Search

Pea (Pisum sativum) is one of the most popular legume crops used in agriculture. Because of the high demand and relatively reasonable price, Lithuania has increased the cultivation of this crop and invested in the research of new effective breeding lines in the last years. Rhizobial inoculants contribute to increasing yield in legumes through N2 fixation. Therefore, the objective of this work was to identify rhizobial strains able to increase the activity of two pea breeding lines (‘DS 3637–2’ and ‘DS 3795–3’) known for high productivity, resistance to biotic and abiotic stresses, and competitiveness in respect to weeds. Six rhizobial strains isolated from pea plants were identified as members of the Rhizobium leguminosarum group and phenotypically characterized in depth by Phenotype Microarray (PM). Phenotypic differences observed were linked to their phylogeny. Then, strains were tested for their ability to stimulate the growth of the breeding lines ‘DS 3637–2’ and ‘DS 3795–3’. Reference strain Rhizobium anhuiense Z1 and Rhizobium leguminosarum sv. viciae 14ZE showed the best symbiotic performances with breeding lines ‘DS 3637–2’ and ‘DS 3795–3’, respectively. Based on the obtained results, R. leguminosarum sv. viciae strain 14ZE appears to be a new effective inoculant of peas.

Replicate common gardens of Italian and Greek provenances of Quercus ilex, Q. pubescens, and Q. frainetto seedlings were established in 2017 in Italy, Greece, and Germany (here: also Q. robur) to assess their potential for plantations for future climate scenarios. The JIP-test was applied on saplings (2016) and in the summers of 2017-2019 to assess the efficiency of the photosynthetic apparatus. Seedlings from the nurseries differed in the tested JIP parameters from older plants in the field. Further, considerable inter-annual and between-sites variability of the parameters occurred. Q. pubescens revealed the most stable behavior across time and site, with the Greek provenance usually showing higher values of performance index and the probability of electron transport beyond QA- than the Italian provenance. In the German sites, Greek Q. pubescens revealed higher values of most of the tested JIP parameters than the local species, Q. robur.

One of the most fundamental questions in ecology is how many species inhabit the Earth. However, due to massive logistical and financial challenges and taxonomic difficulties connected to the species concept definition, the global numbers of species, including those of important and well-studied life forms such as trees, still remain largely unknown. Here, based on global ground-sourced data, we estimate the total tree species richness at global, continental, and biome levels. Our results indicate that there are ∼73,000 tree species globally, among which ∼9,000 tree species are yet to be discovered. Roughly 40% of undiscovered tree species are in South America. Moreover, almost one-third of all tree species to be discovered may be rare, with very low populations and limited spatial distribution (likely in remote tropical lowlands and mountains). These findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species and thus, global tree richness., Proceedings of the National Academy of Sciences of the United States of America, 119 (6), ISSN:0027-8424, ISSN:1091-6490

Climate change imposes severe stress on European forests, with forest degradation already visible in several parts of Europe. Thus adaptation of forestry applications in Mediterranean areas and central Europe is necessary. Proactive forestry management may include the planting of Mediterranean oak species in oak-bearing Central European regions. Five replicate common gardens of Greek and Italian provenances of Quercus ilex, Q. pubescens and Q. frainetto seedlings (210 each per plantation) were established in Central Italy, NE Greece (two) and Southern Germany (two, including Q. robur) to assess their performance under different climate conditions. Climate and soil data of the plantation sites are given and seedling establishment was monitored for survival and morphological parameters. After 3 years (2019) survival rates were satisfactory in the German and Italian sites, whereas the Greek sites exerted extremely harsh conditions for the seedlings, including extreme frost and drought events. In Germany, seedlings suffered extreme heat and drought periods in 2018 and 2019 but responded well. Provenances were ranked for each country for their performance after plantation. In Greece and Italy, Q. pubescens was the best performing species. In Germany, Q. pubescens and Q. robur performed best. We suggest that Greek or Italian provenances of Q. pubescens may be effectively used for future forestation purposes in Central Europe. For the establishment of Quercus plantations in Northern Greece, irrigation appears to be a crucial factor in seedling establishment.

The definition of stress comes from the physical sciences and refers to the ability of a force applied to a material to induce a deformation (strain). Unlike materials, living organisms and biological systems react to stress with responses to prevent or repair the damage. Plants exposed to stressful conditions move from an optimal (non-stressed) to sub-optimal state, until they reach a new equilibrium with the changed environmental conditions, through physiological, biochemical, and genetic pathways to cope with the new environmental conditions. Multiple fluctuating environmental pressures often act simultaneously, then the effects of individual stresses cannot be isolated. In natural ecosystems, plants, and plant communities, naturally adapted to harsh environments, are in equilibrium with their environment. This equilibrium can be considered as “optimal” albeit in relative terms (i.e., for a specific genotype at a specific site). The mechanisms of acclimatization and adaptation are important especially in trees, which are sessile long-living organisms, unable to escape from the worsening of the environmental conditions. Rapid climate change, with severe drought and heat waves, can have different effects in relation to their level of equilibrium before the impact (starting point). The new equilibrium can be defined in terms of fitness (capacity of individuals to grow and reproduce) and resilience (capacity to cope to stress and restore the condition prior to the disturbing factor). Field studies suggest that the photosynthetic efficiency can be preserved or restored in short time after the stress event, but resilience (measured in terms of dynamic of non-structural carbohydrates at tree level) may be more severely affected. The conservation and management activities of natural resources require monitoring the stress conditions of vegetation and predicting the possible changes in species composition and structure of communities and ecosystems. This is desirable to maintain and optimise the ecosystem services in a new environmental and future climate scenario.

Forest health and multifunctionality are threatened by global challenges such as climate change. Forest health is currently assessed within the pan-European ICP Forests (International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests) programme through the evaluation of tree crown conditions (defoliation). This paper analyses the results of a 24-year assessment carried out in Italy on 253 permanent plots distributed across the whole forested area. The results evidenced a substantial stability of crown conditions at the national level, according to the usual defoliation thresholds Defoliation &gt, 25% and Defoliation &gt, 60%, albeit with species-specific patterns. Within this apparent temporal stability, an increased fraction of extremely defoliated and dead trees was observed. Extreme defoliation mostly occurred in years with severe summer drought, whereas mortality was higher in the years after the drought. The results for singular species evidenced critical conditions for Castanea sativa Mill. and Pinus species, whereas Quercus species showed a progressive decrease in defoliation. Deciduous species, such as Fagus sylvatica L., Ostrya carpinifolia Scop. and Quercus pubescens Willd. suffer the loss of leaves in dry years as a strategy to limit water loss by transpiration but recover their crown in the following years. The recurrence of extreme heat waves and drought from the beginning of the XXI century may increase the vulnerability of forests, and increased tree mortality can be expected in the future.

Climate change and extreme drought and heat events impact the Mediterranean evergreen sclerophyllous vegetation in South Europe, especially in Iberian and Italian peninsula, where widespread crown defoliation and dieback have been observed since the 90s of the XX century. Field observations and long-term experiments showed different sensitivity of the various woody species, Quercus ilex and Arbutus unedo being prone to drought, whereas Phillyrea latifolia and Pistacia lentiscus appeared to be resistant. The present review aims at exploring the phylogenetic and evolutionary basis of the resistance (or susceptibility) to drought of Mediterranean vegetation and its possible mechanisms of resilience. The main findings are summarized as follows: (1) Mediterranean regions in the world are refuge areas for several plant evolutive lineages and migratory routes. Evergreen sclerophyllous species, currently presented in Mediterranean basin, evolved under different climatic conditions; (2) the evergreen habitus represents an adaptation to mild drought conditions. Deciduous (specially summer deciduous) species are better performing under severe drought and low air relative humidity than evergreen species; (3) severe drought events acts selectively by favouring the species evolved in the Quaternary era and those originated in drier regions; (4) the evergreen trees and shrubs are resilient to the severe drought events and can restore the pre-event condition by resprouting from dormant buds in the cambium tissue. This ability is related to the non-structural carbohydrate content in the parenchyma-rays in woody stems. The amount and availability of these strategic reserve can be compromised by frequent drought events; (5) plant seed regeneration can be affected by drought and seedling establishment may be limited by soil dryness and microenvironment conditions; (6) the role of phenotypic plasticity of the species and epigenetic responses in Mediterranean-type ecosystems, although discussed in few papers, is still poorly known. We hypothesize that instead of latitudinal (South to North) or altitudinal (lowland to upland) plant migrations, Mediterranean forest ecosystems may respond to climate change by modulating their species composition and community structure with genetic resources (i.e., taxonomic diversity) already present in loco. Changes in vegetation assemblages and community structure may lead changes in ecological and landscape ecosystem values, with changes in related ecosystem services. A redefinition of management criteria of natural resources and a pro-active silviculture to make forest ecosystems more resilient are required.

Agricultural production is predicted to be adversely affected by an increase in drought and heatwaves. Drought and heat damage cellular membranes, such as the thylakoid membranes where photosystem II occurs (PSII). We investigated the chlorophyll fluorescence (ChlF) of PSII, photosynthetic pigments, membrane damage, and the activity of protective antioxidants in drought-tolerant and -sensitive varieties of C3 sunflower and C4 maize grown at 20/25 and 30/35 &deg, C. Drought-tolerant varieties retained PSII electron transport at lower levels of water availability at both temperatures. Drought and heat stress, in combination and isolation, had a more pronounced effect on the ChlF of the C3 species. For phenotyping, the maximum fluorescence was the most effective ChlF measure in characterizing varietal variation in the response of both species to drought and heat. The drought-tolerant sunflower and maize showed lower lipid peroxidation under drought and heat stress. The greater retention of PSII function in the drought-tolerant sunflower and maize at higher temperatures was associated with an increase in the activities of antioxidants (glutathione reductase, superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase), whereas antioxidant activity declined in the drought-sensitive varieties. Antioxidant activity should play a key role in the development of drought- and heat-tolerant crops for future food security.

Mast seeding, the synchronised occurrence of large amounts of fruits and seeds at irregular intervals, is a reproductive strategy in many wind-pollinated species. Although a series of studies have investigated mast year (MY) patterns in European forest tree species at the regional scale, there are few recent evaluations at a European scale on the impact of weather variables (weather cues) and resource dynamics on mast behaviour. Thus the main objective of this study is to investigate the impact of specific weather conditions, as environmental drivers for MYs, on resources in Fagus sylvatica L., Quercus petraea ( Matt.) Liebl. , Quercus robur L., Picea abies (L.) Karst . and Pinus sylvestris L. at a European level and to explore the robustness of the relationships in smaller regions within Europe. Data on seed production originating from the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) were analysed. Three beta regression models were applied to investigate the impact of seasonal weather variables on MY occurrence, as well as the influence of fruiting intensity levels in the years prior to MYs. Resource dynamics are analysed at three different spatial scales (continent, countries and ecoregions). At a European scale, important weather cues for beech MYs were a cold and wet summer two years before a MY, a dry and warm summer one year before a MY and a warm spring in the MY. For spruce, a cold and dry summer two years prior to a MY and a warm and dry summer in the year before the MY showed the strongest associations with the MY. For oak, high spring temperature in the MY was the most important weather cue. For beech and spruce, and to some extent also for oak species, the best fitting models at European scale were well reflected by those found at smaller scales. For pine, best fitting models were highly diverse concerning weather cues. Fruiting levels were high in all species two years before the MY and also high one year before the MY in the oak species and in pine. In beech, fruiting levels one year before the MY were not important and in spruce, they were inconsistent depending on the region. As a consequence, evidence of resource depletion could only be seen in some regions for spruce.

Production of wood charcoal is a traditional form of forest use that lasted for millennia in most temperate regions, vanishing only some decades ago in the Mediterranean countries. Here, the abandoned charcoal hearths form a network of microhabitats with peculiar vegetation and soil conditions. Previous observational studies showed that establishment of woody species at these sites is severely hindered for unknown reasons. To test the effects of charcoal hearth soil on tree growth we used a common garden experiment with three major Euro-Mediterranean forest trees with different traits and ecology, one evergreen (Quercus ilex, holm oak) and two deciduous (Fagus sylvatica, beech, and Quercus cerris, Turkey oak). These were sown on control and charcoal-enriched soil collected in forest hearths abandoned since decades. Seed germination, seedling growth, photosynthetic efficiency and mortality were measured over a period of two years. Some responses were species-specific, while others were possibly associated to key traits such as evergreen vs. deciduous habit. Although charcoal soil effects were mainly positive on growth rate (height increase), they were mostly negative on germination of beech seeds, survival of holm oak seedlings, and photosynthetic efficiency. Although total biomass was not significantly affected, the root:shoot ratio was increased as a possible effect of physiological drought on hearth soil. These results support field-based evidence that the long persistence of charcoal remains in the soil may be not a favourable condition for forest regeneration. Management implications concern the use of biochar practices to promote forest restoration, which should be further tested on a wide range of species in different life-stages before applications in the field, also considering its long-term consequences.

This study presents a reanalysis of ozone (O3) exposure experiments performed on deciduous broadleaf oak species in the Mediterranean region and a proposal of critical levels to improve the O3 risk assessment in this area for these widely distributed forest species. Two experiments performed in Spain and Italy were considered, and the following 3 oak species were studied: Quercus pyrenaica, Q. faginea and Q. robur. All the experiments were performed with irrigated potted seedlings growing in Open-Top Chambers exposed to different O3 levels (with charcoal-filtered air as the control treatment) for two consecutive growing seasons. The Phytotoxic Ozone Dose above an instantaneous threshold of 1 nmol O3 m−2 s−1 (POD1) was calculated by applying a Jarvis type model for the estimation of the stomatal conductance (gs), and by adopting a big-leaf resistive scheme to account for the O3 deposition on the vegetation. Two parameterisations were used for the gs multiplicative model: one species-specific based on the “local” gs measurements performed during each experiment, and the other “generic” based on the “Deciduous Mediterranean broadleaf” parameterisation described in the Manual on Methodologies and Criteria for Mapping Critical Loads and Levels and Air Pollution Effects, Risks and Trends of the UN/ECE (CLRTAP, 2015). The two different parameterisations were used to derive dose-response functions and ozone critical levels for the biomass loss of the deciduous oak species. The dose-response functions for roots and total biomass were statistically significant, with both the parameterisations tested (p

A chlorophyll fluorescence (ChlF) assessment was carried out on oak seedlings (Quercus ilex L., Quercus pubescens Willd., Quercus frainetto Ten.) of Italian and Greek provenance, during the years 2017 and 2018, in a common garden in central Italy planted in 2017. This trial aimed to test the relative performances of the oak species in the perspective of assisted migration as part of the actions for the adaptation of forests to climate change. The assessment of the photosynthetic performance of the tree species included the analysis of the prompt chlorophyll fluorescence (PF) transient and the modulated reflection (MR) at 820 nm, leaf chlorophyll content, leaf gas exchange (net photosynthesis, stomatal conductance), plant growth (i.e., height) and mortality rate after 2 years from the beginning of the experiment. The assessment of the performance of the three oak species was carried out ‘in vivo’. Plants were generated from seeds and exposed to several environmental factors, including changing seasonal temperature, water availability, and soil biological and physical functionality. The results of PF indicate a stable functionality of the photosynthetic system PSII (expressed as FV/FM) across species and provenances and a decline in photochemistry functionality at the I–P phase (ΔVIP) in Q. frainetto, thus indicating a decline of the content of PSI in this species. This result was confirmed by the findings of MR analysis, with the speed of reduction and subsequent oxidation of PSI (VRED and VOX) strongly correlated to the amplitude of ΔVIP. The photosynthetic rates (net photosynthesis, PN) and growth were correlated with the parameters associated with PSI content and function, rather than those related to PSII. The low performance of Q. frainetto in the common garden seems to be related to early foliar senescence with the depletion of nitrogen, due to suboptimal climatic and edaphic conditions. Chlorophyll fluorescence allowed discrimination of populations of oak species and individuation of the less (or/and best) suitable species for future forest ecology and management purposes.

The purpose of this study was to analyze the effects of altitude, the position of the trees along a gradient of canopy cover, and the orientation of their crown on leaf traits of 18 deciduous woody species belonging to 10 families in the Fandoglo forest region in Ardabil, North West of Iran. We measured eight leaf traits (leaf width, length, area, thickness, water content, leaf mass per area, specific leaf area, and dry matter concentration) of trees sampled at sites subjected to different light regimes (forest edge, forest understory, and isolated trees). All traits were measured on more than 3600 leaves from 90 trees sampled in two altitudinal ranges (low: 1300-1500 m a.s.l.; high: 1500-1700 m a.s.l.). A two-way ANOVA and t-test for independent samples were applied to test for differences in leaf traits between different altitudes and degree of canopy cover. The results confirmed that species’ leaf traits were more strongly correlated with the altitude and canopy cover rather than the orientation of the crown. No relationship between leaf traits and crown orientation was detected. All leaf traits had significantly higher values at low than at high elevation, indicating that environmental factors such as atmospheric CO2 concentration, temperature, light, irradiance, and wind deeply impact on foliar morphology and function; however, water content and specific leaf area showed an opposite trend. Also, species with different positions along the gradient of canopy cover could have different responses to elevation. Our results indicate that the variation of functional (morphological and physiological) traits in different tree species are affected by altitude and light regime. This might provide a theoretical basis for afforestation and forest management activities in the Fandoghlo forest region.

Plant functional diversity (FD) is an important component of biodiversity that characterizes the variability of functional traits within a community, landscape, or even large spatial scales. It can influence ecosystem processes and stability. Hence, it is important to understand how and why FD varies within and between ecosystems, along resources availability gradients and climate gradients, and across vegetation successional stages. Usually, FD is assessed through labor-intensive field measurements, while assessing FD from space may provide a way to monitor global FD changes in a consistent, time and resource efficient way. The potential of operational satellites for inferring FD, however, remains to be demonstrated. Here we studied the relationships between FD and spectral reflectance measurements taken by ESA's Sentinel-2 satellite over 117 field plots located in 6 European countries, with 46 plots having in-situ sampled leaf traits and the other 71 using traits from the TRY database. These field plots represent major European forest types, from boreal forests in Finland to Mediterranean mixed forests in Spain. Based on in-situ data collected in 2013 we computed functional dispersion (FDis), a measure of FD, using foliar and whole-plant traits of known ecological significance. These included five foliar traits: leaf nitrogen concentration (N%), leaf carbon concentration (%C), specific leaf area (SLA), leaf dry matter content (LDMC), leaf area (LA). In addition they included three whole-plant traits: tree height (H), crown cross-sectional area (CCSA), and diameter-at-breast-height (DBH). We applied partial least squares regression using Sentinel-2 surface reflectance measured in 2015 as predictive variables to model in-situ FDis measurements. We predicted, in cross-validation, 55% of the variation in the observed FDis. We also showed that the red-edge, near infrared and shortwave infrared regions of Sentinel-2 are more important than the visible region for predicting FDis. An initial 30-m resolution mapping of FDis revealed large local FDis variation within each forest type. The novelty of this study is the effective integration of spaceborne and in-situ measurements at a continental scale, and hence represents a key step towards achieving rapid global biodiversity monitoring schemes., This work was primarily supported by an iDiv-Flexpool project “Observing effects of biodiversity on ecosystem functioning across time, space, and wavelength: oBEF-Across” and a European Union H2020 project “Detecting changes in essential ecosystem and biodiversity properties - towards a Biosphere Atmosphere Change Index: BACI” (grant agreement number: 640176). The data from FunDivEUROPE network was collected with the financial support from the European Union Seventh Framework Programme (FP7/2007-2013) (grant agreement number: 265171). Remeasurements across all FunDivEUROPE plots were financed by EU H2020 project Soil4Europe (Bioidversa 2017-2019). We thank Prof. Dr. Michael Scherer-Lorenzen and Prof. Dr. Kris Verheyen from FunDivEUROPE network for their generous help with field data during the paper revision. DEPM and MM and MDM also acknowledge the support of the Trustee European Commission project no H2020-MSCA-ITN-2016 – 721995. The free use of Sentinel-2 data is enabled by ESA's Copernicus Open Access Hub. The in-situ plant traits data collected over Finnish, Romanian, and Spanish sites were supported by a Marie-Curie Fellowship (DIVERFOR, FP7-PEOPLE-2011-IEF. No. 302445) to R. Benavides. The free access of plant trait data was supported by the TRY initiative (http://www.try-db.org)

Microcystis is a genus of unicellular blue-green algae that is toxic and can be troublesome in freshwater, especially where organic material is abundant. The aim of this work was to analyse photosystem I (PSI) and photosystem II (PSII) photochemistry of Microcystis spp. colonies under salt stress by the use of comprehensive chlorophyll a fluorescence signals measurements (prompt, delayed and modulated 820 nm reflection- MR 820). The cyanobacteria samples were taken from a natural aquatic environment. The following salt solutions were applied with 10 days intervals: 0.00 (control), 0.05, 0.10, 0.20, 0.40, 0.80, and 1.00 M. Data was collected three times (10, 20 and 30 days after treatment), prior to increasing the salt concentration in the solution. We found that the salt stress inhibited electron transfer from the PQ pool to PSI (P700+) and the inhibition of reoxidation of the plastoquinone molecule tightly bound to PSII (QA−). An inhibition of quantum yields of photoinduced electron transport in PSII reaction center to QA and a reduction of the fast phase of photoinduced kinetics of the MR was also noted under this stress. We recommend the combined analyses of the prompt and delayed chlorophyll fluorescence along with MR820 to be used as a novel qualitative method for studying photosynthetic machinery reactions not only in higher plants, but also in cyanobacteria.

Summary Different tree species influence litter decomposition directly through species-specific litter traits, and indirectly through distinct modifications of the local decomposition environment. Whether these indirect effects on decomposition are influenced by tree species diversity is presently not clear. We addressed this question by studying the decomposition of two common substrates, cellulose paper and wood sticks, in a total of 209 forest stands of varying tree species diversity across six major forest types at the scale of Europe. Tree species richness showed a weak but positive correlation with the decomposition of cellulose but not with that of wood. Surprisingly, macroclimate had only a minor effect on cellulose decomposition and no effect on wood decomposition despite the wide range in climatic conditions among sites from Mediterranean to boreal forests. Instead, forest canopy density and stand-specific litter traits affected the decomposition of both substrates, with a particularly clear negative effect of the proportion of evergreen tree litter. Our study suggests that species richness and composition of tree canopies modify decomposition indirectly through changes in microenvironmental conditions. These canopy-induced differences in the local decomposition environment control decomposition to a greater extent than continental-scale differences in macroclimatic conditions.

Tibouchina pulchra (Cham.) Cogn., a pioneer tree species commonly found in the Atlantic Rain Forest in southeast Brazil, proved to be a promising biosensor species for indicating the potential effects of air pollution on this type of forest. This study aimed to investigate whether the present levels of nitrogen oxides, sulfur oxides, ozone and particulate matter in industrial and urban areas in the Cubatao region induce structural and ultrastructural changes in this species, to explore the synergy between air pollutants and the effects of other environmental stressors as contributors to microscopic symptoms and to verify whether these changes are seasonally dependent. The field study consisted of exposing potted saplings of T. pulchra in three sites around the petrochemical industry (industrial area), in downtown Cubatao (urban area) and in a site far from the industrial emissions (reference area). An experimental study using open top chambers (OTC) with filtered air and non-filtered air was also carried out to confirm the field results. Four exposure periods of 12 weeks were conducted during the field and the OTC experiments, covering wet and dry periods. The effects were more pronounced in plants exposed in the industrial areas during the dry period, which were confirmed by OTC experiments. Crystal density variations were linearly explained by decreases in NO 2 , SO 2 and the sum of all hourly concentrations of ozone (SUM00), as well as increases in PM 10 , relative humidity and rainfall. Variations in lipid peroxidation correlated positively with air temperature and SUM00. Tannins and starch grains decreased. Collapsed and sinuous cell walls, dense cytoplasm, invagination of plasma membranes and vacuome were the main effects observed at the structural level. Occurrence of pectic warts, alterations in chloroplasts and numerous vesicles close to the cell walls were the main ultrastructural effects detected. These results confirmed that pollutants and environmental variables acted synergistically to induce oxidative stress in this species, enhancing our understanding of the bioindicator potential of T. pulchra for monitoring complex mixtures of air pollutants in the tropics.

Average nitrogen (N) deposition across Europe has declined since the 1990s. This resulted in decreased N inputs to forest ecosystems especially in Central and Western Europe where deposition levels are highest. While the impact of atmospheric N deposition on forests has been receiving much attention for decades, ecosystem responses to the decline in N inputs received less attention. Here, we review observational studies reporting on trends in a number of indicators: soil acidification and eutrophication, understory vegetation, tree nutrition (foliar element concentrations) as well as tree vitality and growth in response to decreasing N deposition across Europe. Ecosystem responses varied with limited decrease in soil solution nitrate concentrations and potentially also foliar N concentrations. There was no large-scale response in understory vegetation, tree growth, or vitality. Experimental studies support the observation of a more distinct reaction of soil solution and foliar element concentrations to changes in N supply compared to the three other parameters. According to the most likely scenarios, further decrease of N deposition will be limited. We hypothesize that this expected decline will not cause major responses of the parameters analysed in this study. Instead, future changes might be more strongly controlled by the development of N pools accumulated within forest soils, affected by climate change and forest management. We find limited indication for response of Europe's forests to declining N deposition. Reactions have been reported for soil solution NO3 − and potentially foliar N concentrations but not for other indicators.

Tree diversity is found to enhance ecosystem functions in forests and increase the resistance and resilience of trees subjected to environmental stress, including climate change. This effect, however, can be different depending on tree species assemblages and ecological contexts. The pan-European programme for monitoring forest health (ICP Forests) considers crown defoliation as an indicator of tree vitality. Only a few studies have analysed the role of tree diversity in crown defoliation, with contrasting results. This paper analyses the relationships between defoliation and forest diversity in a country (Italy) characterised by heterogeneous bioclimatic and edaphic characteristics (from Mediterranean to Alpine) and with a wide range of forest tree species and functional groups. National-scale results show that defoliation increased in more diverse forest stands. This result can be explained by the fact that the tree mixtures reflect varying ecological conditions in heterogeneous environments. The most relevant factors that explain tree defoliation at the national level, investigated through random forest analysis, were the geographic position, tree species identity and forest stand age and structure. Cluster analysis was applied to identify homogeneous groups of plots based on their ecological and vegetation features. Four clusters were selected. Within each homogeneous cluster, the crown defoliation of the tree species showed different and contrasting patterns, changing their relationships with diversity over time. A beneficial role of diversity on defoliation (i.e. decrease of defoliation) has been observed in Quercus ilex, growing in Mediterranean conditions, and Picea abies in Alpine areas after dry periods. In the latter species, drought led to a greater increase in defoliation in monospecific than in mixed stands, suggesting the stabilising role of tree diversity.

Plant growth reduction (GR) is the most widely accepted damage parameter to assess the sensitivity of trees to tropospheric ozone (O3) pollution since it integrates different physiological processes leading to loss of photosynthetic activity and distraction of metabolic resources from growth to defense, repair, and recovery pathways. Because of the intrinsic difficulty to assess the actual O3 risk assessment for forests in field conditions, foliar visible symptoms (FVS) induced by O3 have been proposed as a proxy to estimate possible GR in forest trees. The rationale for this assumption is that the onset of FVS implies a reduction of the photosynthetic capacity of plants. In this review, we show that GR and FVS can be the consequences of independent physiological pathways involving different response mechanisms that can cause both FVS without GR and GR without FVS. The onset of FVS may not lead necessarily to significant GR at plant level for several reasons, including the rise of compensatory photosynthesis, the time lag between growth processes and the accumulation of critical O3 dose, and the negligible effect of a modest amount of injured leaves. Plant GR, on the other hand, may be induced by different physiological mechanisms not necessarily related to FVS, such as stomatal closure (i.e., carbon starvation) to avoid or reduce O3 uptake, and the increase of respiratory processes for the production of metabolic defense compounds. Growth reduction and FVS can be interpreted as different strategies for the acclimation of plants to a stressful environment, and do not mean necessarily damage. Growth reduction (without FVS) seems to prevail in species adapted to limiting environmental conditions, that avoid loss and replacement of injured leaves because of the high metabolic cost of their production; conversely, FVS manifestation (without GR) and the replacement of injured leaves is more common in species adapted to environments with low-stress levels, since they can benefit from a rapid foliar turnover to compensate for the decreased rate of photosynthesis of the whole plant.

The response of PSII and PSI photochemistry to acute ozone (O3) stress was tested in a "model plant system", namely the O3 sensitive (S156) and O3 resistant (R123) genotype pairs of Phaseolus vulgaris L., during a phenological phase of higher O3 sensitivity (pod formation). The modulation of the photosynthetic activity during O3 stress was analysed by measuring gas exchanges, Prompt Fluorescence (PF, JIP-test) and 820 nm Modulated Reflectance (MR), a novel techniques which specifically detects the changes in the redox state of P700 and plastocyanin. The results showed that, coherently with genotypic-specific O3 sensitivity, the response of the two snap bean genotypes differed for the intensity and time of onset of the considered physiological changes. In fact, despite leaf injury and gas exchanges reduction appeared concurrently in both genotypes, S156 showed a PSII down regulation already after the first day of fumigation (DOF), and an enhancement of Cyclic Electron Flow of PSI after the second DOF, whereas R123 showed only slight adjustments until the third DOF, when the activity of both photosystems was down-regulated. Despite these differences, it is possible to distinguish in both genotypes an early O3 response of the photochemical apparatus, involving PSII only, and a following response, in which PSI activity and content are also modulated. The measurement of the MR signal, performed simultaneously with the PF measurements and the JIP-test analysis, has allowed a better understanding of the role that PSI plays in the O3 stress response of the S156/R123 model plant system.

Tree leaves are interfaces between the whole organism and the environment. Leaves display a series of attributes that are linked to specific functions (functional leaf traits—FLT) and/or show responses to biotic and abiotic stress factors (stress response traits, SRT), which can be subdivided into: (a) morphological traits; (b) chemical traits; (c) physiological traits; (d) symptoms. The analysis of FLT is a useful tool for tree species and provenance phenotyping, due to the adaptation of trees to environmental stress. Additionally, FLT can be used as response factor in long term and large spatial scales surveys of forest conditions. Despite these potential benefits of leaf traits in the assessment of ecosystem health and functioning, leaf sampling in forests is time-consuming and costly, especially in forests with a complex vertical and horizontal structure and in remote forest areas. Once a foliar sample has been collected, many different analyses can be carried out; however, analyses should be technically simple and able to be performed within one day following the leaf collection (i.e., on fresh samples), or after air-drying the leaves themselves (analysis of dried specimens). This paper reports the results of leaf sampling and foliar analyses carried out in previous research projects and revises the current state-of-the-art. The leaf traits that are easily obtainable from leaf sampling are listed, together with the operational procedures necessary for their measurement, described in a standardized protocol. Their ecological and functional relevance is discussed in relation to their potential information (as indicators of climatic stress, drought, air and soil pollution, tree light-use and competition, plant nutritional status, health and general plant stress conditions). Finally, this review provides suggestions for the elaboration and reporting of data, and proposes some guidelines to improve the effectiveness of foliar analysis in the assessment of forest ecosystem health, properties and functioning.

Increasing temperatures and drought risks through climate change are expected to have several consequences for European forests. Adaptive strategies may include: (i) persistence of the current forest types, thanks to the acclimatization to local conditions and to phenotypic plasticity of the populations; (ii) evolution, or local adaptation, i.e., change in genotype (frequencies) within the same species due to environmental pressure. It is favored by large within population diversity and (when possible) gene flow among populations; (iii) migration and substitution of species; and (iv) extinction of populations with low ecological plasticity, especially at the edges of their distribution or in the case of isolated (relict) populations. Because of the economic and ecological relevance of forests, it is of fundamental importance to apply appropriate forest management to make forests able to cope with the new environmental conditions. This may include changes in the composition and structure of forest stands, selection of adapted provenances of the most important European tree species or, if this is regarded as insufficient, assisted migration (i.e., the use of species suitable for the future climatic conditions) and, alternatively, substitution of native with non native species. The intraspecific (genetic and phenotypic) variability at a given site has been proven to be often higher than the variability among sites. Species with a large distribution range are supposed to have a wide variety of genotypes, allowing them to be adapted to different environmental conditions. Genetic variability and phenotypic plasticity are the key factors for the identification of useful tree genotypes for future forestation programs. Adaptation to drought, i.e., the probably most important future abiotic risk factor for forestry, can be reflected in variation of key functional traits (FT), at morphological, physiological and phenological level. FT utilized to screen for adapted genotypes in common gardens and provenance trials include growth, survival, leaf flushing and senescence, foliar features as leaf mass per area and nitrogen content, water use efficiency (e.g., estimated by analysis of the stable carbon isotopes, δ 13 C) chlorophyll content, photosystem II functioning, and photosynthetic capacity under water shortage. Current modeled simulation of future forest distribution suggests the expansion of forests at the highest latitudes and altitudes, alongside with a reduction in the hottest and driest Mediterranean regions of South Europe. The general expectations, however, may be disproved especially at a regional level, by factors unexpected or not well known, such as possible extreme climatic events and increased roles of parasites/diseases (with negative effects), or high capacity of forest persistence or adaptation (with positive effects). Natural migration and species substitution can be hampered by co-factors of climate change, such as forest fragmentation and increased frequency and intensity of forest fires.

Humans require multiple services from ecosystems, but it is largely unknown whether trade‐offs between ecosystem functions prevent the realisation of high ecosystem multifunctionality across spatial scales. Here, we combined a comprehensive dataset (28 ecosystem functions measured on 209 forest plots) with a forest inventory dataset (105,316 plots) to extrapolate and map relationships between various ecosystem multifunctionality measures across Europe. These multifunctionality measures reflected different management objectives, related to timber production, climate regulation and biodiversity conservation/recreation. We found that trade‐offs among them were rare across Europe, at both local and continental scales. This suggests a high potential for ‘win‐win’ forest management strategies, where overall multifunctionality is maximised. However, across sites, multifunctionality was on average 45.8‐49.8% below maximum levels and not necessarily highest in protected areas. Therefore, using one of the most comprehensive assessments so far, our study suggests a high but largely unrealised potential for management to promote multifunctional forests., This paper is a joint effort of the working group ‘Scaling biodiversity‐ecosystem functioning relations: a synthesis based on the FunDivEUROPE research platforms’ on the 24th–26th November 2014 in Leipzig, Germany, kindly supported by sDiv, the Synthesis Centre of the German Centre for Integrative Biodiversity Research (iDiv) Halle‐Jena‐Leipzig, funded by the German Research Foundation (FZT 118). The FunDivEUROPE project received funding from the European Union's Seventh Programme (FP7/2007–2013) under grant agreement No. 265171. We thank the MAGRAMA for access to the Spanish Forest Inventory, the Johann Heinrich von Thünen‐Institut for access to the German National Forest Inventories, the Natural Resources Institute Finland (LUKE) for making the Finnish NFI data available, the Swedish University of Agricultural Sciences for making the Swedish NFI data available, and Hugues Lecomte, from the Walloon Forest Inventory, for access to the Walloon NFI data. The study was supported by the TRY initiative on plant traits (http://www.trydb.org).

Urban forests are environmentally, climatically, socially and economically important. An understanding of the response of urban trees to future climate change is crucial to the maintenance of urban forests and the ecosystem services they support. We conducted a controlled environment pot-experiment on four-year-old Mediterranean oak species: the evergreen Quercus ilex and the deciduous Quercus cerris, to investigate the combined impact of elevated CO2 and temperature on growth and leaf physiology to levels predicted for 2050 in urban areas of central Italy. Quercus cerris initially increased net-photosynthesis (PN) under elevated 2050 conditions (EC) compared to present ambient conditions (AC), before PN declined, possibly indicative of down-regulation of photosynthetic physiology. Quercus ilex PN was not influenced by EC throughout the 70 days duration of the study. Levels of PN and stomatal conductance (Gs) were generally lower in Q. ilex than Q. cerris. Quercus ilex also reduced Gs during growth at EC. This reduced transpirative water-loss caused a significant increase in the water use efficiency (WUE) of Q. ilex. This reduction in Gs may have been associated with the observed reduction in stomatal density in Q. ilex grown under EC, while the number of stomata on leaves developed under the experimental conditions were unaffected by the EC treatment in Q. cerris. Over the course of the experiment, above (stem dry weight: SDW) and below-ground biomass (root dry weight: RDW) and foliar starch increased in Q. cerris (in both EC and AC equally) but not Q. ilex. Chlorophyll a fluorescence (ChlF); Prompt Fluorescence (PF), Delayed Fluorescence (DF) and Modulated Reflectance (MR) also indicated that a greater resilience of photochemistry to growth under EC was more apparent in Q. ilex than Q. cerris. In particular, the reduction of the quantum yield efficiency (FV/FM) in Q. ilex may also be considered functional to maintain constant PN levels in elevated temperature and [CO2]. The results of this study suggest that Q. ilex exhibits greater plasticity and adaptation to EC, and may therefore perform more favourably under future 2050 climatic conditions.

Forest health is currently assessed in Europe (ICP Forests monitoring program). Crown defoliation and dieback, tree mortality, and pathogenic damage are the main aspects considered in tree health assessment. The worsening of environmental conditions (i.e., increase of temperature and drought events) may cause large-spatial scale tree mortality and forest decline. However, the role of stand features, including tree species assemblage and diversity as factors that modify environmental impacts, is poorly considered. The present contribution reanalyses the historical dataset of crown conditions in Italian forests from 1997 to 2014 to identify ecological and structural factors that influence tree crown defoliation, highlighting in a special manner the role of tree diversity. The effects of tree diversity were explored using the entire data set through multivariate cluster analyses and on individual trees, analysing the influence of the neighbouring tree diversity and identity at the local (neighbour) level. Preliminary results suggest that each tree species shows a specific behaviour in relation to crown defoliation, and the distribution of crown defoliation across Italian forests reflects the distribution of the main forest types and their ecological equilibrium with the environment. The potentiality and the problems connected to the possible extension of this analysis at a more general level (European and North American) were discussed.

Increased rate of reactive oxygen species (ROS) is a common plant response to various environmental stresses. In chloroplast thylakoids, the reaction centers of photosystems I and II are the major generation site of ROS. In the present study, the changes of chlorophyll a fluorescence parameters, P700 absorption change and ROS production (using the fluorescent probe 2,7-dichlorofluorescin diacetate) were investigated in Lemna gibba plants exposed to salt stress (0–400 mM NaCl). Salt stress inhibited PSI and PSII activities and resulted in a decrease in overall activity of the electron transport chain while stimulating ROS production. When L. gibba plants were kept into dark condition, NaCl treatment did not showed any significant change in ROS formation compared to control. However, NaCl treatment in light condition induced a strong increase in ROS formation. The production of ROS at 400 mM NaCl was 2.6 and 10 fold higher compared to the control respectively after 6 h and 24 h treatment in light. Furthermore, the correlation between ROS production and the two photosystems (PSI and PSII) activities in L. gibba plants was analyzed. Our data confirmed the correlation between the ROS production and PSII and PSI activities. We showed that ROS production was highly correlated to maximal quantum yield of PSII (R2 = 0.91) and efficiency with which a trapped exciton can move an electron into the electron transport chain (R2 = 0.86). While the correlation coefficient (R2) value ROS formation and ΔI/Io 820 nm (measure of redox states of plastocyanin and P700) was 0.63.

Plants, under stressful conditions, can proceed to photosynthetic adjustments in order to acclimatize and alleviate the detrimental impacts on the photosynthetic apparatus. However, it is currently unclear how adjustment of photosynthetic processes under environmental constraints by plants influences CO2 gas exchange at the ecosystem-scale. Over a 2-year period, photosynthetic performance of a temperate grassland ecosystem was characterized by conducting frequent chlorophyll fluorescence (ChlF) measurements on three primary grassland species (Lolium perenne L., Taraxacum sp., and Trifolium repens L.). Ecosystem photosynthetic performance was estimated from measurements performed on the three dominant grassland species weighed based on their relative abundance. In addition, monitoring CO2 fluxes was performed by eddy covariance. The highest decrease in photosynthetic performance was detected in summer, when environmental constraints were combined. Dicot species (Taraxacum sp. and T. repens) presented the strongest capacity to up-regulate PSI and exhibited the highest electron transport efficiency under stressful environmental conditions compared with L. perenne. The decline in ecosystem photosynthetic performance did not lead to a reduction in gross primary productivity, likely because increased light energy was available under these conditions. The carbon amounts fixed at light saturation were not influenced by alterations in photosynthetic processes, suggesting photosynthesis was not impaired. Decreased photosynthetic performance was associated with high respiration flux, but both were influenced by temperature. Our study revealed variation in photosynthetic performance of a grassland ecosystem responded to environmental constraints, but alterations in photosynthetic processes appeared to exhibit a negligible influence on ecosystem CO2 fluxes.

The importance of biodiversity in supporting ecosystem functioning is generally well accepted. However, most evidence comes from small‐scale studies, and scaling‐up patterns of biodiversity–ecosystem functioning (B‐EF) remains challenging, in part because the importance of environmental factors in shaping B‐EF relations is poorly understood. Using a forest research platform in which 26 ecosystem functions were measured along gradients of tree species richness in six regions across Europe, we investigated the extent and the potential drivers of context dependency of B‐EF relations. Despite considerable variation in species richness effects across the continent, we found a tendency for stronger B‐EF relations in drier climates as well as in areas with longer growing seasons and more functionally diverse tree species. The importance of water availability in driving context dependency suggests that as water limitation increases under climate change, biodiversity may become even more important to support high levels of functioning in European forests., The FunDivEUROPE project received funding from the European Union Seventh Programme (FP7/2007–2013) under grant agreement No. 265171. Additional support was received from the German Centre for Integrative Biodiversity Research (iDiv) Halle‐Jena‐Leipzig for SR. CW acknowledges the support of the Max‐Planck‐Society.

Many morphological, chemical and physiological indicators have been proposed to evaluate the conditions of plants in ecological systems. Among them, the analysis of the prompt fluorescence (PF) of chlorophyll is considered a powerful tool that combines the richness of the achievable information with the operational quickness. This technique is especially suitable in large ecological surveys, where it is required to screen many samples in a brief time. The PF allows evaluating photochemical properties and functionalities of photosynthetic organisms utilizing a set of parameters, known as ‘JIP-test’. The distinct phases of the photochemical processes in terms of energy absorption, trapping and electron transport can be described by these parameters. In this paper, we re-analyse large PF datasets obtained in past researches, carried out in field conditions (forests, plantations and pasture meadows) and in experimental setups (semi-controlled conditions). The aim was to explore the relationships (redundancy and independence) among the JIP-test parameters to select the most suitable ones to capture the variability of plant photosynthetic efficiency and their responses to environmental pressures. The Principal Component Analysis (PCA) was applied to 43,987 measurements. The overall PCA results evidenced that the variability of the PF parameters is explicated mainly by two factors, connected respectively to the processes of photon capture and first photochemical events, and to the efficiency of the electron transport around the photosystem I. This result suggests that, in ecological studies, the photosynthetic functioning of the member of a population can be effectively described with two parameters representative of these two phases: the maximum quantum yield of primary photochemistry of a dark-adapted sample (FV/FM) and the amplitude of the I-P phase (ΔVIP). FV/FM and ΔVIP probed to be independent and their correlation in various datasets may be either positive or negative in relation to the environmental factors considered. The physiological significance of the correlations between these parameters is discussed.

Nine short-term independent studies were carried out with two M-PEA units on several plant species differing in their functional traits (woody evergreen, woody deciduous, herbaceous) and exposed to different kind of abiotic stress (drought, salt, ozone, UV radiation). Aim of the study is to check the consistency of plant responses, assessed through three sets of simultaneously measured signals: Prompt Fluorescence (PF), Delayed Fluorescence (DF) and Modulated Reflectance of 820 nm light (MR). The decrease of FV/FM and F0, the increase of VJ and VI were the most common responses related to PF parameters. The decrease of vox and vred as well the increase of MRmin were common response of MR. DF showed species-treatment specific behaviours. The Principal Component Analysis (PCA) suggests that the combination of PF and MR parameters represents a powerful tool for plant stress phenotyping, whereas MR parameters are linked to physiological strategies, related to different functional groups, to cope with stress factors.

a b s t r a c t Forecasting models for climate change in southern Europe differ from those proposed for central and northern regions mainly with regard to precipitation. In fact, a strong reduction in average rainfall, mainly caused by decrease frequency of rainy events, is believe to occur in the Mediterranean basin in the forthcoming hundred years. Increased frequency of drought events will be paralleled and exacerbated by warming. Differently from areas where plant growth is limited by sub-optimal temperature (i.e. boreal and most temperate forests) and where warming has been reported to increase carbon assimilation and growth, plants growing in the Mediterranean basin are currently near their temperature optimum, and warming may contribute (e.g. with drought) to impair photosynthesis and depress growth and survival. Rising atmospheric CO2 has been found to increase growth, photosynthesis water use efficiency, and may partially alleviate the deleterious effects of warming and drought. However, in areas where severe and prolonged drought episodes occur, severe photoinhibition and metabolic limitation to photosynthesis may prevent Mediterranean sclerophylls to take advantage of higher atmospheric CO2, and may slow down recovery after the end of the dry season. The most sensitive forest types consist in tree species which are, in the Mediterranean basin, at the southernmost limit of their distribution range. In contrast, thermophilous trees are expected to have a greater diffusion both in southern and central Europe, as winter cold stress will be reduced by warming. Yet due to great variability of ecological features, the alleged substitution of tree species can follow a natural pattern from south to north and from low to high altitudes, without considering obstacles deriving from urbanization. For these reasons, research on the performance and ecologic plasticity of different genotypes, on species selection, and on planting and management techniques can have strategic importance for adaptive forest management. © 2013 Elsevier B.V. All rights reserved.