Fraxinus Ornus Research Articles

Correlation of Field-Measured and Remotely Sensed Plant Water Status as a Tool to Monitor the Risk of Drought-Induced Forest Decline

Increased frequency of tree mortality and forest decline due to anomalous drought events calls for the adoption of effective monitoring of tree water status over large spatial and temporal scales. We correlated field-measured and remotely sensed plant water status parameters, to test the possibility of monitoring the risk of drought-induced dehydration and hydraulic failure using satellite images calibrated on reliable physiological indicators of tree hydraulics. The study was conducted during summer 2019 in the Karst plateau (NE Italy) in a woodland dominated by Fraxinus ornus L.; Sentinel-2 images were acquired on a seasonal scale on the same dates when absolute water content (AbWC), relative water content (RWC), and minimum water potential (Ψmin) were measured in the field. Plant water status parameters were correlated with normalized difference vegetation index (NDVI and NDVI 8A), normalized difference water index (NDWI), and soil-adjusted vegetation index (SAVI). Significant Pearson and Spearman linear correlations (α < 0.05) emerged between all tree-level measured variables and NDWI, while for NDVI, NDVI 8A, and SAVI no correlation was found. Our results suggest the possibility of using the NDWI as a proxy of tree water content and water potential.

Gestione forestale e prevenzione del dissesto idrogeologico in territori ad elevata vulnerabilità in Campania

This paper focuses on the compatibility between forest management and soil conservation with reference to chesnut (Castanea sativa Mill.), holm oak (Quercus ilex L.) and especially Manna Ash (Fraxinus ornus L.) mixed hop Hornbeam (Ostrya carpinifolia Scop.) coppices stands, located on slopes of Campania and characterized by intensely pedogenised pyroclastic coverage, but unstable when facing intense rainy events. Based on the Corine Land Cover system (2012), we divided the areas into the three physiognomic types; thus, the proportion of surfaces falling under the pyroclastic coverage, which are the more instable, were obtained by overlapping the land systems and soil map produced by the Campania region (2014). For each type of coppice, we examined all the different structural conditions (traditional coppices, coppices past traditional rotation age and coppice in conversion to high forest) and underlined the most important critical issues due to clearcutting, We summarized the different types of silvicultural interventions to improve the forest management sustainability, especially in those areas which are vulnerable to hydrogeological instability. We also stressed that forest planning is the essential tool for sustainable management of coppices, together with the catchment area and the fire-fighting planning.

Conversion of Pinus nigra Plantations with Natural Regeneration in the Slovenian Karst: The Importance of Intermediate, Gradually Formed Canopy Gaps

Since the mid-19th century, Pinus nigra plantations have played a key role in the restoration of degraded European landscapes. Nowadays, these plantations are aging and prone to natural disturbances, insect infestations, and diseases. For their successful gradual conversion, knowledge of optimal gap spatiotemporal dynamics is crucial. We studied herb and natural regeneration patterns along with site factors on 477 subplots within 44 plots distributed over four stand types: closed stand (14% diffuse light), open stand (21%), gap edge (23%), and gap (57%). Despite the abundant Quercus petraea, Q. cerris, and Q. pubescens mast year, no one-year seedlings were recorded, which is likely due to the summer drought. Short seedlings (h < 20 cm) of Quercus sp., Fraxinus ornus and Ostrya carpinifolia were more successful within closed stands. Short Quercus seedlings were positively associated with soil depth and negatively associated with soil nutrients, distance to seed trees, and Sesleria autumnalis coverage. Taller Quercus seedlings required more light than both of its strongest competitors and were positively related to humid soils and less rocky sites. Ungulate overbrowsing significantly impeded natural regeneration. The results indicate a satisfactory Quercus density for conversion and the importance of advanced regeneration, which should be gradually, but persistently, released by progressively widening gaps.

Coppice Forest Management Planning and the Regeneration Potential of Pure and Mixed Oak Coppice Forests in North Macedonia

Background and Purpose: Coppicing is the most widely used silvicultural system in North Macedonia and coppice forests together with shrubs cover cca. 69% of the forest cover area. Pure and mixed stands of oak coppice forests alone cover about 50% of the total forest area subject to current Forest Management Plans. In general, coppices are routinely managed, especially when coppicing as a system is planned to be continued. However, sustainability can be threatened if attention is not paid regarding the age of trees/stands and the presence of undesired tree species. The purpose of this study was to determine: (1) quantitative and qualitative aspects of planned management activities in oak coppices throughout the country, (2) the resprouting potential of over-mature oak coppices, and (3) their potential for generative regeneration. Materials and Methods : We analyzed all official forest management plans in the country, in order to assess planned activities and the methods of management. Additionally, 21 experimental plots were set in order to determine the resprouting potential of over-mature (85 to 95 years) coppices of Quercus petraea and Q. frainneto which previously have been subject of clear-cutting. We took a total count of sprouts on all experimental plots, while generative regeneration seedlings were counted on 4 schematically positioned subplots in each experimental plot. Sprouts and generative seedlings were categorized by height. Results and Conclusions: According to the data from forest management plans, coppicing is planned to remain as a management system on 401,636 ha, of the total of 450,975 ha of oak coppice forests. Indirect conversion to high forests is planned on 39,137 ha, while direct conversion with substitution is planned for 10,202 ha. In field trials, resprouting was registered on only 38% of the stools. Generative regeneration was recorded in both oak species in numbers which indicate good potential for conversion of oak coppice stands into high forests by seed felling. However, numerous sprouts of other species ( Corylus avellana, Fraxinus ornus, Acer heldreichii), which reach up to 3 meters in height within two seasons, are potentially dangerous for dominating oak seedlings.

Seven years of arboreal pollen monitoring in the İğneada waterlogged forests (NW Turkey)

This study was carried out in the İğneada Waterlogged Forests (Kırklareli) located downhill of Istranca mountains at 20 km distance to Bulgaria border line and had a shore to Black Sea. These forests have different vegetation types such as waterlogged forest, peat, bog and sand dunes plant communities, sand zone and wetlands. The main arboreal species of these forests are Acer campestre, Acer trautvetteri, Alnus glutinosa, Carpinus betulus, Carpinus orientalis, Fraxinus angustifolia, Fraxinus ornus, Juglans regia, Quercus cerris, Quercus frainetto, Quercus petraea, Quercus robur, Ulmus leavis and Ulmus minor. Pollen monitoring results were obtained from six different sampling sites in the waterlogged forests around Mert and Saka Lake. The purpose of this study is to determine the modern pollen distribution of these forests and to create a basic calibration scheme for the fossil pollen studies. For this purpose, seven years of modern pollen distribution was monitored between September 2009 and 2016 using Tauber pollen traps which were placed at 6 different points in this study area. These traps were changed once a year in the field and transferred to the Palynology Laboratory of Istanbul University-Cerrahpaşa. The protocol of European Pollen Monitoring Programme (EPMP) was followed in the laboratory methodology. The majority of the pollen influx obtained from the Tauber pollen traps in the İğneada Waterlogged forests belongs to Fraxinus and Carpinus from 2009 to 2016. As a result of this study, the annual arboreal pollen influxes of Fraxinus, Carpinus, Quercus, Acer, Corylus, Ulmus, Hedera helix and Alnus was higher respectively in the years of 2009-2016. Seven-year pollen influx data of these pollen traps reflects the current vegetation.

Non-structural carbohydrate and hydraulic dynamics during drought and recovery in Fraxinus ornus and Ostrya carpinifolia saplings

The maintenance of hydraulic function during and after a drought event is crucial for tree survival, but the importance of non-structural carbohydrates (NSCs) in the recovery phase is still debated. We tested whether higher NSC availability facilitates post-drought hydraulic recovery, by applying a short-term drought (Sdr) and a long-term drought combined with shading (Ldr+sh) in Fraxinus ornus and Ostrya carpinifolia. Plants were then re-irrigated and recovery was checked 24 h later, by measuring water potential, stem percentage loss of hydraulic conductance (PLC) and NSC content. The relative magnitude of hydraulic and carbon constraints was also assessed in desiccated plants. During drought, PLC increased only in F. ornus, while it was maintained almost constant in O. carpinifolia due to tighter stomatal control of xylem pressure (i.e. more isohydric). In F. ornus, only Sdr plants maintained high NSC contents at the end of drought and, when re-irrigated, recovered PLC to control values. Whereas hydraulic failure was ubiquitous, only F. ornus depleted NSC reserves at mortality. Our results suggest that preserving higher NSC content at the end of a drought can be important for the hydraulic resilience of trees.

Phytoplasmas associated with declining of hazelnut (Corylus avellana) in Slovenia

Hazelnut (Corylus avellana) is cultivated on 118 ha and ranks eighth in Slovenian fruit growing production, representing 2.8% of the total area of fruit plantations in the country. However, decline of some of the trees appeared in 2012 in two plantations located in eastern Slovenia. Together these orchards cover 5 ha, with around 1600 trees planted 12 to 15 years ago. By October 2018, ~12% of these trees had died, and an additional 12% showed decay symptoms. The dead and dying trees were scattered throughout both orchards, with no apparent pattern. The most affected cultivar was ‘Istrska dolgoplodna leska’. Using molecular diagnostic methods, we showed infection of symptomatic trees with three unrelated phytoplasmas: ‘Candidatus Phytoplasma fragariae’, of the 16SrXII-E phytoplasma subgroup, and phytoplasma of the 16SrV and 16SrIX groups. In 2018, the presence of ‘Ca. P. fragariae’ and/or phytoplasma of 16SrV group were confirmed in decayed hazelnut trees in eastern, north-eastern, central, south-eastern and western Slovenia. ‘Ca. P. fragariae’ has also been detected in a forest in south-western Slovenia, for Acer campestre, Carpinus betulus, Crataegus laevigata, Fraxinus ornus and Quercus petraea. All infected forest trees showed unusual dense proliferation of sprouts from roots and/or trunks. Molecular characterisations of partial 16S rRNA, secY, map and ribosomal protein genetic locus of hazelnut 16SrV phytoplasma isolates show that they are identical to isolates that can cause grapevine flavescence dorée disease. Here, the results of our recent study and the open questions on this burning issue for hazelnut production are presented.

Efecto de la luz y la humedad del suelo sobre variables fisiológicas en seis especies forestales mediterráneas plantadas bajo dosel de pinar

Introduction: Resprouter species, by regenerating rapidly, can maintain an optimal carbon balance and improve the resilience of ecosystems that have been disturbed or are at high risk of fire. Objective: To assess the effect of light availability and soil moisture on the ecophysiological variables of six resprouter species planted under cover of Pinus halepensis Mill. Materials and methods: Arbutus unedo L., Rhamnus alaternus L., Quercus ilex L., Quercus faginea Lam., Fraxinus ornus L. and Acer granatense Boiss. were planted in plots with three pine densities per hectare: HD = 800 to 1 100, MD = 300 to 600 and LD = 100 to 250. The species were also grown in the nursery, trying to maintain the same solar radiation conditions. Photosynthesis (A), stomatal conductance (Gs), photosystem II maximum efficiency (Fv/Fm) and water use efficiency (IWUE) were measured. Results and discussion: Evergreen sclerophyll species (A. unedo, R. alaternus and Q. ilex) showed higher photosynthetic capacity, lower photoinhibition and lower IWUE than deciduous species. In HD, plants showed lower photosynthetic capacity (P Conclusion: The physiological variables of the species were conditioned by shading and changes in water demand produced by tree cover.

The non-native woody species of the flora of Ukraine: Introduction, naturalization and invasion

The process of invasion, naturalization, dispersion and invasive activity of non-native woody species in 5 regional floras, 5 urban floras and over 30 floras of the protected areas is discussed. It has been established that 182 non-native species out of 95 genera and 45 families are currently at different naturalization stages in the spontaneous flora of Ukraine. In terms of life-forms, they may be divided as follows: trees – 41%, shrubs – 35%, trees/shrubs – 15%, lianas – 9%. Most species spread both via seed dispersal and the vegetative way – 56%, using only seed dispersal – 42%, only the vegetative way – 2%. According to the preliminary rating of species-wise invasive activity, 71 species (40%) have naturalized completely, among them 20 invasive species, including 12 transformer species, 29 potentially invasive species, and 22 naturalized species which demonstrate no invasive tendencies. The initial stages of invasion of 111 species are as follows: introduction – 9%, survival – 36%, adaptation of the reproductive sphere – 28%, establishment, formative of local populations – 27%. In terms of dispersion, non-naturalized species are divided as follows: rare – 45%, local – 16%, sporadic – 6%, unique – 12%, spreading under control beyond collections and expositions in botanical gardens and arboretums – 21%. Twelve transformer species, the greatest threat to local diversity, are Acer negundo, Ailanthus altissima, Amorpha fruticosa, Bupleurum fruticosum, Elaeagnus angustifolia, E. rhamnoides, Fraxinus ornus, Parthenocissus quinquefolia, P. vitacea, Robinia pseudoacacia, Rhamnus alaternus, Salix × blanda and 8 invasive proper species: Berberis aquifolia, Colutea orientalis, Daphne laureola, Prunus cerasifera, P. serotina, Quercus ilex, Viburnum tinus, Vitis vinifera. The list of alien species, most widespread in 50 regions of Europe, includes Robinia pseudoacacia (42 regions), Ailanthus altissima (40), Acer negundo (38), Prunus cerasus (34), Quercus rubra (34), Rosa rugosa (34), Prunus domestica (31). The mitigation of the impacts of these species on local biodiversity is possible via the restoration of local native plant communities, land use organization, strict selection of introduced species prior to the introduction, culture of planting management, preventive measures and extending awareness and sharing of information about plant invasions. Therefore, Ukraine’s spontaneous flora is notable for the active process of naturalization of non-native woody species with considerable involvement of invasive alien species. This is the first and preliminary evaluation of the invasive activity of woody species in Ukraine’s flora. The manifestations of the global tendency of increased involvement and invasive activity of alien woody species in domestic flora have been confirmed. These conclusions are also relevant for elaborating the system of preventive, containing and mitigating measures regarding plant invasions in Ukraine.

Allometric biomass equations for young trees of four broadleaved species in Albania

Background: Biomass assessment of young forest stands is important because of their role in the carbon cycling. The aim of this study was to develop biomass equations for young broadleaved species growing in natural conditions in Albania. Methods: Five forest stands were investigated using circular sample plots. Diameter at breast height (DBH) and height (H) from 58 sampled trees ranging in age from 4 to 34 years old of Turkey oak (Quercus cerris L.), sweet chestnut (Castanea sativa Mill.), European hornbeam (Carpinus betulus L.) and manna ash (Fraxinus ornus L.) were measured in situ. Logarithmic regression equations were used and tested for their performance to estimate aboveground and tree-components biomass for each species using DBH, H and their combination DBH2 x H as predictors. Results: We found that DBH was a reliable predictor for estimation of aboveground and components biomass for young trees but the inclusion of height in biomass allometry did not improve the biomass estimation. We observed differences in scale (?0) and exponent (?1) coefficients of biomass models, not only between broadleaved species, but also among tree-components within species. Both coefficients were strongly species-specific and their values reflect differences in biomass stocking rate due to different growth strategies of each species in early development phases. Conclusions: Allometric equations to estimate aboveground and tree-component biomass appeared to be species-specific, meaning that such models are applicable for species growing at sites with similar ecological conditions. From the tree variables used, DBH was the most reliable predictor of aboveground and individual components biomass, whereas height proved to be a promising predictor for stand biomass. These allometric equations developed for young trees will improve the accuracy of current estimates of forest carbon stock in Albania.

Spectroscopic and multivariate data-based method to assess the metabolomic fingerprint of Mediterranean plants.

AbstractIntroductionMost secondary metabolites from plants have a prominent defensive role and repellency against predators and microbial pathogens. These properties largely vary among plant species and offer potential applications as biologically active compounds in medicine as well in agriculture.ObjectivesWe propose a new procedure that combine different spectroscopic techniques and multivariate data analysis to determine the chemical composition and the relative amounts of each metabolites and/or each class of organic compounds. The approach was used for a rapid identification of secondary metabolites from leaf and root of eight Mediterranean plants species.MethodologyThe polar and the apolar extracts of two leaves and roots of each plant were analysed by proton nuclear magnetic resonance (1H‐NMR) and gas chromatography coupled to mass spectrometry (GC–MS), respectively. Multivariate data analysis was used for a faster interpretation of data.ResultsThe metabolic fingerprint of the Mediterranean plants, Acanthus mollis, Dittrichia viscosa, Festuca drymeja, Fraxinus ornus, Fagus sylvatica, Hedera helix, Quercus ilex, and Typha latifolia, showed a complex chemical composition, being specific for each species and plant tissue. Two alditols, mannitol and quercitol, were found in manna ash (Fraxinus ornus) and holm oak (Q. ilex) polar leaf extracts, respectively. The highest levels of aromatic compounds were found in D. viscosa and T. latifolia. Fatty acids were the predominant class of compounds in all apolar extracts under investigation. Triterpene were almost exclusively found in roots, except for holm oak, where they constitute 58% of total extract. Steroids were widespread in leaf extracts.ConclusionThe major advantages of the proposed approach are versatility and rapidity, thus making it suitable for a fast comparison among species and plant tissue types.

The composition of woody plants in the cemeteries of various religious communities in Istanbul-Turkey

Cemeteries harbor and protect the diversity of forest species in urban areas. Inventories of species contribute to a valuable understanding of the indigenous biodiversity within the cemeteries. The goal of this study was to compare the composition of tree and shrub species in cemeteries belonging to the Muslim, Christian and Jewish communities in Istanbul, Turkey. Five cemeteries (Karacaahmet - Muslim; Zincirlikuyu - Muslim; Şişli - Greek Orthodox; Balıklı - Armenian; Hasköy - Jewish) were analyzed to identify and interpret similarities in the density of floral species. The importance of preserving some of these species due to their rarity or threat level was established. Effects of management practices among the selected cemeteries were also encountered. Abies nordmanniana subsp. bornmuelleriana, Viburnum tinus, Fraxinus ornus Cerasus mahaleb, Euonymus latifolius and Liquidambar orientalis were important threatened species. Each of the five cemeteries exhibit different vegetation characteristics and species important to the individual religious traditions. The most widespread species at Karacaahmet were Cupressus spp. (46%) and Pistacia terebinthus (15%). At Zincirlikuyu, tree species were almost identical to those at Karacaahmet and included Cupressus spp. (34%) and Pinus spp. (18%). Tree species identified at Şişli included Cupressus spp. (43%) and Buxus sempervirens (16%). At Balıklı, Rosa spp. (46%) was widespread over the entire site. Cupressus spp. (19%) and Euonymus japonica (15%) were the most widespread tree species at Balıklı. Finally, the most prevalent species at Hasköy were Ligustrum lucidium (35%), and Euonymus japonica (18%). The Karacaahmet and Zincirlikuyu exhibited the diversity of plant species. They were followed by Balıklı, Şişli, and Hasköy, respectively. The density of plant species was highest at Zincirlikuyu, followed by Karacaahmet, Hasköy, Şişli, and Balıklı. A centralized system of management that recognizes and respects the differences in religious beliefs, cultures, and site conditions could be beneficial for the Istanbul cemeteries which are natural and cultural heritage bridges from the past to the future.

Effect of a mixture of botanicals extracts plus mannitol on hydration and bloating sensation. An open label study in women with high extra cellular water

The aim of the study is to evaluate the effectiveness of of 4 and 8 week supplementation with highly standardized formula with Fraxinus ornus L., plus Ananas comosus L., concentrated juice, Betula pendula R., Equisetum arvense L., Urtica dioica L. and Pilosella officinarum L. Vail dry extract, on the state of hydration and bloating sensation in subjects with high and moderate extra cellular water (ECW). 19 women (mean age 35 yr and Body Mass Index 22.82 kg\\m2) with Extra Cellular Water over 45%completed the study and their data were analysed at baseline, at 30 and 60 days. Bio-impedance, SF36 and anthropometric parameters were assessed. The ECW decreased of −1.97% (at 30 days) and −2.30% (60 days) (p < 0.01). Also fat mass decreased of −1.58% (at 30 days) and −2.21% (60 days) (p = 0.057). An improvement of free fat mass was assessed (p < 0.05) but not on bloating sensation questionnaire at 60 days (p = 0.422).

Influence of the early bacterial biofilms developed on vats made with seven wood types on PDO Vastedda della valle del Belìce cheese characteristics

Early vat bacterial biofilms developed spontaneously through contact with whey have been characterized on seven wood types (Castanea sativa Miller, Cedrus libani, A. Rich., Prunus avium L., Fraxinus ornus L., Juglans regia L., Pinus nigra J.F. Arnold and Populus nigra L.). The present study aimed to evaluate the influence of these biofilms on the microbiological, chemical, physical and sensory characteristics of PDO Vastedda della valle del Belìce (VdB) cheese, processed traditionally from raw ewe's milk using wooden tools. To this purpose, the experimental cheeses after 15 d of refrigerated storage were examined. Lactic acid bacteria (LAB) populations dominated the microbial community of all samples. The species more frequently identified were Lactococcus lactis among starter LAB and Lactobacillus paracasei, Lactobacillus rhamnosus, Lactobacillus fermentum and Pediococcus pentosaceus among non starter LAB. Culture-independent analysis of microbiota diversity was performed by MiSeq Illumina that identified Streptococcus as major group followed by members of Enterobacteriaceae family, Lactococcus and Lactobacillus. Generally, the seven tree species did not negatively affect the physicochemical composition of VdB cheeses. Chestnut (both Sicilian and Calabrian) vats produced cheeses with significant lower hue angle (a*/b*) than other wood types. Among chemical parameters, significant variations were registered for aw, primary and secondary lipid oxidation state (significantly lower for the VdB cheeses produced with poplar wood), and volatile organic compounds (VOCs). The significant differences detected among the VOCs emitted from cheeses were not perceived by the panelists who recognized all cheeses from the different trials as similar. This study confirmed the suitability of cedar, cherry, ash, walnut, black pine and poplar as alternative woods to chestnut for the production of the wooden vats employed in cheese making for the Sicilian traditional dairy productions.

The Endophytic Mycobiome of European Ash and Sycamore Maple Leaves - Geographic Patterns, Host Specificity and Influence of Ash Dieback.

The European ash (Fraxinus excelsior) is threatened by the introduced ascomycete Hymenoscyphus fraxineus, the causal agent of ash dieback. Endophytic fungi are known to modulate their host’s resistance against pathogens. To understand possible consequences of ash dieback on the endophytic mycobiome, F. excelsior leaves were collected in naturally regenerated forests and the fungal communities analyzed by classic culture and Illumina amplicon sequencing using a newly developed and validated fungal-specific primer. Collections were done in the area infested by ash dieback north of the Alps, and in the disease free area on the south side. Sycamore maple (Acer pseudoplatanus) was additionally collected, as well as the flowering ash (F. ornus), which occurs naturally in the south and shows tolerance to ash dieback. Both cultivation and amplicon sequencing revealed characteristic endophytic fungal communities dominated by several strictly host specific Venturia species. On A. pseudoplatanus, a hitherto undescribed Venturia species was identified. Due to its dominance on F. excelsior, V. fraxini is unlikely to go extinct in case of reduced host densities. A majority of species was not strictly host specific and is therefore likely less affected by ash dieback in the future. Still, shifts in community structure and loss of genetic diversity cannot be excluded. The potentially endangered endophyte Hymenoscyphus albidus was rarely found. In addition to host specificity, species with preferences for leaf laminae or petioles were found. We also detected considerable geographical variation between sampling sites and clear differences between the two sides of the Alps for endophytes of F. excelsior, but not A. pseudoplatanus. Since sycamore maple is not affected by an epidemic, this could point toward an influence of ash dieback on ash communities, although firm conclusions are not possible because of host preferences and climatic differences. Furthermore, the mycobiota of F. excelsior trees with or without dieback symptoms were compared, but no clear differences were detected. Besides methodical refinement, our study provides comprehensive data on the ash mycobiome that we expect to be subject to changes caused by an emerging disease of the host tree.

Similarities and differences in the balances between leaf, xylem and phloem structures in Fraxinus ornus along an environmental gradient.

The plant carbon balance depends on the coordination between photosynthesis and the long-distance transport of water and sugars. How plants modify the allocation to the different structures affecting this coordination under different environmental conditions has been poorly investigated. In this study, we evaluated the effect of soil water availability on the allocation to leaf, xylem and phloem structures in Fraxinus ornus L. We selected small individuals of F. ornus (height ~2 m) from sites contrasting in soil water availability (wet vs dry). We measured how the leaf (LM) and stem + branch biomass (SBM) are cumulated along the stem. Moreover, we assessed the axial variation in xylem (XA) and phloem tissue area (PA), and in lumen area of xylem vessels (CAxy) and phloem sieve elements (CAph). We found a higher ratio of LM:SBM in the trees growing under drier conditions. The long-distance transport tissues of xylem and phloem followed axial patterns with scaling exponents (b) independent of site conditions. PA scaled isometrically with XA (b ~ 1). While CAxy was only marginally higher at the wet sites, CAph was significantly higher at the drier sites. Our results showed that under reduced soil water availability, F. ornus trees allocate relatively more to the leaf biomass and produce more conductive phloem, which is likely to compensate for the drought-related hydraulic limitations to the leaf gas exchanges and the phloem sap viscosity.

Less safety for more efficiency: water relations and hydraulics of the invasive tree Ailanthus altissima (Mill.) Swingle compared with native Fraxinus ornus L.

Invasion of natural habitats by alien trees is a threat to forest conservation. Our understanding of fundamental ecophysiological mechanisms promoting plant invasions is still limited, and hydraulic and water relation traits have been only seldom included in studies comparing native and invasive trees. We compared several leaf and wood functional and mechanistic traits in co-occurring Ailanthus altissima (Mill.) Swingle (Aa) and Fraxinus ornus L. (Fo). Aa is one of the most invasive woody species in Europe and North America, currently outcompeting several native trees including Fo. We aimed at quantifying inter-specific differences in terms of: (i) performance in resource use and acquisition; (ii) hydraulic efficiency and safety; (iii) carbon costs associated to leaf and wood construction; and (iv) plasticity of functional and mechanistic traits in response to light availability. Traits related to leaf and wood construction and drought resistance significantly differed between the two species. Fo sustained higher structural costs than Aa, but was more resistant to drought. The lower resistance to drought stress of Aa was counterbalanced by higher water transport efficiency, but possibly required mechanisms of resilience to drought-induced hydraulic damage. Larger phenotypic plasticity of Aa in response to light availability could also promote the invasive potential of the species.

Evaluating the impact of Hymenoscyphus fraxineus in Trentino (Alps, Northern Italy): first investigations

Abstract: The spread of Hymenoscyphus fraxineus has been causing great concern regarding the survival of European ash (Fraxinus excelsior) throughout Europe since the 1990s. The disease was first recorded in Trentino (southern Alps, Italy) in 2012 and has spread throughout the mountain landscape, where ash trees are scattered in small and isolated stands in different valleys. The status of the disease was checked by monitoring the damage to natural regeneration and adult trees in 90 sites spread over the whole region. The survey confirmed the complete colonization by the pathogen of the whole investigated area, with high levels of damage to both young and adult ash trees. Regeneration (both seedlings and saplings) was observed to be affected by the fungus in 88 plots out of 90. Out of 4486 examined young European ashes, 2261 (50.4%) were affected and 789 (17.6%) were already dead. Ten of the 384 assayed flowering ashes (Fraxinus ornus) showed symptoms on branches and apical stems, similar to those observed for European ash. Isolation and molecular analysis proved the presence of the fungus on both symptomatic European and flowering ashes. The examined 386 adult trees showed different levels of damage, sometimes reaching more than 75% of the crown. Some individual trees (42) growing close to severely damaged trees appeared fully healthy, which suggests the possible existence of some resistant/tolerant individuals in the examined populations.

Functional indicators of response mechanisms to nitrogen deposition, ozone, and their interaction in two Mediterranean tree species.

The effects of nitrogen (N) deposition, tropospheric ozone (O3) and their interaction were investigated in two Mediterranean tree species, Fraxinus ornus L. (deciduous) and Quercus ilex L. (evergreen), having different leaf habits and resource use strategies. An experiment was conducted under controlled condition to analyse how nitrogen deposition affects the ecophysiological and biochemical traits, and to explore how the nitrogen-induced changes influence the response to O3. For both factors we selected realistic exposures (20 kg N ha-1 yr-1 and 80 ppb h for nitrogen and O3, respectively), in order to elucidate the mechanisms implemented by the plants. Nitrogen addition resulted in higher nitrogen concentration at the leaf level in F. ornus, whereas a slight increase was detected in Q. ilex. Nitrogen enhanced the maximum rate of assimilation and ribulose 1,5-bisphosphate regeneration in both species, whereas it influenced the light harvesting complex only in the deciduous F. ornus that was also affected by O3 (reduced assimilation rate and accelerated senescence-related processes). Conversely, Q. ilex developed an avoidance mechanism to cope with O3, confirming a substantial O3 tolerance of this species. Nitrogen seemed to ameliorate the harmful effects of O3 in F. ornus: the hypothesized mechanism of action involved the production of nitrogen oxide as the first antioxidant barrier, followed by enzymatic antioxidant response. In Q. ilex, the interaction was not detected on gas exchange and photosystem functionality; however, in this species, nitrogen might stimulate an alternative antioxidant response such as the emission of volatile organic compounds. Antioxidant enzyme activity was lower in plants treated with both O3 and nitrogen even though reactive oxygen species production did not differ between the treatments.

Effects of the Antiozonant Ethylenediurea (EDU) on Fraxinus ornus L.: The Role of Drought

Ethylenediurea (EDU) is a synthetic chemical known to protect plants from the phytotoxic effects of tropospheric ozone (O3). Although many studies have proposed the use of EDU for studying the O3 effects under field conditions, its mechanism of action is not fully understood, and it is unclear whether it exerts a specific antiozonant action, or if it may also interact with other oxidative stresses. The aim of this work was to evaluate the effect of EDU on forest species in a Mediterranean environment where, during summer, vegetation is exposed to multiple oxidative stresses, such as O3 and drought. The experiment was conducted on Fraxinus ornus L. (Manna ash) plants growing in six mesocosms, three maintained under full irrigation, while the other three were subjected to drought for 84 days. In each mesocosm, three plants were sprayed every 15 days with 450 ppm EDU. Gas exchange and chlorophyll “a” fluorescence measurements carried out through the experimental period highlighted that EDU did not affect stomatal conductance and had an ameliorative effect on the functionality of drought-stressed plants, thus suggesting that it may act as a generic antioxidant. The implications of these findings for the applicability of EDU in field studies are discussed.