The complete mitochondrial genome of Castanopsis carlesii and Castanea henryi reveals the rearrangement and size differences of mitochondrial DNA molecules.

BACKGROUND: Castanopsis carlesii is a dominant tree species in subtropical evergreen broad-leaved forests and holds significant ecological value. It serves as an excellent timber tree species and raw material for cultivating edible fungi. Henry Chinquapin (Castanea henryi) wood is known for its hardness and resistance to water and moisture, making it an exceptional timber species. Additionally, its fruit has a sweet and fruity taste, making it a valuable food source. However, the mitogenomes of these species have not been previously reported. To gain a better understanding of them, this study successfully assembled high-quality mitogenomes of C. carlesii and Ca. henryi for the first time. RESULTS: Our research reveals that the mitochondrial DNA (mtDNA) of C. carlesii exhibits a unique multi-branched conformation, while Ca. henryi primarily exists in the form of two independent molecules that can be further divided into three independent molecules through one pair of long repetitive sequences. The size of the mitogenomes of C. carlesii and Ca. henryi are 592,702 bp and 379,929 bp respectively, which are currently the largest and smallest Fagaceae mitogenomes recorded thus far. The primary factor influencing mitogenome size is dispersed repeats. Comparison with published mitogenomes from closely related species highlights differences in size, gene loss patterns, codon usage preferences, repetitive sequences, as well as mitochondrial plastid DNA segments (MTPTs). CONCLUSIONS: Our study enhances the understanding of mitogenome structure and evolution in Fagaceae, laying a crucial foundation for future research on cell respiration, disease resistance, and other traits in this family.

The effect of local habitat and spatial connectivity on urban seed predation.

PREMISE: During the last centuries, the area covered by urban landscapes is increasing all over the world. Urbanization can change local habitats and decrease connectivity among these habitats, with important consequences for species interactions. While several studies have found a major imprint of urbanization on plant-insect interactions, the effects of urbanization on seed predation remain largely unexplored. METHODS: We investigated the relative impact of sunlight exposure, leaf litter, and spatial connectivity on predation by moth and weevil larvae on acorns of the pedunculate oak across an urban landscape during 2018 and 2020. We also examined whether infestations by moths and weevils were independent of each other. RESULTS: While seed predation varied strongly among trees, seed predation was not related to differences in sunlight exposure, leaf litter, or spatial connectivity. Seed predation by moths and weevils was negatively correlated at the level of individual acorns in 2018, but positively correlated at the acorn and the tree level in 2020. CONCLUSIONS: Our study sets the baseline expectation that urban seed predators are unaffected by differences in sunlight exposure, leaf litter, and spatial connectivity. Overall, our findings suggest that the impact of local and spatial factors on insects within an urban context may depend on the species guild. Understanding the impact of local and spatial factors on biodiversity, food web structure, and ecosystem functioning can provide valuable insights for urban planning and management strategies aimed at promoting urban insect diversity.

Harmful self-pollination drives gynodioecy in European chestnut, a self-incompatible tree.

PREMISE: Gynodioecy is a rare sexual system in which two genders (sensu Lloyd, 1980), cosexuals and females, coexist. To survive, female plants must compensate for their lack of siring capacity and male attractiveness. In European chestnut (Castanea sativa), an outcrossing tree, self-pollination reduces fruit set in cosexual individuals because of late-acting self-incompatibility and early inbreeding depression. Could this negative sexual interaction explain the presence of females in this species? METHODS: We studied gender variation in wild populations of European chestnut. In addition, we compared fruit set (the proportion of flowers giving fruits) and other key female fitness components as well as reproductive allocation between genders. We then performed emasculation experiments in cosexual trees, by removing nectar-producing fertile male inflorescences. We also removed sterile but nectar-producing male inflorescences from female trees, as a control. RESULTS: We found a highly variable proportion of male-sterile individuals in the wild in European chestnut. In the experimental plot, trees from each gender had similar size, flower density, and burr set, but different fruit set. Removing nectar-producing male inflorescences from branches or entire trees increased fruit set in cosexual but not in female trees. CONCLUSIONS: These results show that self-pollination impairs fruit set in cosexual trees. Female trees avoid these problems as they do not produce pollen but continue to attract pollinators thanks to their rewarding male-sterile inflorescences, resulting in a much higher fruit set than in cosexuals. This demonstrates that even outcrossed plants can benefit from the cessation of self-pollination, to the point that unisexuality can evolve.

Leaf functional traits and ecological niche of Fagus grandifolia and Oreomunnea mexicana in natural forests and plantings as a proxy of climate change.

PREMISE: Functional traits reflect species' responses to environmental variation and the breadth of their ecological niches. Fagus grandifolia and Oreomunnea mexicana have restricted distribution in upper montane cloud forests (1700-2000 m a.s.l.) in Mexico. These species were introduced into plantings at lower elevations (1200-1600 m a.s.l.) that have climates predicted for montane forests in 2050 and 2070. The aim was to relate morphological leaf traits to the ecological niche structure of each species. METHODS: Leaf functional traits (leaf area, specific leaf area [SLA], thickness, and toughness) were analyzed in forests and plantings. Atmospheric circulation models and representative concentration pathways (RCPs: 2.6, 4.5, 8.5) were used to assess future climate conditions. Trait-niche relationships were analyzed by measuring the Mahalanobis distance (MD) from the forests and the plantings to the ecological niche centroid (ENC). RESULTS: For both species, leaf area and SLA were higher and toughness lower in plantings at lower elevation relative to those in higher-elevation forests, and thickness was similar. Leaf traits varied with distance from sites to the ENC. Forests and plantings have different environmental locations regarding the ENC, but forests are closer (MD 0.34-0.58) than plantings (MD 0.50-0.70) for both species. CONCLUSIONS: Elevation as a proxy for expected future climate conditions influenced the functional traits of both species, and trait patterns related to the structure of their ecological niches were consistent. The use of distances to the ENC is a promising approach to explore variability in species' functional traits and phenotypic responses in optimal versus marginal environmental conditions.

First report of Bretziella fagacearum infecting chestnut in Michigan.

In the summer of 2021, a 20-year-old 'Colossal' (Castanea sativa × C. crenata hybrid) tree in a commercial chestnut orchard in northwest Michigan suddenly declined. Until 2023, an additional 26 adjacent trees declined, suggesting the occurrence of root-graft transmission of the pathogen. The initial wilting of leaves progressed to complete tree death in about 10 days. Symptoms included wilting, and bronzing, followed by tanning starting at leaf apex and margins, with significant defoliation. Sometimes black-to-brown streaks of discoloration appear in the sapwood, with no signs of mycelial mat production on dead trees. Branches from symptomatic trees in two different areas of the orchard were submitted to Plant and Pest Diagnostics at Michigan State University. Bretziella fagacearum (Bretz) Z.W. de Beer, Marinc., T.A. Duong & M.J. Wingf. was detected in both samples using nested PCR (Wu et al. 2011) and qPCR (Bourgault et al. 2022). The products of the nested PCR were sequenced (GenBank accession nos. OR522695-OR522696) and BLASTn search results showed 100% identity to an ex-type strain of B. fagacearum (MH865866). Surface-sterilized discolored sapwood chips were plated on acidified potato dextrose agar (aPDA). Bretziella fagacearum was consistently recovered; colony and endoconidia morphology aligned with the description of the pathogen (De Beer et al. 2017). A pure culture (BF277) was obtained for inoculation experiments. To confirm pathogenicity, 10 'Colossal' chestnut seedlings (average stem diameter of 9 mm) were inoculated in the greenhouse with a 14-day old culture of BF277. Using a conical drill bit, two 0.4 mm diameter holes were drilled, one was 5 cm above the soil line at a 45° angle and the other was on the opposite side of the stem at least 10 cm above the soil line. A 50-µl conidial suspension (1 × 107 conidia per ml) was applied and the holes were sealed with Parafilm. Five 'Colossal' seedlings were inoculated with sterile water. Leaf epinasty with bent petioles was observed 14 days later. Leaf wilting and necrosis similar to natural infection in the orchard were observed at 24 and 34 days after inoculation, respectively. Water-inoculated control plants showed no symptoms. Bretziella fagacearum was reisolated from symptomatic plants by surface sterilizing leaf petioles with 75% ethanol (30 s), followed by 10% (v/v) bleach (1 min), and two rinses with sterile deionized water (>1 min). Petiole pieces (~1 cm) were plated on aPDA. The pathogen was reisolated from six symptomatic plants and detected using qPCR in the remaining four seedlings. Bretziella fagacearum was not detected in control plants. The identity of the recovered fungus was confirmed following the amplification of the internal transcribed spacer (ITS) from extracted genomic DNA, as described in Chahal et al. 2022. The resulting PCR product was sequenced and assembled into a consensus sequence using Geneious Prime. The consensus sequence (accession no. OR515809) revealed 100% identity to the ex-type of B. fagacearum (KU042044). This is the first record of B. fagacearum infecting chestnut trees in Michigan. Previously, B. fagacearum has been reported infecting Chinese chestnut (C. mollissima) in Missouri (Bretz and Long, 1950). Oak wilt is widely distributed in Michigan and is the predominant disease afflicting red oaks in the Midwestern U.S. Consequently, constant vigilance and monitoring are essential in chestnut orchards to promptly detect and effectively manage potential infections.

An integrative framework reveals widespread gene flow during the early radiation of oaks and relatives in Quercoideae (Fagaceae).

Although the frequency of ancient hybridization across the Tree of Life is greater than previously thought, little work has been devoted to uncovering the extent, timeline, and geographic and ecological context of ancient hybridization. Using an expansive new dataset of nuclear and chloroplast DNA sequences, we conducted a multifaceted phylogenomic investigation to identify ancient reticulation in the early evolution of oaks (Quercus). We document extensive nuclear gene tree and cytonuclear discordance among major lineages of Quercus and relatives in Quercoideae. Our analyses recovered clear signatures of gene flow against a backdrop of rampant incomplete lineage sorting, with gene flow most prevalent among major lineages of Quercus and relatives in Quercoideae during their initial radiation, dated to the Early-Middle Eocene. Ancestral reconstructions including fossils suggest ancestors of Castanea + Castanopsis, Lithocarpus, and the Old World oak clade probably co-occurred in North America and Eurasia, while the ancestors of Chrysolepis, Notholithocarpus, and the New World oak clade co-occurred in North America, offering ample opportunity for hybridization in each region. Our study shows that hybridization-perhaps in the form of ancient syngameons like those seen today-has been a common and important process throughout the evolutionary history of oaks and their relatives. Concomitantly, this study provides a methodological framework for detecting ancient hybridization in other groups.

Revisiting the pericarp as a barrier restricting water entry/loss from cotyledons and embryonic axis of temperate desiccation-sensitive Quercus acorns.

MAIN CONCLUSIONS: Fully mature acorns of Quercus variabilis, Q. aliena, Q. mongolica, and Q. glandulifera are desiccation-sensitive. X-ray computer tomography showed that cotyledons shrink during drying, but embryos are protected. Information available on recalcitrant acorns of tropical and sub-tropical species of Quercus suggests that an impermeable pericarp, which limits the entry and loss of water only through the hilum (scar), is the underlying mechanism that prevents drying of the embryo axis following dispersal until the germination season. However, there is a lack of consensus supporting this proposition across species, and it is not well understood if such mechanisms occur in temperate Quercus species. This study investigated the significance of the acorn pericarp for temperate oak species and presents an ecological framework based on the post-dispersal climatic conditions. Using Quercus variabilis, Q. aliena, Q. mongolica, and Q. glandulifera acorns, the relationship between moisture content (MC) and germination was established, and X-ray computed tomography (X-ray CT) was used to understand the internal structural changes of cotyledons and embryonic axis occurring during desiccation. Water entry and exit routes through the scar, pericarp and apex were determined by imbibition and drying experiments. Climatic data and acorn morphological characteristics and germination were subjected to a principal component analysis (PCA). Freshly dispersed acorns of all species had a moisture content (MC) above 35% fresh weight (FW) basis, but drying to 15-10% MC resulted in complete loss of viability, implying recalcitrance behaviour. X-ray CT images suggested that the pericarp offers some protection to cotyledons and embryonic axis during desiccation, but it is contingent on MC. Extensive drying to a low MC with the scar and apex covered with vaseline resulted in internal tissues shrinkage, corresponding with viability loss. Water could enter or exit through the pericarp, albeit at a much slower rate than through the scar. A combination of factors including acorn anatomy, moisture content at the time of dispersal, microhabitat, the position of acorns in the soil prevent embryo desiccation below the critical MC and thus promotes survival of acorns on/in the soil during winter in temperate regions. Pericarp anatomy, to some extent, prevents excessive drying of the embryonic axis by slowing water movement, but prolonged drying or predatory pressure could result in pericarp cracks, favouring the absorption of water during sporadic rain. In the latter case, the survival of acorns possibly depends extensively on the continuous erratic rainfall, i.e. continuous wet-dry cycle, but in-situ experiments are yet to be performed to test this hypothesis.

Characterization of pollen tube development in distant hybridization of Chinese cork oak (Quercus variabilis L.).

MAIN CONCLUSION: This work mainly found that the stigma and style of Q. variabilis did not completely lose the specific recognition towards heterologous pollen, a fact which is different from previous studies. Quercus is the foundation species in the Northern Hemisphere, with extreme prevalence for interspecific hybridization. It is not yet entirely understood whether or how the pollen tube-female tissue interaction contributes to the "extensive hybridization" in oaks. Pollen storage conditions correlate with distant hybridization. We conducted hybridization experiments with Q. variabilis as female and Q. variabilis and Q. mongolica as male parents. And the differences in pollen tube (PT) development between intra- and distant interspecific hybridization were studied by fluorescence microscopy and scanning electron microscopy (SEM). Our results showed that -20 °C allowed pollen of both species to maintain some viability. Both Q. variabilis and Q. mongolica pollen germinated profusely on the stigmas. SEM results indicated that in the intraspecific hybridization, Q. variabilis pollen started to germinate at 6 h after pollination (hap), PTs elongated significantly at 12 hap, and entered the stigma at 24 hap. By contrast, Q. mongolica pollen germinated at 15 hap, and the PTs entered the stigma at 27 hap. By fluorescence microscopical studies it was observed that some PTs of Q. variabilis gathered at the style-joining at 96 hap, unlike the Q. mongolica which reached the style junction at 144 hap. The above results indicate that the abundant germination of heterologous pollen (HP) on the stigma and the "Feeble specificity recognition" of the stigma and transmitting tract to HP may create opportunities for the "extensive hybridization" of oaks. This work provides a sexual developmental reference for clarifying the causes of Quercus "extensive hybridization".

Nuclear and chloroplast DNA phylogeography reveals high genetic diversity and postglacial range expansion in Quercus mexicana.

PREMISE: Phylogeographical studies are fundamental for understanding factors that influence the spatial distribution of genetic lineages within species. Population expansions and contractions, distribution shifts, and climate changes are among the most important factors shaping the genetic compositions of populations. METHODS: We investigated the phylogeography of an endemic oak, Quercus mexicana (Fagaceae), which has a restricted distribution in northeastern Mexico along the Sierra Madre Oriental and adjacent areas. Nuclear and chloroplast DNA microsatellite markers were used to describe the genetic diversity and structure of 39 populations of Q. mexicana along its entire distribution area. We tested whether population expansion or contraction events influenced the genetic diversity and structure of the species. We also modeled the historical distributional range of Q. mexicana (for the Mid Holocene, the Last Glacial Maximum, and the Last Interglacial) to estimate the extent to which climate fluctuations have impacted the distribution of this oak species. RESULTS: Our results revealed high genetic diversity and low genetic structure in Q. mexicana populations. Ecological niche models suggested historical fluctuations in the distributional range of Q. mexicana. Historical range changes, gene flow, and physical barriers seem to have played an important role in shaping the phylogeographic structure of Q. mexicana. CONCLUSIONS: Our study indicates that the genetic structure of Q. mexicana may have been the result of responses of oak trees not only to heterogeneous environments present in the Sierra Madre Oriental and adjacent areas, but also to elevational and latitudinal shifts in response to climate changes in the past.

Adaptive function of duodichogamy: Why do chestnut trees have two pollen emission phases?

PREMISE: Intersexual mating facilitation in flowering plants has been largely underexplored. Duodichogamy is a rare flowering system in which individual plants flower in the sequence male-female-male. We studied the adaptive advantages of this flowering system using chestnuts (Castanea spp., Fagaceae) as models. These insect-pollinated trees produce many unisexual male catkins responsible for a first staminate phase and a few bisexual catkins responsible for a second staminate phase. We hypothesized that duodichogamy increases female mating success by facilitating pollen deposition on stigmas of the rewardless female flowers through their proximity with attractive male flowers responsible for the minor staminate phase. METHODS: We monitored insect visits to 11 chestnut trees during the entire flowering period and explored reproductive traits of all known duodichogamous species using published evidence. RESULTS: In chestnuts, insects visited trees more frequently during the first staminate phase but visited female flowers more frequently during the second staminate phase. All 21 animal-pollinated duodichogamous species identified are mass-flowering woody plants at high risk of self-pollination. In 20 of 21 cases, gynoecia (female flower parts) are located close to androecia (male flower parts), typically those responsible for the second minor staminate phase, whereas androecia are often distant from gynoecia. CONCLUSIONS: Our results suggest that duodichogamy increases female mating success by facilitating pollen deposition on stigmas by means of the attractiveness of the associated male flowers while effectively limiting self-pollination.

The Fungal Pathogen Gnomoniopsis castaneae Induces Damaging Cankers in Multiple Domestic Fagaceae Species.

Gnomoniopsis castaneae is internationally recognized as a destructive pathogen of chestnut species. Primarily associated with nut rot, it has also been associated with branch and stem cankers of chestnut and as an endophyte of multiple additional hardwood species. The present study evaluated implications of the recently reported United States presence of the pathogen for domestic Fagaceae species. Stem inoculation assays of Castanea dentata, C. mollissima, C. dentata × C. mollissima, and Quercus rubra (red oak) seedlings were utilized to examine the cankering ability of a regional isolate of the pathogen. The pathogen induced damaging cankers in all assessed species and significant stem girdling in all chestnut species. No previous study has associated the pathogen with damaging infection in Quercus species, and its presence in the United States has the potential to compound ongoing chestnut recovery programs and oak regeneration problems within forest systems.

Cryphonectria carpinicola discovered in Japan: first report of the sexual state on Carpinus tree.

Cryphonectria carpinicola is an ascomycetous fungus that has been regularly found in its asexual form on European hornbeam (Carpinus betulus) in Europe over the past two decades. Here we describe the discovery of C. carpinicola in Japan and report for the first time its sexual state on Carpinus species. No symptomatic trees were observed, but stromata were found saprotrophically on broken branches of Carpinus species on the forest floor. The sexual structures of C. carpinicola resembled that of other Cryphonectria species and strongly resembled those of the closely related species C. radicalis. A phylogenetic tree based on the internal transcribed spacer sequences showed monophyly for the Japanese and European isolates of C. carpinicola. Further studies on the distribution and host range of C. carpinicola in Japan and on the life history strategies of this fungus are needed.

Evolution of Castanea in North America: restriction-site-associated DNA sequencing and ecological modeling reveal a history of radiation, range shifts, and disease.

PREMISE: Although chestnuts and chinquapins are some of the best known and most widely loved of any plants in North America, relatively little genomic sequencing has been done, and much is still unknown about their evolution. METHODS: We used double-digest restriction-site-associated DNA (ddRAD) sequencing data to infer the species-level phylogeny for Castanea and assess the phylogeography of the North American species using samples collected from populations that span the full extent of the species' ranges. We also constructed species distribution models using digitized herbarium specimens and observational data from field surveys. RESULTS: We identified strong population structure within Castanea dentata (American chestnut) that reflects a stepwise northern migration since the last glacial maximum. Our species distribution models further confirmed this scenario and matched closely with the Castanea fossil pollen record. We also found significant structure within the Castanea pumila lineage, most notably a genetic cluster that corresponds to the frequently recognized Castanea pumila var. ozarkensis. CONCLUSIONS: The two North American Castanea species have contrasting patterns of population structure, but each is typical of plant phylogeography in North America. Within the C. pumila complex, we found novel genetic structure that provides new insights about C. pumila taxonomy. Our results also identified a series of distinctive populations that will be valuable in ongoing efforts to conserve and restore chestnuts and chinquapins in North America.

Variations in morphological and epidermal features of shade and sun leaves of two species: Quercus bambusifolia and Q. myrsinifolia.

PREMISE: Microclimatic differences between the periphery and the interior of tree crowns result in a variety of adaptive leaf macromorphological and anatomical features. Our research was designed to reveal criteria for sun/shade leaf identification in two species of evergreen oaks, applicable to both modern and fossil leaves. We compared our results with those in other species similarly studied. METHODS: For both Quercus bambusifolia and Q. myrsinifolia (section Cyclobalanopsis), leaves from single mature trees with well-developed crowns were collected in the South China Botanical Garden, Guangzhou, China. We focus on leaf characters often preserved in fossil material. SVGm software was used for macromorphological measurement. Quantitative analyses were performed and box plots generated using R software with IDE Rstudio. Leaf cuticles were prepared using traditional botanical techniques. RESULTS: Principal characters for distinguishing shade and sun leaves in the studied oaks were identified as leaf lamina length to width ratio (L/W), and the degree of development of venation networks. For Q. myrsinifolia, shade and sun leaves differ in tooth morphology and the ratio of toothed lamina length to overall lamina length. The main epidermal characters are ordinary cell size and anticlinal wall outlines. For both species, plasticity within shade leaves exceeds that of sun leaves. CONCLUSIONS: Morphological responses to sun and shade in the examined oaks are similar to those in other plant genera, pointing to useful generalizations for recognizing common foliar polymorphisms that must be taken into account when determining the taxonomic position of both modern and fossil plants.

Adaptive Evolution of Chalcone Isomerase Superfamily in Fagaceae.

Chalcone Isomerase (CHI) catalyzes the biosynthesis of flavonoids and secondary metabolism in plants. Currently, there is no systematic analysis of CHIs gene family in Fagaceae which is available. In this study, twenty-two CHI proteins were identified in five species of the Fagaceae family. The CHI superfamily in Fagaceae can be classified into three subfamilies and five groups using phylogenetic analysis, analysis of physicochemical properties, and structural prediction. Results indicated that serine (Ser) and isoleucine (Ile) residues determine the substrate preferred by active Type I Fagaceae CHI, and the chalcone isomerase-like (CHIL) of Fagaceae had active site residues. Adaptive analysis of CHIs showed that CHIs are subject to selection pressure. The active CHI gene of Fagaceae was located in the cytoplasm, and it had the typical gene structure of CHI and contains four exons. All the twenty-two identified CHIs had the conserved domain motif 3, and the different groups had their own structural characteristics. In the process of fatty acid binding protein (FAP) evolution to CHIL and CHI, the physical and chemical properties of proteins also had significant differences in addition to changes in protein functions.

Ontogenetic scaling of phloem sieve tube anatomy and hydraulic resistance with tree height in Quercus rubra.

PREMISE: The dimensions of phloem sieve elements have been shown to vary as a function of tree height, decreasing hydraulic resistance as the transport pathway lengthens. However, little is known about ontogenetic patterns of sieve element scaling. Here we examine within a single species (Quercus rubra) how decreases in hydraulic resistance with distance from the plant apex are mediated by overall plant size. METHODS: We sampled and imaged phloem tissue at multiple heights along the main stem and in the live crown of four size classes of trees using fluorescence and scanning electron microscopy. Sieve element length and radius, the number of sieve areas per compound plate, pore number, and pore radius were used to calculate total hydraulic resistance at each sampling location. RESULTS: Sieve element length varied with tree size, while sieve element radius, sieve pore radius, and the number of sieve areas per compound plate varied with sampling position. When data from all size classes were aggregated, all four variables followed a power-law trend with distance from the top of the tree. The net effect of these ontogenetic scalings was to make total hydraulic sieve tube resistance independent of tree height from 0.5 to over 20 m. CONCLUSIONS: Sieve element development responded to two pieces of information, tree size and distance from the apex, in a manner that conserved total sieve tube resistance across size classes. A further differentiated response between the phloem in the live crown and in the main stem is also suggested.

Greater phylogenetic distance from native oaks predicts escape from insect leaf herbivores by non-native oak saplings.

PREMISE: Non-native plant species have been hypothesized to experience lower herbivory in novel environments as a function of their phylogenetic distance from native plant species. Although recent work has found support for this prediction, the plant traits responsible for such patterns have been largely overlooked. METHODS: In a common garden experiment in northwestern Spain, we tested whether oak species (Quercus spp.) not native to this region that are phylogenetically more distantly related to native species exhibit less insect leaf herbivory. In addition, we also investigated plant traits potentially correlated with any such effect of phylogenetic distance. RESULTS: As expected, phylogenetic distance from native species negatively predicted insect leaf herbivory on non-native oaks. In addition, we found that the leaf traits, namely phosphorus and condensed tannins, were significantly associated with herbivory, suggesting that they are associated with the effect of phylogenetic distance on leaf herbivory on non-native oak species. CONCLUSIONS: This study contributes to a better understanding of how evolutionary relationships (relatedness) between native and non-native plant species determine the latter's success in novel environments via locally shared enemies, and encourages more work investigating the plant traits that mediate the effects of phylogenetic distance on enemy escape.

Parallel increases in insect herbivory and defenses with increasing elevation for both saplings and adult trees of oak (Quercus) species.

PREMISE: Herbivory is predicted to increase toward warmer and more stable climates found at lower elevations, and this increase should select for higher plant defenses. Still, a number of recent studies have reported either no evidence of such gradients or reverse patterns. One source of inconsistency may be that plant ontogenetic variation is usually not accounted for and may influence levels of plant defenses and herbivory. METHODS: We tested for elevational gradients in insect leaf herbivory and leaf traits putatively associated with herbivore resistance across eight oak (Quercus, Fagaceae) species and compared these patterns for saplings and adult trees. To this end, we surveyed insect leaf herbivory and leaf traits (phenolic compounds, toughness and nutrients) in naturally occurring populations of each oak species at low-, mid- or high-elevation sites throughout the Iberian Peninsula. RESULTS: Leaf herbivory and chemical defenses (lignins) were unexpectedly higher at mid- and high-elevation sites than at low-elevation sites. In addition, leaf chemical defenses (lignins and condensed tannins) were higher for saplings than adult trees, whereas herbivory did not significantly differ between ontogenetic stages. Overall, elevational variation in herbivory and plant chemical defenses were consistent across ontogenetic stages (i.e., elevational gradients were not contingent upon tree ontogeny), and herbivory and leaf traits were not associated across elevations. CONCLUSIONS: These findings suggest disassociated patterns of elevational variation in herbivory and leaf traits, which, in turn, are independent of plant ontogenetic stage.

Biomechanical control of beech pole verticality (Fagus sylvatica) before and after thinning: theoretical modelling and ground-truth data using terrestrial LiDAR.

PREMISE OF THE STUDY: Thinning is a frequent disturbance in managed forests, especially to increase radial growth. Due to buckling and bending risk associated with height and mass growth, tree verticality is strongly constrained in slender trees growing in dense forests and poor light conditions. Tree verticality is controlled by uprighting movements implemented from local curvatures induced by wood maturation stresses and/or eccentric radial growth. This study presents the first attempt to compare the real uprighting movements in mature trees using a theoretical model of posture control. METHODS: Stem lean and curvature were measured by Terrestrial LiDAR Scanner (TLS) technology before and 6 years after thinning and compared to unthinned control poles. Measures for several tree and wood traits were pooled together to implement a widely used biomechanical model of tree posture control. Changes in observed stem lean were then compared with the model predictions, and discrepancies were reviewed. KEY RESULTS: Even under a highly constrained environment, most control poles were able to counterbalance gravitational curvature and avoid sagging. Thinning stimulated uprighting movements. The theoretical uprighting curvature rate increased just after thinning, then slowed after 2 years, likely due to the stem diameter increase. The biomechanical model overestimated the magnitude of uprighting. CONCLUSIONS: Most suppressed beech poles maintain a constant lean angle, and uprighting movements occur after thinning, indicating that stem lean is plastic in response to light conditions. Acclimation of posture control to other changes in growth condition should be investigated, and lean angles should be measured in forest inventories as an indicator of future wood quality.

Synchrony in fall leaf drop: chlorophyll degradation, color change, and abscission layer formation in three temperate deciduous tree species.

PREMISE OF THE STUDY: Deciduous tree species remove some nutrients from their leaves during fall leaf senescence through retranslocation. Retranslocation impacts the timeline of leaf fall, amount of active chlorophyll, and overall leaf nitrogen content as fall color change occurs. Our objective was to identify interspecific differences in the timing of abscission layer formation, leaf color change, and the level of chlorophyll degradation of young trees during fall senescence. METHODS: Leaf relative chlorophyll content for three tree species was measured during fall 2015 by a greenness meter. These measurements were calibrated for each species through spectrophotometric determination of leaf chlorophyll concentration. Abscission layer formation was tracked using light microscopy of sampled leaves. Excised leaves were photographed on a flat white surface to track species leaf color through time. KEY RESULTS: All three species had different chlorophyll declination rates throughout the fall season. The maple species started with less chlorophyll and began abscission layer formation earlier. The other two species had a similar starting chlorophyll level and onset timing of abscission layer formation. Visible leaf color change was not associated with a threshold in either chlorophyll degradation or abscission layer formation across species. CONCLUSIONS: Maple species degraded less chlorophyll on average, in the fall, than did the oak and beech species. The rate of chlorophyll degradation in coordination with abscission layer formation varied by species. Color change was not a good predictor of level of chlorophyll degradation in leaves across species.