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• Vulnerability to cavitation and conductive efficiency depend on xylem anatomy. We tested a large range of structure-function hypotheses, some for the first time, within a single genus to minimize phylogenetic ‘noise' and maximize detection of functionally relevant variation. • This integrative study combined in-depth anatomical observations using light, scanning and transmission electron microscopy of seven Acer taxa, and compared these observations with empirical measures of xylem hydraulics. • Our results reveal a 2 MPa range in species' mean cavitation pressure (MCP). MCP was strongly correlated with intervessel pit structure (membrane thickness and porosity, chamber depth), weakly correlated with pit number per vessel, and not related to pit area per vessel. At the tissue level, there was a strong correlation between MCP and mechanical strength parameters, and some of the first evidence is provided for the functional significance of vessel grouping and thickenings on inner vessel walls. In addition, a strong trade-off was observed between xylem-specific conductivity and MCP. Vessel length and intervessel wall characteristics were implicated in this safety-efficiency trade-off. • Cavitation resistance and hydraulic conductivity in Acer appear to be controlled by a very complex interaction between tissue, vessel network and pit characteristics.

This atlas presents anatomical descriptions of the xylem, bark and pith of 264 species belonging to 69 families. It highlights the anatomical diversity of trees, shrubs, dwarf shrubs, woody lianas and several of the prominent perennial herbs from the Eastern Mediterranean region, with a focus on the island of Cyprus. The island's topography and biogeographic history combine to provide a wide range of habitats and diverse flora including widespread, endemic, and ornamental species. The monograph for each species includes a description of the anatomical structures of the stem and twig xylem and the twig's bark and pith, as well as color micrographs of double-stained sections of each of these plant parts. These entries are accompanied by a photograph and a brief description of the plant including stem wood density, height, habit, flower, leaf and fruit characteristics, and a map showing its geographic and altitudinal distribution in the region. Xylem descriptions follow the IAWA lists of microscopic features for hardwood and softwood identification. For bark and pith descriptions, a new coding system developed by the authors is applied. Lastly, the atlas offers a key for wood identification that was developed to differentiate between groups of species by using a small number of features that are unambiguous and clearly visible. The atlas will be a valuable guide for botanists, ecologists, foresters, archeologists, horticulturists and paleobotanists.

Conifer tree rings are generally composed of large, thin-walled cells of light earlywood followed by narrow, thick-walled cells of dense latewood. Yet, how wood formation processes and the associated kinetics create this typical pattern remains poorly understood. We monitored tree-ring formation weekly over 3 yr in 45 trees of three conifer species in France. Data were used to model cell development kinetics, and to attribute the relative importance of the duration and rate of cell enlargement and cell wall deposition on tree-ring structure. Cell enlargement duration contributed to 75% of changes in cell diameter along the tree rings. Remarkably, the amount of wall material per cell was quite constant along the rings. Consequently, and in contrast with widespread belief, changes in cell wall thickness were not principally attributed to the duration and rate of wall deposition (33%), but rather to the changes in cell size (67%). Cell enlargement duration, as the main driver of cell size and wall thickness, contributed to 56% of wood density variation along the rings. This mechanistic framework now forms the basis for unraveling how environmental stresses trigger deviations (e. g. false rings) from the normal tree-ring structure

Wood specific gravity (WSG) is a strong predictor of tree performance across environmental gradients. Yet it remains unclear how anatomical elements linked to different wood functions contribute to variation in WSG in branches and roots across tropical forests. We examined WSG and wood anatomy in white sand, clay terra firme and seasonally flooded forests in French Guiana, spanning broad environmental gradients found throughout Amazonia. We measured 15 traits relating to branches and small woody roots in 113 species representing the 15 most abundant species in each habitat and representative species from seven monophyletic lineages occurring in all habitats. Fiber traits appear to be major determinants of WSG, independent of vessel traits, in branches and roots. Fiber traits and branch and root WSG increased from seasonally flooded species to clay terra firme species and lastly to white sand species. Branch and root wood traits were strongly phylogenetically constrained. Lineages differed in wood design, but exhibited similar variation in wood structure across habitats. We conclude that tropical trees can invest differently in support and transport to respond to environmental conditions. Wind disturbance and drought stress represent significant filters driving tree distribution of Amazonian forests; hence we suggest that biophysical explanations should receive more attention.

Leaf out phenology affects a wide variety of ecosystem processes and ecological interactions and will take on added significance as leaf out times increasingly shift in response to warming temperatures associated with climate change. There is, however, relatively little information available on the factors affecting species differences in leaf out phenology. An international team of researchers from eight Northern Hemisphere temperate botanical gardens recorded leaf out dates of c. 1600 woody species in 2011 and 2012. Leaf out dates in woody species differed by as much as 3 months at a single site and exhibited strong phylogenetic and anatomical relationships. On average, angiosperms leafed out earlier than gymnosperms, deciduous species earlier than evergreen species, shrubs earlier than trees, diffuse and semi‐ring porous species earlier than ring porous species, and species with smaller diameter xylem vessels earlier than species with larger diameter vessels. The order of species leaf out was generally consistent between years and among sites. As species distribution and abundance shift due to climate change, interspecific differences in leaf out phenology may affect ecosystem processes such as carbon, water, and nutrient cycling. Our open access leaf out data provide a critical framework for monitoring and modelling such changes going forward.

Background and AimsIn recent years considerable effort has focused on linking wood anatomy and key ecological traits. Studies analysing large databases have described how these ecological traits vary as a function of wood anatomical traits related to conduction and support, but have not considered how these functions interact with cells involved in storage of water and carbohydrates (i.e. parenchyma cells).MethodsWe analyzed, in a phylogenetic context, the functional relationship between cell types performing each of the three xylem functions (conduction, support and storage) and wood density and theoretical conductivity using a sample of approx. 800 tree species from China.Key ResultsAxial parenchyma and rays had distinct evolutionary correlation patterns. An evolutionary link was found between high conduction capacity and larger amounts of axial parenchyma that is probably related to water storage capacity and embolism repair, while larger amounts of ray tissue have evolved with increased mechanical support and reduced hydraulic capacity. In a phylogenetic principal component analysis this association of axial parenchyma with increased conduction capacity and rays with wood density represented orthogonal axes of variation. In multivariate space, however, the proportion of rays might be positively associated with conductance and negatively with wood density, indicating flexibility in these axes in species with wide rays.ConclusionsThe findings suggest that parenchyma types may differ in function. The functional axes represented by different cell types were conserved across lineages, suggesting a significant role in the ecological strategies of the angiosperms.

Abstract The trees of the Cerrado fulfill indispensable roles in climate regulation, hydrological cycle maintenance, and soil preservation, thereby providing essential ecosystem services crucial for environmental equilibrium. Comprehensive knowledge of tree species is imperative for developing effective conservation strategies, aimed at preserving both the biome and its resident species. The objective was to microscopically describe the wood of tree species from a fragment of the Cerrado biome in Minas Gerais. Wood samples were collected from eleven tree species from Cerrado biome. Microscopic examinations were conducted on permanent histological slides and macerated material. This study is particularly significant as it provides new information on the wood of understudied Cerrado species. One of them is Myrsine gardneriana A. DC., a species not previously documented in the literature. The anatomical descriptions of the tree species provided in this work will aid in the identification of species based on their xylem, without the need for vegetative and/or reproductive characteristics. This tool is useful for regulatory bodies overseeing the timber trade and is particularly relevant for the Cerrado biome, especially in monitoring the origin of commercially traded charcoal. Resumo As árvores do Cerrado desempenham papéis indispensáveis na regulação do clima, na manutenção do ciclo hidrológico e na preservação do solo, proporcionando assim, serviços ecossistêmicos essenciais para o equilíbrio ambiental. Um conhecimento abrangente das espécies arbóreas é imperativo para o desenvolvimento de estratégias eficazes de conservação, visando preservar tanto o bioma quanto suas espécies residentes. O objetivo foi descrever microscopicamente a madeira de espécies arbóreas de um fragmento do bioma Cerrado em Minas Gerais. Amostras de madeira foram coletadas de onze espécies arbóreas do bioma Cerrado. Exames microscópicos foram realizados em lâminas histológicas permanentes e em material macerado. Este estudo é particularmente significativo, pois fornece novas informações sobre a madeira de espécies do Cerrado pouco estudadas. Uma delas é Myrsine gardneriana A. DC., uma espécie não documentada anteriormente na literatura. As descrições anatômicas das espécies arbóreas fornecidas neste trabalho auxiliarão na identificação de espécies com base em seu xilema, sem a necessidade de características vegetativas e/ou reprodutivas. Esta ferramenta é útil para órgãos reguladores que supervisionam o comércio de madeira e é particularmente relevante para o bioma Cerrado, especialmente no monitoramento da origem do carvão vegetal comercializado.

Background and Aims: Trees constantly experience wind, perceive resulting mechanical cues, and modify their growth and development accordingly. Previous studies have demonstrated that multiple bending treatments trigger ovalization of the stem and the formation of flexure wood in gymnosperms, but ovalization and flexure wood have rarely been studied in angiosperms, and none of the experiments conducted so far has used multidirectional bending treatments at controlled intensities. Assuming that bending involves tensile and compressive strain, we hypothesized that different local strains may generate specific growth and wood differentiation responses. Methods: Basal parts of young poplar stems were subjected to multiple transient controlled unidirectional bending treatments during 8 weeks, which enabled a distinction to be made between the wood formed under tensile or compressive flexural strains. This set-up enabled a local analysis of poplar stem responses to multiple stem bending treatments at growth, anatomical, biochemical and molecular levels. Key Results: In response to multiple unidirectional bending treatments, poplar stems developed significant cross-sectional ovalization. At the tissue level, some aspects of wood differentiation were similarly modulated in the compressed and stretched zones (vessel frequency and diameter of fibres without a G-layer), whereas other anatomical traits (vessel diameter, G-layer formation, diameter of fibres with a G-layer and microfibril angle) and the expression of fasciclin-encoding genes were differentially modulated in the two zones. Conclusions: This work leads us to propose new terminologies to distinguish the 'flexure wood' produced in response to multiple bidirectional bending treatments from wood produced under transient tensile strain (tensile flexure wood; TFW) or under transient compressive strain (compressive flexure wood; CFW). By highlighting similarities and differences between tension wood and TFW and by demonstrating that plants could have the ability to discriminate positive strains from negative strains, this work provides new insight into the mechanisms of mechanosensitivity in plants.

Cambial injury has been reported to alter wood structure in broad-leaved trees. However, the duration and extension of associated anatomical changes have rarely been analysed thoroughly. A total of 18 young European ash (Fraxinus excelsiorL.) trees injured on the stem by a spring flood were sampled with the aim of comparing earlywood vessels and rays formed prior to and after the scarring event. Anatomical and hydraulic parameters were measured in five successive rings over one-quarter of the stem circumference. The results demonstrate that mechanical damage induces a decrease in vessel lumen size (up to 77%) and an increase in vessel number (up to 475%) and ray number (up to 115%). The presence of more earlywood vessels and rays was observed over at least three years after stem scarring. By contrast, abnormally narrow earlywood vessels mainly developed in the first ring formed after the event, increasing the thickness-to-span ratio of vessels by 94% and reducing both xylem relative conductivity and the index for xylem vulnerability to cavitation by 54% and 32%, respectively. These vessels accumulated in radial groups in a 30° sector immediately adjacent to the wound, raising the vessel grouping index by 28%. The wound-induced anatomical changes in wood structure express the functional need of trees to improve xylem hydraulic safety and mechanical strength at the expense of water transport. Xylem hydraulic efficiency was restored in one year, while xylem mechanical reinforcement and resistance to cavitation and decay lasted over several years.