantly between the rootstocks and plant spacing but not with pruning. ‘Maxma 14’ and ‘P. avium’ attained the lowest values of midday ψ_leaf, –2.28 and –2.04 MPa, but the highest values of predawn ψ_leaf, –0.29 and –0.25 MPa, respectively. Generally, with high density (S1), the rootstocks exhibited lower predawn and midday ψ_leaf. In 1998, cultivars ‘Burlat’, ‘Summit’ and ‘Van’ were grafted onto rootstocks and a trial was installed in 1999. Predawn and midday stem water potential (ψ_stem) on cherry trees, measured in 2002, were affected significantly by the rootstock/genotype combination. Cultivars grafted on ‘P. avium’ and ‘Maxma 14’ showed the less negative midday ψ_stem, –1.36 and –1.42 MPa respectively, so these rootstock genotypes perhaps induced a higher drought resistance to the scion. Recorded data show that the scion-rootstock interaction with regard to production performance under water deficits may be an important consideration in cherry tree planting strategies.     

Effect of native habitat on the cooling ability of six nursery-grown tree species and cultivars for future roadside plantings

Vegetation in urban areas provides benefits to people, which are increasingly assessed and valued as ecosystem services (ESS). The regulation of the urban microclimate is one of these services, since trees have the potential to reduce urban heat loads by evapotranspiration and shading. Simultaneously, it has been suggested that trees from dry habitats should be used to cope with the increasing risks of drought under climate change in Central Europe. The underlying properties that enable those trees to reduce dependence on the environment, however, are assumed to come at the expense of biomass production and water loss. In the potentially conflicted area between drought tolerance and ESS we compared water consumption, water-use efficiency (WUE), crown structure and growth of six roadside species/cultivars, which are assumed to vary in drought tolerance, due to differing resource supplies in their native habitats. Acer platanoides, Carpinus betulus ‘Fastigiata’, and Tilia cordata ‘Greenspire’ were compared with Acer campestre, Ostrya carpinifolia, and Tilia tomentosa ‘Brabant’, the latter presumably being less water-demanding. Measurements took place in the municipal nursery of Munich during summer 2016.Surprisingly, the less water-demanding species/cultivars exhibited on average 1.24 times higher values of maximum daily sap flux density and up to seven times higher growth rates, both contributing to higher WUE. Scaled to leaf level, however, their mean daily transpiration rates were on average lower (0.21 and 0.31 kg H₂O m⁻² d⁻¹, respectively). They also showed higher flexibility in response to changing weather with increased growth and transpiration under favorable conditions in early summer, but a more conservative water use in dry late summer. The results suggest that these species/cultivars tend to regulate their water use stronger under increasing dryness, whereas canopy size and leaf amount are still the main important determinants of species and cultivar differences in water use.     

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.     

Detecting different levels of drought stress in apple trees (Malus domestica Borkh.) with selected biochemical and physiological parameters

Rational irrigation scheduling based on sensing drought stress directly in plants is becoming more important due to increasing worldwide scarcity of fresh water supplies. In order to evaluate a set of potential biochemical and physiological stress indicators and select the best drought stress markers in apple trees, two experiments with potted trees and an experiment with intensive orchard grown apple trees ‘Elstar’ and ‘Jonagold Wilmuta’ were conducted in early summer in tree following years. Biochemical parameters: ascorbic acid, glutathione, tocopherols, chlorophylls, carotenoids, free amino acids, soluble carbohydrates, and physiological parameters already known as stress indicators in apple trees: predawn and midday leaf water potential, net photosynthesis (Pn), stomatal conductance (g_s), transpiration (Tr) and intercellular CO₂ concentration (Ci) were measured in leaves of apple trees subjected to different intensities of slowly progressing drought or no drought. Our study pointed out zeaxanthin and glutathione as the best drought stress markers in apple trees. Ascorbate and sorbitol appeared to be reliable indicators of moderate drought only. Responses of other tested biochemical parameters were not consistent enough to prove their role as drought stress markers in apple trees. Relative air humidity should be taken in consideration when physiological parameters g_s, Pn, Tr and Ci are used as drought stress markers in apple trees. Our study revealed that in situations where low relative air humidity affects g_s and with g_s connected physiological parameters, biochemical markers may be better tool for determination of drought stress intensities in apple trees.     

Influence of growth regulators on setting,retention and weight of fruits in two cultivars of litchi

Investigations were undertaken to explore the possibility of improving setting, retention and weight of fruits in ‘Early Seedless’ and ‘Calcuttia’ cultivars of lichi (Litchi chinensis) by means of growth regulators. Indole acetic acid (IAA) at 20, 40 and 80 mg l^?1, 2,4-dichlorophenoxy acetic acid (2,4-D) at 2,4 and 8 mg l^?1 and gibberellic acid (GA₃) at 50, 100 and 150 mg l^?1 were sprayed on panicles in the first fortnight of April, when 50–100% flowers had opened. All 3 growth regulators caused a favourable effect on fruit setting, fruit retention and weight of individual fruits, but IAA at 20 mg l^?1 proved the best for enhancing setting, GA₃ at 50 mg l^?1 for increasing retention and GA₃ at 100 mg l^?1 for improving fruit weight. IAA and GA₃ should, therefore, be used in combination. Between the 2 cultivars tested, ‘Calcuttia’ proved superior to ‘Early Seedless’ in fruit setting, fruit retention and weight of individual fruits.     

中国葡萄属野生种及其种间F1 代抗旱性鉴定初探

 在盆栽干旱胁迫条件下, 测定了中国葡萄属野生种8 个种的11 个株系及野生种燕山葡萄与美洲种河岸葡萄杂交F1 代的叶片失绿黄化程度、相对含水量和原生质体细胞膜透性, 并以这3 项指标综合评价中国葡萄属野生种及其种间F1 代的抗旱性。结果表明, 中国葡萄属野生种中: 燕山葡萄燕山- 1 为高抗类型; 葡萄泰山- 1 为中抗类型; 葡萄安林- 2、山葡萄泰山- 11、秋葡萄江西- 2 和平利- 7、复叶葡萄甘肃- 91 和南郑- 2、毛葡萄渭南- 3、华东葡萄广西- 1 为低抗类型; 刺葡萄塘尾为不抗类型。燕山- 1 ×河岸葡萄杂交F1 代的抗旱性表现为连续分离现象, 个别杂种单株的抗旱性表现为超亲遗传。     

An index to identify suitable species in urban green areas

This paper presents a method that allows sorting of tree and shrub species according to their suitability for planting in urban areas of Madrid (Spain). Suitability was determined from a weighted index for each species according to the severity of damage (biotic, abiotic, and anthropogenic; stem wounds are the main problem in trees, while dead plants are the most important problem in shrubs, seasonal flowers, and vines) and to risk, which was obtained from a new measure, observed Species per Green Area per Year (SAYs). The greater the number of damaged SAYs, the less suitable a species was considered for outdoor planting. For this purpose, 49 green areas corresponding to 141 ha were sampled during 2005–2008. The tree species least recommended for planting include Robinia pseudoacacia, Ulmus sp., Acer negundo, Platanus × hybrid, Populus Boolleana. The shrubs least recommended for planting are Nerium oleander, Cotoneaster sp., Euonymus europaeus, Pyracantha coccinea, and Pittosporum tobira. Statistical analysis reveals that native species have a lower percentage of damaged SAYs than non-native species.     

Wood hydraulic and mechanical properties induced by low water availability on two ornamental species Photinia × fraseri var. Red Robin and Viburnum opulus L.

Deficit irrigation at the nursery stage induces drought acclimation through the establishment of avoiding mechanisms and hardening processes. In this experiment, we hypothesized that water deficit would affect wood hydraulic conductivity and mechanical properties with effects on the leaf water potentials of two ornamental species, Photinia × fraseri var. Red Robin and Viburnum opulus L.The experiment was conducted in a nursery (Pistoia, Italy) during summer 2011. Individuals were arranged in three plots under three watering regimes. The control plot (C) received an amount of water replacing that lost via evapotranspiration, while two plots were maintained under severe water deficit (SWD = 33% C) and moderate water deficit (MWD = 66% C).Water deficits reduced stem diameter in both species without changing wood density (D). Concerning mechanical properties, stiffness (E) and strength (YS) of Photinia resulted higher in Photinia than in Viburnum, which did not show differences between treatments in either E or YS, whereas in Photinia, E was lower in SWD (P < 0.05) than in C. Photinia was also characterized by higher k without significant differences between treatments while Viburnum showed a lower conductivity and a significant reduction of k_h under SWD (P < 0.05). Despite this, in field conditions the two species had similar behaviour concerning the leaf water status, showing a reduction of Ψ under SWD.A longer acclimation period would probably be necessary to induce major changes in wood mechanical properties, but the similarity of responses on leaf water status in MWD and C might indicate that a reduction to 66% of water need might be sufficient to maintain the level of turgor necessary for plant physiological functioning.     

Solar radiation intensity influences extensive green roof plant communities

Two studies were conducted on a third-story rooftop to quantify the effect of solar radiation (full sun versus full shade) on several US native and non-native species for potential use on extensive green roofs. In the first study, plugs of six native and three non-native species were planted in May 2005 on substrates of two different depths (8.0 and 12.0 cm) both in sun and shade. Absolute cover (AC) was recorded using a point-frame transect during the growing season beginning in June 2005 and every 2 weeks thereafter for a period of 4 years. By week 174 (23 September 2008), most species exhibited different AC within a depth between sun and shade. However, when all species were combined, overall AC did not differ between sun and shade within a depth. This indicated that while species make-up was changing among solar radiation levels, that overall coverage was not significantly different between sun and shade. For all substrate depths and solar levels, the most abundant species were Sedum acre, Allium cernuum, Sedum album ‘Coral Carpet’, and Talinum calycinum. Less abundant species included Talinum parviflorum, Carex flacca, Sedum stenopetalum, and Sedum divergens, which all exhibited 0 or near 0 AC regardless of depth or solar radiation levels. With the exception of T. calycinum, native species were less abundant than non-native species.In the second study, six common extensive green roof species of Sedum established from seed in May 2005 on a 10.0 cm (3.9 in) substrate depth were compared in both sun and shade over four growing seasons. AC was evaluated as in the previous study. Solar radiation did not affect AC, but overall species composition differed between sun and shade levels. The most abundant species in full sun were S. acre (0.57 AC) and S. album ‘Coral Carpet’ (0.51 AC). Sedum kamtschaticum (0.57 AC) and Sedum spurium ‘Coccineum’ (0.35 AC) performed the best in the shade. For both solar levels, the least abundant species at week 174 were Sedum pulchellum (0.0 AC) and S. album ‘Coral Carpet’ (0.1 AC).     

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.     

Stomatal regulation and xylem cavitation in Clementine (Citrus clementina Hort) under drought conditions

Summary

In many trees species, a strong relationship exists between stomatal closure and the onset of cavitation in xylem vessels. This relationship was investigated in a Citrus species. Young potted ‘Clementine’ (Citrus clementina Hort ‘Clementine’) grafted on ‘Carrizo Citrange’ (Citrus sinensis × Poncirus trifoliata) or ‘Trifoliate Orange’ (Poncirus trifoliata Raf), and grown under greenhouse conditions, were submitted to periods of drought by withholding irrigation. Pre-dawn water potential, leaf stomatal conductance, plant transpiration, the degree of xylem embolism, and xylem vulnerability curves were measured. Transpiration and stomatal conductance were reduced to a minimum value when the pre-dawn water potential reached -1 MPa. This value corresponded to the threshold pressure below which cavitation was induced. Higher intensities of water stress provoked more cavitation, but the degree of xylem embolism, as measured by percentage loss of conductivity, always remained below 50%. ‘Clementine’ is therefore vulnerable to embolism, but early stomatal regulation prevents the occurrence of embolism. Under severe water stress, ‘Clementine’ is able to maintain functional xylem vessels, which probably enhances its survival during periods of intense drought, and favours its recovery. This suggests that xylem cavitation is a key process in understanding the response of Citrus to drought and, hence, is a promising criterion by which to screen for more drought-tolerant genotypes.     

Acclimation to partial shading or full sunlight determines the performance of container-grown Fraxinus ornus to subsequent drought stress

Cultivation techniques in the nursery aimed to improve tolerance to abiotic stresses after planting in the landscape may have great ecological value. Here we tested the hypothesis that the irradiance at which plants grow in the nursery may impact on their responses to a subsequent drought stress. Measurements of relevant morpho-anatomical, physiological and biochemical traits were conducted in Fraxinus ornus, a member of the Oleaceae family of increasing interest as an urban tree. Leaves developed under moderate shade displayed a lower ability to preserve water balance, thus suffering from a greater decline in net CO₂ assimilation than leaves acclimated to full sunlight, when subsequently exposed to drought stress. Shaded leaves also displayed an inherently lower capacity to dissipate excess radiant energy through nonphotochemical quenching, thus suffering from greater oxidative damage than sun leaves under drought. These results indicate that sunlight irradiance at which container-grown ash trees grow in the nursery may tightly affect the tolerance to subsequent drought stress. This may have great value for enhancing the establishment of container-grown plants in the landscape, as fully leaved plants may suffer from severe drought stress during early stages of acclimation in the landscape.     

Rootstock influence on leaf and fruit mineral status of ‘Bartlett’ and ‘d'Anjou’ pear

In a test with ‘Bartlett’ and ‘d'Anjou’ pear on 8 Pyrus (P.) rootstocks, leaves of ‘Bartlett’ were high in S and Fe on ‘Bartlett’ seedlings (BS), in Zn on P. ussuriensis Maxim. seedlings (USS), and in B on seedlings of P. calleryana Decne (Cal). Leaves of ‘d'Anjou’ were high in P, Zn and B on BS, in N on USS, and in S on Cal. Both ‘Bartlett’ and ‘d'Anjou’ were high in K and Ca on P. betulaefolia Bunge seedlings (Bet). Fruit of both ‘Bartlett’ and ‘d'Anjou’ were high in N, K and Mg on Bet and Cal and high in Ca on Cal and USS. With both ‘Bartlett’ and ‘d'Anjou’, moderately high correlations were found between leaf and fruit concentrations of K and Mg; positive correlations were high for Ca and S with ‘Bartlett’ and for Zn and B with ‘d'Anjou’. There was a very high negative correlation between leaf and fruit Ca with ‘d'Anjou’.     

水分胁迫对蔓生紫薇和亮叶忍冬生长及生理特性的影响

 采用盆栽试验法, 研究水分胁迫对蔓生紫薇(Lagerstroemia indica‘Summer and summer’) 和亮叶忍冬(Lonicera nitida‘Maigrun’) 两种木本地被植物生长及生理特性的影响。结果表明: 水分胁迫下,两种植物的生长受到明显抑制, 蔓生紫薇受抑制程度高于亮叶忍冬, 其相对生长量远小于亮叶忍冬。水分胁迫使两种植物净光合速率、蒸腾速率、气孔导度下降, 胞间CO₂浓度则前期下降后期上升, 且表现为蔓生紫薇各生理指标的变化幅度大于亮叶忍冬。综合评价两种植物的抗旱性为: 亮叶忍冬> 蔓生紫薇。