Anatomical adjustment of mature leaves of sycamore maple (Acer pseudoplatanus L.) to increased irradiance

Trees regenerating in the understory respond to increased availability of light caused by gap formation by undergoing a range of morphological and physiological adjustments. These adjustments include the production of thick, sun-type leaves containing thicker mesophyll and longer palisade cells than in shade-type leaves. We asked whether in the shade-regenerating tree Acer pseudoplatanus, the increase in leaf thickness and expansion of leaf tissues are possible also in leaves that had been fully formed prior to the increase in irradiance, a response reported so far only for a handful of species. We acclimated potted seedlings to eight levels (from 1 to 100%) of solar irradiance and, in late summer, transferred a subset of them to full sunlight. Within 30 days, the shaded leaves increased leaf mass per area and became thicker mostly due to elongation of palisade cells, except for the most shaded individuals which suffered irreversible photo-oxidative damage. This anatomical acclimation was accompanied by partial degradation of chlorophyll and a transient decline in photosynthetic efficiency of PSII (Fv/FM). These effects were related to the degree of pre-shading. The Fv/FM recovered substantially within the re-acclimation period. However, leaves of transferred plants were shed significantly earlier in the fall, indicating that the acclimation was not fully effective. These results show that A. pseudoplatanus is one of the few known species in which mature leaves may re-acclimate anatomically to increased irradiance. This may be a potentially important mechanism enhancing utilization of gaps created during the growing season.

The Occurrence of Apiognomonia hystrix and Its Pathogenicity towards Acer pseudoplatanus and Fraxinus excelsior under Field Conditions

Apiognomonia hystrix is an ascomycetous fungus within Diaporthales that is found on maples and to a lesser extent on other hardwood trees in Europe, Northern America and Asia. To date, varying opinions on the species’ status as a cause of plant diseases have been expressed. In this study, we present the results of analyses conducted from 2012–2017 at forest sites in Poland on the occurrence of A. hystrix on Acer pseudoplatanus and Fraxinus excelsior and the pathogenicity of this fungus towards both tree species. For the sycamore leaves, A. hystrix conidiomata were detected in connection with 19.2% of galls caused by Dasineura vitrina, 20.4% of galls caused by Drisina glutinosa and 67.9% of extensive vein-associated necroses. The A. hystrix colonization of galls caused by both midge species resulted in statistically significantly larger necroses. On European ash leaves, conidiomata of A. hystrix occurred in connection with 0.8% of Dasineura fraxinea galls. Perithecia of A. hystrix were detected on overwintered leaf petioles in 8.1% of A. pseudoplatanus and 1.2% of F. excelsior samples. Twelve representative cultures were characterized molecularly by barcoding three marker genes (ITS, ACT, CAL). Results of phylogenetic analyses indicate that A. hystrix isolates are genetically variable, and three lineages are distinguishable. Eight isolates, including four originating from sycamore and four from European ash, were used to determine A. hystrix pathogenicity. Among the 48 A. pseudoplatanus petioles inoculated with A. hystrix, 41 developed necrotic lesions after 8 weeks, with the average necrosis length caused by particular isolates ranging from 14.5 to 67.2 mm. None of the 48 inoculated F. excelsior petioles developed necrotic lesions. Finally, selected aspects of A. hystrix morphology on natural substrates and in vitro are discussed in this paper, as well as the species’ potential to cause disease symptoms.

Native seed dispersal by rodents is negatively influenced by an invasive shrub

Refuge–mediated apparent competition is the mechanism by which invasive plants increase pressure on native plants by providing refuge for generalist consumers. In the UK, the invasive Rhododendron ponticum does not provide food for generalist seed consumers like rodents, but evergreen canopy provides refuge from rodent predators, and predation and pilferage risk are key factors affecting rodent foraging and caching behaviour. Here we used a seed removal/ seed fate experiment to understand how invasion by an evergreen shrub can alter seed dispersal, seed fate and early recruitment of native trees. We used seeds of four species, small and wind–dispersed (sycamore maple Acer pseudoplatanus and European ash Fraxinus excelsior) and large and animal–dispersed (pedunculate oak Quercus robur and common hazel Corylus avellana), and monitored seed predation and caching in open woodland, edge habitats, and under Rhododendron. In the open woodland, wind–dispersed seeds had a higher probability of being eaten in situ than cached seeds, while the opposite occurred with animal–dispersed seeds. The latter were removed from the open woodland and edge habitats and cached under Rhododendron. This pattern was expected if predation risk was the main factor influencing the decision to eat or to cach a seed. Enhanced dispersal towards Rhododendron cover did not increase the prospects for seed survival, as density of hazel and oak saplings under its cover was close to zero as compared to open woodland, possibly due to increased cache pilferage or low seedling survival under dense shade, or both. Enhanced seed predation of ash and sycamore seeds close to Rhododendron cover also decreased recruitment of these trees. Rhododendron patches biased rodent foraging behaviour towards the negative (net predation) side of the conditional rodent / tree interaction. This effect will potentially impact native woodland regeneration and further facilitate Rhododendron spread due to refuge–mediated apparent competition.

Effects of pretreatment, sowing time, sowing environment and climate factors on germination in Acer pseudoplatanus L.

In this study, the effects of different sowing environment (greenhouse and nursery), pretreatment (cold moist stratification), different sowing time (autumn, spring and summer) and some climate factors (air temperature, relative air humidity, soil temperature and soil moisture) on the germination of Acer pseudoplatanus L. seeds were studied. Seeds were harvested from the tree located in the Karadeniz Technical University campus. Three different germination trials were carried out; (1) direct sowing in autumn after seed collection (Control), (2) sowing stratified seeds in spring (Stratification-1) and (3) sowing stratified seeds in summer (Stratification-2). During the germination trial processes, air temperature, relative air humidity, soil temperature and soil moisture were measured periodicaly. Thus, the germination percentage changes in different sowing environments have been established on the basis of some climate factors. Higher germination percentages were obtained in the autumn (Control) compared to the spring (Stratification-1) and summer (Stratification-2) sowings. The highest percentages of germination were ­determined in the control trials (70% in greenhouse and 58% in nursery). Obtained germination results based on different sowing times revealed secondary dormancy in Acer pseudoplatanus L. seeds. It has been determined that the mean germination time in the greenhouse (12 days) was shorter than the mean germination time in the nursery (18 days). In addition, the obtained results showed that stratification and sowing time have a positive effect on the mean germination time in the greenhouse. Because of getting the best germination rates, keeping some climate ­factors constant (21.0-24.9 °C air temperature; 17.0-19.9 °C soil temperature; 63.0-68.9% relative air humidity; 60.0-67.9% soil moisture) during the vegetative propagation practices in the greenhouse, should affect mass ­seedling production in Acer pseudoplatanus L.

Wavelength-dependent photodegradation of wood and its effects on fluorescence

Apart from some strongly fluorescent wood species, the general fluorescence of wood has long been ignored. Recent studies suggest that each species has a distinct fluorescence, originating from both basic components and characteristic extractives. However, wood colour and fluorescence rapidly change upon exposure to sunlight. In this study, 288 samples of Acer pseudoplatanus, Quercus robur, Picea abies and Juglans nigra were irradiated with different bands of ultraviolet (UV) and visible (VIS) light. Photosensitivity was examined in regards of colour, infrared absorbance (FTIR), and fluorescence imaging. UV light caused strong yellowing in all examined species, mostly correlating with lignin degradation, carbonyl formation and the appearance of a broad banded fluorescence emission. VIS light above 420 nm, however, caused different, partly contradicting effects in colour and fluorescence, and did not affect lignin. J. nigra proved to be most sensitive towards VIS-induced yellowing and bleaching. The main new finding of this study is that the native long wave fluorescence of wood was strongly decreased by VIS-irradiation above 510 nm wavelength in all samples. This effect was not species-specific, probably originating from a cross-species wood component. The results have potential impacts on non-destructive image-based evaluation methods and wood identification.

Survival time and mortality rate of regeneration in the deep shade of a primeval beech forest

Low mortality rates and slow growth differentiate shade-tolerant from shade-intolerant species and define the survival strategy of juvenile trees growing in deep shade. While radial stem growth has been widely used to explain mortality in juvenile trees, the leaf area ratio (LAR), known to be a key component of shade tolerance, has been neglected so far. We assessed the effects of LAR, radial stem growth and tree height on survival time and the age-specific mortality rate of juvenile Fagus sylvatica L. (European beech), Acer pseudoplatanus L. (sycamore maple) and Acer platanoides L. (Norway maple) in a primeval beech forest (Ukraine). Aboveground and belowground biomass and radial stem growth were analysed for 289 living and 179 dead seedlings and saplings. Compared with the other species, F. sylvatica featured higher LAR, slower growth and a lower mortality rate. The average survival time of F. sylvatica juveniles (72 years) allows it to reach the canopy more often than its competitors in forests with low canopy turnover rate. In contrast, a combination of lower LAR, higher growth rate and higher age-specific mortality rate of the two Acer species resulted in their shorter survival times and thus render their presence in the canopy a rare event. Overall, this study suggests that shade tolerance, commonly defined as a relationship between sapling mortality and growth, can alternatively be formulated as a relationship between survival time and the interplay of growth and LAR.

Woody and Foliage Biomass, Foliage Traits and Growth Efficiency in Young Trees of Four Broadleaved Tree Species in a Temperate Forest

The main goal of this study is to analyse and interpret interspecific differences in foliage biomass/area and woody parts biomass as well as the ratio between quantities of foliage and woody components (i.e., branches, stem and roots). The study was principally aimed at determining basic biomass allocation patterns and growth efficiency (GE) of four broadleaved species, specifically common aspen (Populus tremula L.), European hornbeam (Carpinus betulus L.), silver birch (Betula pendula Roth.) and sycamore (Acer pseudoplatanus L.) in young growth stages. We performed whole-tree sampling at 32 sites located in central and northern parts of Slovakia. We sampled over 700 trees and nearly 4900 leaves to quantify biomass of woody parts and foliage traits at leaf and tree levels. Moreover, we estimated specific leaf area in three parts of the crown, i.e., the upper, middle and lower thirds. We found that hornbeam had the largest foliage biomass and the lowest foliage area of all investigated species, while its biomass of woody parts did not differ from aspen and sycamore. Birch had the lowest biomass of woody parts, although its foliage properties were similar to those of aspen. Intraspecific differences of foliage were related to tree size and to leaf position along the vertical crown profile. Growth efficiency (GE), expressed as woody biomass production per foliage area unit, was evidently larger in hornbeam than in the other three broadleaves. We suggest that future GE modelling should utilize real values of stem diameter increment measured in a current year, bio–sociological position of trees and competition indicators as inputs. Such an approach would elucidate the role of stand structure and tree species mixture for ecological and production properties of forest stands.

A 30-year update of the climbers and vascular epiphytes inventory of the Cerro Ñielol Natural Monument (La Araucanía, Chile): a database

Plant species diversity may be seriously threatened in ecotone zones under global climate change. Therefore, keeping updated inventories of indicator species seems to be a good strategy for monitoring wild areas located in these strips. The database comes from an inventory of climbers and vascular epiphytes conducted in the Cerro Ñielol Natural Monument, a small protected area (89 hectares) located in Chile's Mediterranean-temperate phytogeographic region, within the boundaries of the city of Temuco, La Araucaína Region. The data represent the update of the first inventory carried out between 1980 and 1984. In this current contribution, data collection was carried out in 27 quadrats using the trails as transects. The data provide the record of 45 species (16 climbers, 15 epiphytes and 10 trees), including two accidental epiphytes (Acer psudoplatanus L. and Gavilea odoratissima (L.) Endl. ex Griseb.), two species that can be found as epiphytes or terricolous (Hymenophyllum tunbrigense (L.) Sm. and Nertera granadensis (Mutis ex L.f.) Druce) and one species (Chusquea quila Kunth) that can be found as terricolous and climber. Species of interest were recorded on live trees (n = 51), snags (n = 9), stumps (n = 4), fallen log (n = 5) and on the forest soil (n = 17). The most abundant climbers were Hydrangea serratifolia (Hook. & Arn.) F. Phil. (n = 77 stems), Lapageria rosea Ruiz & Pav. (n = 70 stems), Raukaua valdiviensis (Gay) Frodin (n = 48 stems) and Cissus striata Ruiz & Pav. (n = 33 stems). In contrast, the most abundant epiphytes were Hymenophyllum plicatum Kaulf. (n = 1728 fronds) and Hymenophyllum tunbrigense (L.) Sm. (n = 2375 fronds). These latter two species represent the highest frequency and abundance in the whole inventory, respectively. Several ecosystem traits are, in fact, new reports since the first inventory was conducted in 1980-1984; for example, the presence of the filmy fern Hymenophyllum tunbrigense, the record of the climber Elytropus chilensis , fallen logs or the species-host relationship. Accordingly, the database is made available in this manuscript. This study updates the climbers and vascular epiphyte species list in the Cerro Ñielol Natural Monument, a small patch of forest under severe anthropogenic pressure. This protected area is characterised by floristic elements of the Mediterranean and temperate phytogeographic region of Chile, in a zone where forests have been severely deforested. The database includes the record of 45 species – including six species that were not recorded in the first inventory – in 211 records. The main novelty of this contribution is the systematic classification of species, on ten traits rarely reported in a floristic inventory: (i) species taxonomic identity (as usual), (ii) species abundance (number of stems and fronds), (iii) habit (herb, shrub, subshrub, tree), (iv) growth form (accidental epiphyte, epiphyte, vine, liana, terricolous), (v) climbing mechanism (tendrils, adhesive roots, twining, scrambling), (vi) microhabitat (fallen log, footpath slope, soil, stump, trunk), (vii) host species (where appropriate), (viii) host condition (live, woody debris, snag), (ix) host diameter at breast height (DBH) and (x) target species found over 2.3 m on trees. Thirty years after the first inventory conducted between 1980 and 1984, the climber assemblage has remained relatively stable over time, although there are some differences in species composition. Specifically, the climber Elytropus chilensis are recorded in the current inventory, but the Mitraria coccinea (recorded in the first inventory) is not present. On the other hand, the epiphyte assemblage showed an increase in the species richness of filmy ferns, with five previously unrecorded species: Hymenophyllum cuneatum, H. dicranotrichum, H. pectinatum, H. peltatum and H. tunbrigense. One of the novel features was the presence of Sarmienta scandens and Synammia feuillei on a Pinus radiata D. Don tree. Additionally, the introduced species Acer pseudoplatanus is included, which is new to the Chilean vascular plant catalogue. All these data are available in the present manuscript.

Effect of Climate Change on the Growth of Endangered Scree Forests in Krkonoše National Park (Czech Republic)

Scree forests with large numbers of protected plants and wildlife are seriously threatened by climate change due to more frequent drought episodes, which cause challenges for very stony, shallow soils. The effect of environmental factors on the radial growth of five tree species—European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst.), sycamore maple (Acer pseudoplatanus L.), European ash (Fraxinus excelsior L.), and mountain elm (Ulmus glabra Huds.)—was studied in the mixed stands (105–157 years) in the western Krkonoše Mountains (Czech Republic) concerning climate change. These are communities of maple to fir beechwoods (association Aceri-Fagetum sylvaticae and Luzulo-Abietetum albae) on ranker soils at the altitude 590–700 m a.s.l. Production, structure, and biodiversity were evaluated in seven permanent research plots and the relationships of the radial growth (150 cores) to climatic parameters (precipitation, temperature, and extreme conditions) and air pollution (SO2, NOX, ozone exposure). The stand volume reached 557–814 m3 ha−1 with high production potential of spruce and ash. The radial growth of beech and spruce growing in relatively favorable habitat conditions (deeper soil profile and less skeletal soils) has increased by 16.6%–46.1% in the last 20 years. By contrast, for sycamore and ash growing in more extreme soil conditions, the radial growth decreased by 12.5%–14.6%. However, growth variability increased (12.7%–29.5%) for all tree species, as did the occurrence of negative pointer years (extremely low radial growth) in the last two decades. The most sensitive tree species to climate and air pollution were spruce and beech compared to the resilience of sycamore and ash. Spectral analysis recorded the largest cyclical fluctuations (especially the 12-year solar cycle) in spruce, while ash did not show any significant cycle processes. The limiting factors of growth were droughts with high temperatures in the vegetation period for spruce and late frosts for beech. According to the degree of extreme habitat conditions, individual tree species thus respond appropriately to advancing climate change, especially to an increase in the mean temperature (by 2.1 °C), unevenness in precipitation, and occurrence of extreme climate events in the last 60 years.

Nemoralisation of Pinus sylvestris and Picea abies Forest Stands in the Hemi-Boreal Zone: A Case Study from Latvia

At the beginning of the 21st century, in extensively managed mature and over-mature conifer stands (Pinus sylvestris and Picea abies) in Latvia, establishment of native deciduous broad-leaved (Acer platanoides, Tilia cordata, Quercus robur and Ulmus laevis), as well as alien broad-leaved species (Acer pseudoplatanus and Tilia platyphyllos) has been observed. The establishment of deciduous broad-leaved species in coniferous stands is a process known as nemoralisation of coniferous stands, which is characterised by a large number of seedlings of broad-leaved species, young trees and the formation of a subcanopy layer in stands. Based on the age measurements of individuals of broad-leaved species trees, the establishment of some individuals into the studied coniferous stands occurred 40–50 years ago — in the 1970s–1980s. However, the predominant age of alien broad-leaved tree species in the study plots was 15–25 years, i.e. the introduction of large numbers of seedlings of these species in the coniferous stands occurred at the end of the 20th century. In this manner, in the final phase of the conifer replacement process, stable, mostly shade tolerant, mixed stands consisting of 3–4 species have formed, in which spruce is often found together with broad-leaved species.