Molecular evidence for hybrid origin of Quercus crenata Lam. (Fagaceae) from Q. cerris L. and Q. suber L.

Abstract

Random Amplified Polymorphic DNA (RAPD) and Inter-Simple Sequence Repeats (ISSR) markers were employed to examine samples from Quercus cerris, Q. suber and Q. crenata in order to test the hypothesis of the hybrid origin of Q. crenata from Q. cerris and Q. suber in a part of its distribution area where the two putative parents do not overlap at present. Leaves from 21 Q. crenata and 37 Q. cerris individual trees were collected at natural sites in northern Italy, where Q. suber is currently lacking; 21 Q. suber and six Q. crenata plants from central Italy were also analysed. Results from Unweighted Pair Group Method with Arithmetic mean (UPGMA) analysis and principal component analysis (PCA) implied that exchange of neutral markers has been considerable between the three species, while differences in morphological characters have remained comparatively stable. The Mantel test indicated low correlation between RAPD- and ISSR-based similarity matrices, showing that the two screening techniques reveal unrelated estimates of genetic relationships. Hybrid indices computed for both markers displayed an intermediate position of Q. crenata individuals between the two putative parents shifted toward Q. cerris. Results from the present study corroborate the hypothesis of a hybrid origin for Q. crenata occurring in northern Italy, and suggest asymmetrical backcrossing with Q. cerris acting as the recurrent parent.     

Leaf Water Potential and Peroxidase activity in Quercus cerris and Quercus pubescens after Inoculation with Diplodia mutila

Ten-year-old field-grown Quercus pubescens Willd. and Quercus cerris L. individuals were inoculated with Diplodia mutila (teleomorph Botryosphaeria stevensii Shoe-maker) to observe symptom evolution over 2 years. The experiments were carried out for the 3 years: 1991, 1992 and 1993. At the same time, the effect of D. mutila on leaf water potential and peroxidase activity was assessed on the leaves of 2-year-old seedlings from the same two species growing under controlled conditions (18 h day, relative humidity 75%), temperature 24/15°C day/night). Quercus pubescens was more susceptible than Q. cerris, and frequently exhibited dieback of the branch above the inoculation site. On the seedlings, the visible symptoms of infection were much more severe than on the older trees. The infected seedlings showed a lower leaf water potential than healthy seedlings, particularly those of Q. pubescens after the third week. The peroxidase activity was increased in infected Q. pubescens seedlings compared with both groups of control seedlings (wounded but not inoculated, and neither wounded nor inoculated) 14 and 21 days after inoculation. Leaf water potential and peroxidase activity are known indicators of stress which appear even before any visible symptoms; they could therefore serve as early indicators of D. mutila infection.     

Seasonal variations of gas exchange, photosynthetic pigments, and antioxidants in Turkey oak (Quercus cerris L.) and Hungarian oak (Quercus frainetto Ten.) of different age

Seasonal changes in physiological and biochemical parameters were studied in 35-, 55- and 140-year-old trees of Turkey oak (Quercus cerris L.) and Hungarian oak (Q. frainetto Ten.), growing in natural stands in Eastern Balkan Mountains (Bulgaria). During the seasonal drought period (August), assimilation activity, transpiration rate, stomatal conductance and water potential had a seasonal minimum in all the studied tree ages and species. The foliar concentrations of glutathione, ascorbate, α-tocopherol, as well as photosynthetic pigments in oak leaves were significantly affected by season. With the increasing age of the studied trees, we observed a decrease of the physiological activity and an increase of the antioxidants’ accumulation. Both the species were drought tolerant and anisohydric, where Q. frainetto exhibited higher rates of gas exchange than Q. cerris. Moreover, they differed in the extent of increase in the foliar antioxidants and carotenoids.     

Impacts of elevated atmospheric CO2 on litter quality, litter decomposability and nitrogen turnover rate of two oak species in a Mediterranean forest ecosystem

Elevated CO₂ may affect litter quality of plants, and subsequently C and N cycling in terrestrial ecosystems, but changes in litter quality associated with elevated CO₂ are poorly known. Abscised leaf litter of two oak species (Quercus cerris L. and Q. pubescens Willd.) exposed to long-term elevated CO₂ around a natural CO₂ spring in Tuscany (Italy) was used to study the impact of increasing concentration of atmospheric CO₂ on litter quality and C and N turnover rates in a Mediterranean-type ecosystem. Litter samples were collected in an area with elevated CO₂ (>500 ppm) and in an area with ambient CO₂ concentration (360 ppm). Leaf samples were analysed for concentrations of total C, N, lignin, cellulose, acid detergent residue (ADR) and polyphenol. The decomposition rate of litter was studied using a litter bag experiment (12 months) and laboratory incubations (3 months). In the laboratory incubations, N mineralization in litter samples was measured as well (125 days). Litter quality was expressed in terms of chemical composition and element ratios. None of the litter quality parameters was affected by elevated CO₂ for the two Quercus species. Remaining mass in Q. cerris and Q. pubescens litter from elevated CO₂ was similar to that from ambient conditions. C mineralization in Q. pubescens litter from elevated CO₂ was lower than that from ambient CO₂, but the difference was insignificant. This effect was not observed for Q. cerris. N mineralization was higher from litter grown at elevated CO₂, but this difference disappeared at the end of the incubation. Litter of Q. pubescens had a higher quality than Q. cerris, and indeed mineralized more rapidly in the laboratory, but not under field conditions.     

Fungal Endophytic Communities in Healthy and Declining Quercus robur L. and Q. cerris L. Trees in Northern Italy

Healthy and declining English oak (Quercus robur) and Turkey oak (Q. cerris) in north‐western Italy, in a plain oak forest showing decline for oak puzzle disease, were tested to assess possible variations in the composition of their fungal endophytic communities and their relation to the health status of trees. Samples collected in spring (buds) and in autumn (leaves, annual shoots and twigs) were surface‐sterilized, cut into fragments and placed on potato dextrose agar for a month; 26 fungal species were isolated, the most frequent being Tubakia dryina, Dendrodochium sp., Eutypella sp. and a sterile mycelium. Correspondence analysis showed significant qualitative differences between assemblages inhabiting twigs and herbaceous tissues that were due to the low frequency of Tubakia dryina in twigs and its higher frequency in buds, leaves and shoots. Tubakia dryina was isolated more frequently from leaves of declining oaks and from buds of healthy oaks; Monochaetia monochaeta showed a preference for healthy trees, especially leaves and buds. According to the Shannon–Wiener index, endophytic fungal communities of leaves, twigs and buds of declining English oak were poorer than those of declining Turkey oak, but there were no significant differences between healthy hosts.     

Establishment of co‐existing Mediterranean tree species under a varying soil moisture regime

We investigated the responses of two co‐existing Mediterranean trees with different regeneration strategies (Phillyrea latifolia seedlings and Quercus ilex sprouts) to experimental drought below the forest canopy. We considered different recruitment stages and used leaf isotopic discrimination to estimate water use efficiency (WUE) and nitrogen availability and use. Drought decreased the emergence and survival of seedlings and sprouts. Survival and growth of older saplings were not influenced by drought. Seedling emergence of P. latifolia was higher than Q. ilex sprout production, but Q. ilex sprouts had higher survival and growth rates. These differences disappeared in the sapling stage. Carbon isotopic discrimination suggested that Q. ilex sprouts had higher WUE than P. latifolia seedlings. Drought increased WUE of recruits, particularly in Q. ilex. Water use regulation increased with ageing, particularly in P. latifolia. Q. ilex had higher δ¹⁵N values than P. latifolia; these were also higher under drier soil conditions. Current year seedlings had higher δ¹⁵N than saplings, particularly in P. latifolia, suggesting they exploit superficial soil layers. These results suggest that sprouts obtain benefit from resources stored in parent plants. At earlier stages, they perform better than seedlings. This response is not coupled to adult vulnerability to drought for these species, revealing the difficulty of predicting species dynamics during climate change.     

Light-guiding function of foliar sclereids in the evergreen sclerophyll Phillyrea latifolia: a quantitative approach

The anatomy and orientation of the foliar sclereids of the evergreen sclerophyll Phillyrea latifolia suggest a light-guiding function. Light microscope observations of enzymatically isolated sclereids showed that they possessed very thick cell walls, lobes and branches which occurred mainly at the end of the idioblasts reaching the abaxial epidermis. Leaf cross-sections showed that sclereids occurred diffusely within the mesophyll and were oriented vertically with respect to the lamina. In paradermal sections, the cut cell walls of the sclereids appeared as bright light spots among the dark-green background of the mesophyll cells. The heterogeneity of the radiation field transmitted through the same paradermal section was quantified by image analysis and two- or three-dimensional representations. The amount of light transmitted through the sclereids was found to be up to 30-fold higher compared to that transmitted through the neighbouring mesophyll cells. The light guiding capacity of the sclereids at the spongy mesophyll level was estimated to be 40-80%. In leaves illuminated from the adaxial surface, light passing through the ends of the sclereids seemed to be reflected from the internal surface of the abaxial epidermis. In sunny conditions when leaf thickness tends to increase, the number of sclereids per unit leaf area was increased significantly compared to the shaded ones. It is proposed that the anatomy and orientation of the foliar osteosclereids of P. latifolia, are suitable for a light-guiding function. Thus foliar sclereids, besides other roles, may contribute both qualitatively and quantitatively, to the enhancement of the light microenvironment within the mesophyll of these sclerophyllous leaves.Keywords: Phillyrea latifolia L. (incl. P. media L.), foliar sclereids, light guiding, image analysis.      

Nutrient content and seasonal fluctuations in the leaf component of coark-oak (Quercus suber L.) litterfall

Nutrient content and seasonality of the leaf component in cork-oak litterfal were studied over a two year period in two cork-oak forest sites differing in biomass and edaphic condition in the north-eastern Iberian peninsula. Fallen senescent leaves compared to young leaves showed higher non-mobile nutrient concentrations and lower mobile nutrient concentrations, specially P, N, K, and Mg. At both sites, seasonal fluctuations affected both leaf production and leaf mineral content. The maximum leaf fall period correspond to the start of the vegetative growth and to the lowest N and P concentration in the falling leaves. The opposite was true for the winter, when litterfal was minimal and N and P content in falling leaves was at a maximum.The comparison between falling leaves and canopy leaves suggests that the analysis of fallen leaves can be a useful measure of N and P nutrition in cork-oak. We found site dependent differences in nutrient content and nutrient remobilization. In comparison with Q. ilex, although litter production was in the same range, nutrient retranslocation was greater for Q. suber.     

Contrasting foliar responses to drought in Quercus ilex and Phillyrea latifolia

Leaf morphology, longevity, and demography were examined in Quercus ilex and Phillyrea latifolia growing in a holm oak forest in Prades mountains (northeast Spain). Four plots (10 × 15 m) of this forest were submitted to an experimental drought during three years (soil moisture was reduced about 15 %). Leaf area, thickness and leaf mass per area ratio (LMA) were measured in sun and shade leaves of both species. Leaf longevity, the mean number of current-year shoots produced per previous-year shoot (Sn/Sn-1), the mean number of current-year leaves per previous-year shoot (Ln/Sn-1), and the percentage of previous-year shoots that developed new ones were measured once a year, just after leaf flushing. LMA and leaf thickness increased since leaf unfolding except in summer periods, when stomatal closure imposed low photosynthetic rates and leaves consumed their reserves. LMA, leaf area, and leaf thickness were higher in Q. ilex than in P. latifolia, but leaf density was higher in the latter species. Drought reduced the leaf thickness and the LMA of both species ca. 2.5 %. Drought also increased leaf shedding up to ca. 20 % in Phillyrea latifolia and decreased it up to ca. 20 % in Q. ilex. In the later species, Sn/Sn-1 decreased by 32 %, Ln/Sn-1 by 41 %, percentage of shoots developed new ones by 26 %, and leaf area by 17 %. Thus the decrease of leaf number and area was stronger in the less drought-resistant Q. ilex, which, under increasingly drier conditions, might lose its current competitive advantage in these Mediterranean holm oak forests.     

Tissue-water relations of two co-occurring evergreen Mediterranean species in response to seasonal and experimental drought conditions

Tissue-water relations were used to characterize the responses of two Mediterranean co-occurring woody species (Quercus ilex L. and Phillyrea latifolia L.) to seasonal and experimental drought conditions. Soil water availability was reduced 15% by partially excluding rain throughfall and lateral flow (water runoff). Seasonal and experimental drought elicited physiological and morphological adaptations other than osmotic adjustment: both species showed large increases in cell-wall elasticity and decreased saturated-to-dry-mass ratio. Increased elasticity (lower elastic modulus) resulted in concurrent decreases in relative water content at turgor loss. In addition, P. latifolia showed significant increases in apoplastic water fraction. Decreased saturated-to-dry-mass ratio and increased apoplastic water fraction were accompanied by an increased range of turgor maintenance, which indicates that leaf sclerophyllous traits might be advantageous in drier scenarios. In contrast, the degree of sclerophylly (as assessed by the leaf mass-to-area ratio) was not related to tissue elasticity. An 15% reduction in soil water availability resulted in significant reductions in diameter growth when compared to control plants in both species. Moreover, although P. latifolia underwent larger changes in tissue water-related traits than Q. ilex in response to decreasing water availability, growth was more sensitive to water stress in P. latifolia than in Q. ilex. Differences in diameter growth between species might be partially linked to the effects of cell-wall elasticity and turgor pressure on growth, since Q. ilex showed higher tissue elasticity and higher intrinsic tolerance to water deficit (as indicated by lower relative water content at turgor loss) than P. latifolia.     

Electrophoretic Analysis of Genetic Variation within and between Populations of Quercus cerris,Q. pubescens,Q. petraea and Q. robur (Fagaceae) from Eastern Austria

Allozyme variation at 14 loci was studied electrophoretically in 19 population samples of Quercus cerris, Q. pubescens, Q. petraea, and Q. robur. Genetic variation, measured as mean heterozygosity, was found to be high within populations but low among populations. A significant deficit of heterozygotes was observed in most of the populations of Q. pubescens, Q. petraea, and Q. robur. At the species level, Q. cerris (sect. Cerris) appears to be clearly separated from the rest (sect. Quercus). Q. pubescens, Q. petraea, and Q. robur form a cluster of closely-related species. The degree of genetic differentiation among these species is low, i.e. in the range normally found among con-specific populations. Nevertheless, allozyme data allow the elaboration of a dendrogram which is in reasonable accordance with the taxonomic classification, but also supports the importance of hybridization and introgression. This is also underlined by the fact that the allelic differentiation at the Got-2 locus corresponds with the phenotypic classification (petraea-like, hybrids, and robur-like) in samples from mixed populations.     

Long-term radial growth and climate-growth relationships of Quercus petraea (Matt.) Liebl. and Quercus cerris L. in a xeric low elevation site from Hungary

Sessile oak (Quercus petraea [Matt.] Liebl.) and Turkey oak (Quercus cerris L.) dominated mixed forests are common in low montane and hilly regions in Hungary. Here, we aimed to describe the long-term pattern and climatic responses of the radial growth of Q. petraea and Q. cerris in a xeric low-elevation forest, using retrospective tree-ring analysis for the period 1910–2019. We performed separate analyses with time series of full tree-ring (TRW), earlywood (EW) and latewood (LW) widths. Our results showed that the radial growth of the two species was largely synchronous over time, but became transiently divergent for a 20-year period after a drought in 1968, due to the greater-than-expected growth of Q. cerris and the supressed growth of Q. petraea. Precipitation was the major growth-limiting factor for both species, with a strong positive influence on LW particularly during the current early growing season (March-June), on EW in the previous late summer (August-September) and in the current early spring (March), and on all tree-ring traits in the previous December. The radial growth of both species was negatively related to temperature in the spring (May) and late summer (August) of both current and previous years. The climate-growth relationships showed general instability over time: the most striking temporal change was a gradual shift of positive correlations with precipitation and SPEI during the growing season from spring (March-May) to summer (June-August) since the 1980s over the analysed period. The two species had similarly low growth resistance to droughts in four studied pointer years (1968, 1993, 2002 and 2012), but Q. cerris exhibited a greater capacity to recover over the four post-drought years, and thus higher growth resilience, particularly after the drought of 1968. Our results contribute to the better understanding of the role of climate variability and droughts in the growth of the two co-existing species in transitional locations between closed forests and forest-steppes.     

Sclerophylly in Qualea Parviflora (Vochysiaceae): Influence of Herbivory, Mineral Nutrients, and Water Status

Qualea parviflora Mart. (Vochysiaceae) is a deciduous tree, commonly observed in campo sujo, cerrado sensu stricto and cerradão vegetation types in Brazilian cerrado (savannas). In this study we investigated herbivory, nutritional, and water status effects on leaf sclerophylly of Q. parviflora. Twenty fully expanded leaves were taken from 10 plants in each vegetation type four times a year. Mean leaf concentration of N, P, K, Ca, C, Al, Si, and percentage of total phenols, herbivory and tannins were measured on a plant basis. Leaf specific mass (LSM) (g m^?2), a sclerophylly index, and pre-dawn leaf water potential (MPa) were also recorded. Soil samples below each tree were collected to quantify N–NO₃, N–NH₄, P, K, Mn, soil moisture, organic matter, Si, and Al. Qualea parviflora showed a LSM from 69 to 202 g m^?2 and leaves were younger and less sclerophyllous in November (beginning of rainy season). Q. parviflora inhabiting the cerradão had leaves with higher concentration of nutrients and lower sclerophylly while trees in campo sujo and cerrado sensu stricto did not show significant differences in leaf sclerophylly. The concentrations of N, P, K and tannins had an inverse relationship with leaf age. Concentration of phenols, Al, C, Ca, Si, C/N and Ca/K increased with leaf age. The concentrations of P and Ca/K ratio in leaves explained 60% of variation observed in leaf sclerophylly. We did not find any significant relationship between the level of sclerophylly and water potential or herbivory. Our results corroborate the hypothesis that predicts lower concentrations of essential macronutrients would be the main factors influencing higher sclerophylly in leaves of Q. parviflora plants in Cerrado.     

Caterpillar (Lepidoptera) communities on European Turkey oak (Quercus cerris) in Malé Karpaty Mts (SW Slovakia)

Between 2000–2002, the structure of communities of lepidopteran larvae was studied in leaf bearing crowns of Quercus cerris in the central and northern part of the Malé Karpaty Mts (SW Slovakia). Caterpillars were collected using the beating method in four study plots. In total, 58 species were found. The families Geometridae, Noctuidae and Tortricidae comprised the highest number of species found. The family Geometridae comprised the highest number of pests. The most abundant species for individual plots were Lymantria dispar, Operophtera brumata, Ypsolopha alpella and Cyclophora ruficiliaria. Most of the recorded species belonged to the trophic group of generalists (39 species). Shannon-Wiener’s diversity index and Pielou’s equitability (evenness) value indicated there were marked differences between the Horny háj study plot (an insular forest with ants as the predators of caterpillars) and other plots. The main ecological gradient along DCA-1 related to the host specificity of caterpillars and consisted of three groups: (a) polyphagous species; (b) specialist species feeding chiefly on oaks or exclusively on oaks and (c) species preferring some oak species, mainly Q. cerris. The fragmentation of growth was identified along DCA-2.     

Anatomical studies of branchlet abscission related to crown modification in Quercus cerris L.

The basic anatomy of lateral twig insertion onto the main branch in both healthy and damaged Quercus cerris L. trees was studied. An abscission zone is always present: in healthy trees it is formed by a smaller number of cell layers than in damaged ones, where it is more evident with many layers of cells. Cells of the abscission zone are roundish, with many intercellular spaces between them; cell walls are thin, non-lignified and without secondary walls. No starch was found in cells of the abscission zone, where, instead, a few scattered calcium oxalate druses are seen.     

7年穿透雨减少对锐齿槲栎光合固碳及生物量碳储量的影响

气候变化背景下不断加剧的干旱事件对树木的生长及碳积累产生显著影响。然而,树木光合固碳能力及生物量碳储量对相对长期干旱的连续响应机制的研究仍然有限。选择70年生的天然锐齿槲栎(Quercus aliena var.acuteserrata)林,探究长期模拟穿透雨减少对锐齿槲栎光合固碳潜力和生物量碳储量的影响。研究结果表明,连续7年的穿透雨减少处理显著降低了锐齿槲栎的光合固碳能力,其叶片净光合速率(A)、最大羧化速率(V_cmax)、最大电子传递速率(J_max)、最大光化学效率(F_v/F_m)均明显降低,且穿透雨减少处理增强了A与气孔导度(g_s)、J_max、F_v/F_m之间的相关性。在适应长期干旱过程中,锐齿槲栎通过增加比叶面积(SLA)、叶片栅栏组织与海绵组织的比值、气孔密度等叶片形态及结构特性变化,降低冠层叶面积(LAI)指数和蒸腾水分散失及提高水分利用效率(WUE)缓解和适应干旱胁迫的不利影响。但是,长期穿透雨减少仍...     

Field-simulated droughts affect elemental leaf stoichiometry in Mediterranean forests and shrublands

This study evaluated the change induced by the year season and by experimentally induced drought on foliar element stoichiometry of the predominant woody species (Quercus ilex and Erica multiflora) in two Mediterranean ecosystems, a forest and a shrubland. This study is based in two long-term (11 yr) field experiments that simulated drought throughout the annual cycle.The effects of experimental droughts were significant but weaker than the changes produced by ontogeny and seasonality. Leaf N and P concentrations were higher in spring (the main growing season) in E. multiflora and, in Q. ilex in autumn (a period of additional growth). Leaf N:P ratios were lower in spring. In Q. ilex, the highest leaf K concentrations and leaf K:P ratios, and the lowest leaf C:K and N:K ratios, occurred in summer, the season when water stress was greatest. In E. multiflora, leaf K concentrations and K:P ratios were highest, and leaf C:K and N:K ratios were lowest in the plants from the drought-treated plots.The plant capacity to change K concentrations in response to seasonality and to drought is at least as great as the capacity to change N and P concentrations. The results underscore the importance of K and its stoichiometry relative to C, N and P in dry environments. These results indicate first, that N:P ratio shifts are not uniquely related to growth rate in Mediterranean plants but also to drought, and second, that there is a need to take into account K in ecological stoichiometry studies of terrestrial plants.     

Interspecific Differences of Leaf Gas Exchange and Water Relations of Three Evergreen Mediterranean Shrub Species

Leaf gas exchange and plant water relations of three co-occurring evergreen Mediterranean shrubs species, Quercus ilex L. and Phillyrea latifolia L. (typical evergreen sclerophyllous shrubs) and Cistus incanus L. (a drought semi-deciduous shrub), were investigated in order to evaluate possible differences in their adaptive strategies, in particular with respect to drought stress. C. incanus showed the highest annual rate of net photosynthetic rate (P _N) and stomatal conductance (g _s) decreasing by 67 and 69 %, respectively, in summer. P. latifolia and Q. ilex showed lower annual maximum P _N and g _s, although P _N was less lowered in summer (40 and 37 %, respectively). P. latifolia reached the lowest midday leaf water potential (₁) during the drought period (–3.54±0.36 MPa), 11 % lower than in C. incanus and 19 % lower than in Q. ilex. Leaf relative water content (RWC) showed the same trend as ₁. C. incanus showed the lowest RWC values during the drought period (60 %) while they were never below 76 % in P. latifolia and Q. ilex; moreover C. incanus showed the lowest recovery of ₁ at sunset. Hence the studied species are well adapted to the prevailing environment in Mediterranean climate areas, but they show different adaptive strategies that may be useful for their co-occurrence in the same habitat. However, Q. ilex and P. latifolia by their water use strategy seem to be less sensitive to drought stress than C. incanus.     

Leaf area index (LAI) map of a protected area within the caldera of Vico Lake (Italy)

ABSTRACT

Structural traits of the vegetation types and plantations occurring in a protected area within the caldera of Vico Lake (Italy) were analysed. There were significant correlations among structural traits, at leaf and stand level. Leaf area index (LAI) and specific leaf area (SLA) were the most significantly correlated traits. LAI rose according to stand plant density, tree size and SLA; the highest LAI value monitored in the Fagus sylvatica L. forest was justified by the largest tree size (28.9±2.8 m height and 53±15 cm diameter) and the highest SLA (212±23 cm² g^-1). The main traits determining the variations in leaf structure among species were analysed by Principal Component Analysis (PCA). The LAI values were used to realise a map allowing us to delimit high LAI values (4.1–5.0), corresponding to the F. sylvatica forest and to the F. sylvatica forest with the sporadic presence of Quercus cerris L. and Castanea sativa Miller, mean LAI values (classes 3.1–4.0) corresponding to Corylus avellana L. plantations and to the Phragmites australis (Cav.) Trin. vegetation type, low LAI values (classes 2.6–3.0) corresponding to Q. cerris forests and C. sativa plantations.