Seasonal cambial activity of five tropical tree species in central Thailand

The seasonal cambial activity of five tropical tree species was investigated at Khao Yai National Park. The species studied were Tetrameles nudiflora, Magnolia baillonii, Canarium euphyllum Kur, Toona ciliata, and Spondias axillaris. Cambial activity was quantified by counting layers of undifferentiated cells in the cambium zone from wood anatomical micro sections prepared from wood samples collected in monthly intervals from July 2010 to June 2011. The relationship between cambial activity and climatic factors was investigated by using Pearson’s correlation. The growth dynamics of five studied species differed considerably. The cambium of Tetrameles nudiflora and Magnolia baillonii was most active when rainfall reached its maximum amount in June (mid rainy season), whereas the cambium of Canarium euphyllum, Toona ciliata, and Spondias axillaris was most active in March during the transition from the dry to the wet season.     

Fossil wood of <Emphasis Type="Italic">Abietoxylon shakhtnaense</Emphasis> sp. nov. (Pinaceae) from the Upper Oligocene-Lower Miocene deposits of Southeastern Sakhalin

A new species, Abietoxylon shakhtnaense (Pinaceae), was erected on the basis of fossil wood anatomical characters from the Upper Oligocene-Lower Miocene deposits of Southeastern Sakhalin. A. shakhtnaense is similar to wood of firs Abies sachalinensis, A. magnifica, and A. grandis. Fossil wood with features characterizing fir anatomical structure was found in Sakhalin for the first time.     

Improved tree-ring visualization using autofluorescence

The great diversity of wood anatomical features found in trees worldwide results in a broad variety of growth-ring boundary types that are not always easy to recognize, especially in tropical woods. However, the presence of clearly visible limits between tree rings is essential for any tree-ring studies. Here, we propose the use of autofluorescence of wood in order to enhance tree-ring visualization. The multispectral light emitted from the fluorescence stereomicroscope can be filtered in specific wavelengths to improve the visualization of wood anatomical features. To evaluate the effectiveness of this technique, we compared visualization under natural light, GFP (green fluorescent protein) filter, RFP (red fluorescent protein) filter and UV filter. We tested this technique with a set of 38 tree species with different types of growth-ring boundaries. Although results are species-specific, fluorescence has been shown to improve the visualization of growth-ring boundaries by enhancing the contrast among cell types. It may highlight fibrous zones (e.g. Cavanillesia arborea, Aspidosperma polyneuron), different porosity patterns (e.g. Myracrodruon urundeuva), secretory canals (e.g. Copaifera langsdorffii), and parenchyma bands (e.g. Tipuana tipu). Fluorescence allows the visualization of growth-ring boundaries in species that were previously described as having indistinct growth rings under natural light. For species with clear tree-ring boundaries such as Cedrela fissilis and Hymenaea courbaril, this approach aids the identification of false rings. In addition to the visualization of growth-ring boundaries, autofluorescence may be useful for other qualitative and quantitative analyses of wood anatomy, such as wood identification and automated measurements of anatomical features. Scientists struggling with tree-ring counting and cross-dating due to difficult tree-ring visualization may find fluorescence useful. It may also aid to identify new species suitable for tree-ring studies.     

The use of X-ray densitometry to evaluate the wood density profile of Tectona grandis trees growing in fast-growth plantations

Tectona grandis (teak) is an important commercial tree species that is widely used in tropical dendrochronology due to the formation of climate-sensitive annual growth rings. However, young trees growing in plantation conditions exhibit poor ring visibility during the first years of growth, limiting the dendrochronology application. In the present study, we use x-ray densitometry to determine the wood density profile between and within annual rings and at the sapwood-heartwood boundary in trees from fast-growth plantations. The resulting wood density profiles (WDP) can be categorized as uniform, stable growth, unstable growth, and false. The annual ring boundaries were indistinct in trees less than 8 years old. In mature trees, the annual ring boundaries are more defined. In relation to the sapwood-heartwood boundary, the WDP showed a decrease in the wood density; however, this decrease is influenced by the annual ring boundary when the two boundaries coincide. The identification of annual rings in trees growing in fast-growth plantations should be combined with X-ray densitometry and visual identification if wood density data are necessary for deriving other analysis, as climate change, from annual ring.     

Wood density and its radial variation in six canopy tree species differing in shade-tolerance in western Thailand

Background and Aims

Wood density is a key variable for understanding life history strategies in tropical trees. Differences in wood density and its radial variation were related to the shade-tolerance of six canopy tree species in seasonally dry tropical forest in Thailand. In addition, using tree ring measurements, the influence of tree size, age and annual increment on radial density gradients was analysed.

Methods

Wood density was determined from tree cores using X-ray densitometry. X-ray films were digitized and images were measured, resulting in a continuous density profile for each sample. Mixed models were then developed to analyse differences in average wood density and in radial gradients in density among the six tree species, as well as the effects of tree age, size and annual increment on radial increases in Melia azedarach.

Key Results

Average wood density generally reflected differences in shade-tolerance, varying by nearly a factor of two. Radial gradients occurred in all species, ranging from an increase of (approx. 70%) in the shade-intolerant Melia azedarach to a decrease of approx. 13% in the shade-tolerant Neolitsea obtusifolia, but the slopes of radial gradients were generally unrelated to shade-tolerance. For Melia azedarach, radial increases were most-parsimoniously explained by log-transformed tree age and annual increment rather than by tree size.

Conclusions

The results indicate that average wood density generally reflects differences in shade-tolerance in seasonally dry tropical forests; however, inferences based on wood density alone are potentially misleading for species with complex life histories. In addition, the findings suggest that a ‘whole-tree’ view of life history and biomechanics is important for understanding patterns of radial variation in wood density. Finally, accounting for wood density gradients is likely to improve the accuracy of estimates of stem biomass and carbon in tropical trees.Key words: Radial gradients, shade-tolerance, tree biomass estimates, tree rings, tropical trees, wood density     

A new tool for determining degrees of mineralization in fossil amphibian skeletons: The example of the Late Palaeozoic branchiosaurid Apateon from the Autun Basin,France

Studying ontogenetic features of fossil tetrapods is of major interest for investigating the adaptive strategies of early tetrapods to their palaeoenvironments. To determine the degree of calcification of skeletal elements, biologists have until now relied on X-ray radiographs of organisms or isolated bones, or on thin sections. An X-ray tomographic scan of Apateon, a Carboniferous – Permian branchiosaurid from the Autun Basin, France, reveals distinct density properties related to different mineralized tissues (calcified cartilage versus bone). The rendering of Apateon as a “test individual” provides a 3D map of the degrees of ossification of the axial and cranial elements. The combination of these anatomical observations with histological information from classical thin sections made in limb bones of several other specimens of the same locality allows the detailed determination of their ontogenetic stage. A comparison with the well-known specimens of the Saar-Nahe Basin, Germany, makes it possible to investigate the influence of different palaeoenvironments on ontogenetic features.     

Evaluation of X-ray densitometry to identify tree-ring boundaries of two deciduous species from semi-arid forests in Brazil

The presence of visible annual rings in semi-arid tropical trees may allow the application of dendrochronological methods. However, variation in water availability may cause the formation of narrow, irregular ill- or non-defined annual rings hindering the correct dating of tree-ring series. We aimed to evaluate X-ray densitometry as a method to identify tree rings of two deciduous tree species from the Caatinga forest, a semi-arid region in the northeast of Brazil, and compare with two other methods commonly used in dendrochronology, the sliding-stage micrometer and image analysis. Xylem was observed macro- and microscopically and wood anatomical features were assessed in Aspidosperma pyrifolium and Poincianella pyramidalis trees. In both species, tree-ring boundaries were identified considering intra-annual density patterns and wood anatomical features. No significant differences in tree-ring widths were found among methods. X-ray densitometry measurements showed a positive correlation with the measurements obtained with image analysis and sliding-stage micrometer in A. pyrifolium and P. pyramidalis, revealing the high reliability of the methods used. However, inter-correlation of tree-ring width series showed differences in the accuracy of crossdating across measuring methods. The maximum, mean and minimum density values were species-dependent, with mean wood density of A. pyrifolium lower than P. pyramidalis. Our results highlight X-ray densitometry as an important and complementary tool to identify tree-rings boundaries in semi-arid tree species, especially in A. pyrifolium. Along with other measuring methods, it may provide higher accuracy in dendrochronological studies in semi-arid or subtropical environments.     

Testing species delimitation in sympatric species complexes: the case of an African tropical tree, Carapa spp. (Meliaceae)

Plant species delimitation within tropical ecosystems is often difficult because of the lack of diagnostic morphological characters that are clearly visible. The development of an integrated approach, which utilizes several different types of markers (both morphological and molecular), would be extremely useful in this context. Here we have addressed species delimitation of sympatric tropical tree species that belong to Carapa spp. (Meliaceae) in Central Africa. We adopted a population genetics approach, sampling numerous individuals from three locations where sympatric Carapa species are known to exist. Comparisons between morphological markers (the presence or absence of characters, leaf-shape traits) and molecular markers (chloroplast sequences, ribosomal internal transcribed spacer region (ITS) sequences, and nuclear microsatellites) demonstrated the following: (i) a strong correlation between morphological and nuclear markers; (ii) despite substantial polymorphism, the inability of chloroplast DNA to discriminate between species, suggesting that cytoplasmic markers represent ineffective DNA barcodes; (iii) lineage sorting effects when using ITS sequences; and (iv) a complex evolutionary history within the genus Carapa, which includes frequent inter-specific gene flow. Our results support the use of a population genetics approach, based on ultra-polymorphic markers, to address species delimitation within complex taxonomic groups.     

Development of Genetic Markers in Eucalyptus Species by Target Enrichment and Exome Sequencing

The advent of next-generation sequencing has facilitated large-scale discovery, validation and assessment of genetic markers for high density genotyping. The present study was undertaken to identify markers in genes supposedly related to wood property traits in three Eucalyptus species. Ninety four genes involved in xylogenesis were selected for hybridization probe based nuclear genomic DNA target enrichment and exome sequencing. Genomic DNA was isolated from the leaf tissues and used for on-array probe hybridization followed by Illumina sequencing. The raw sequence reads were trimmed and high-quality reads were mapped to the E. grandis reference sequence and the presence of single nucleotide variants (SNVs) and insertions/ deletions (InDels) were identified across the three species. The average read coverage was 216X and a total of 2294 SNVs and 479 InDels were discovered in E. camaldulensis, 2383 SNVs and 518 InDels in E. tereticornis, and 1228 SNVs and 409 InDels in E. grandis. Additionally, SNV calling and InDel detection were conducted in pair-wise comparisons of E. tereticornis vs. E. grandis, E. camaldulensis vs. E. tereticornis and E. camaldulensis vs. E. grandis. This study presents an efficient and high throughput method on development of genetic markers for family– based QTL and association analysis in Eucalyptus.     

Wood Specific Gravity Variations and Biomass of Central African Tree Species: The Simple Choice of the Outer Wood

Context

Wood specific gravity is a key element in tropical forest ecology. It integrates many aspects of tree mechanical properties and functioning and is an important predictor of tree biomass. Wood specific gravity varies widely among and within species and also within individual trees. Notably, contrasted patterns of radial variation of wood specific gravity have been demonstrated and related to regeneration guilds (light demanding vs. shade-bearing). However, although being repeatedly invoked as a potential source of error when estimating the biomass of trees, both intraspecific and radial variations remain little studied. In this study we characterized detailed pith-to-bark wood specific gravity profiles among contrasted species prominently contributing to the biomass of the forest, i.e., the dominant species, and we quantified the consequences of such variations on the biomass.

Methods

Radial profiles of wood density at 8% moisture content were compiled for 14 dominant species in the Democratic Republic of Congo, adapting a unique 3D X-ray scanning technique at very high spatial resolution on core samples. Mean wood density estimates were validated by water displacement measurements. Wood density profiles were converted to wood specific gravity and linear mixed models were used to decompose the radial variance. Potential errors in biomass estimation were assessed by comparing the biomass estimated from the wood specific gravity measured from pith-to-bark profiles, from global repositories, and from partial information (outer wood or inner wood).

Results

Wood specific gravity profiles from pith-to-bark presented positive, neutral and negative trends. Positive trends mainly characterized light-demanding species, increasing up to 1.8 g.cm^-3 per meter for Piptadeniastrum africanum, and negative trends characterized shade-bearing species, decreasing up to 1 g.cm^-3 per meter for Strombosia pustulata. The linear mixed model showed the greater part of wood specific gravity variance was explained by species only (45%) followed by a redundant part between species and regeneration guilds (36%). Despite substantial variation in wood specific gravity profiles among species and regeneration guilds, we found that values from the outer wood were strongly correlated to values from the whole profile, without any significant bias. In addition, we found that wood specific gravity from the DRYAD global repository may strongly differ depending on the species (up to 40% for Dialium pachyphyllum).

Main Conclusion

Therefore, when estimating forest biomass in specific sites, we recommend the systematic collection of outer wood samples on dominant species. This should prevent the main errors in biomass estimations resulting from wood specific gravity and allow for the collection of new information to explore the intraspecific variation of mechanical properties of trees.     

Stem anatomy of Rhipsalis (Cactaceae) and its relevance for taxonomy

Several species of the genus Rhipsalis (Cactaceae) are extremely important as ornamentals and are endangered in their natural habitat. However, only a few studies have addressed its taxonomy, morphology (including anatomy), phylogeny and evolutionary history. Consequently, the limited knowledge of the genus coupled with the problematic delimitation of species had led to problems in the identification of taxa. In the current work six species of Rhipsalis, R. cereoides, R. elliptica, R. grandiflora, R. paradoxa, R. pentaptera and R. teres were studied to evaluate the relevance of anatomical characters for the taxonomy of the genus. An anatomical characterization of the primary structure of the stem of Rhipsalis is provided highlighting the differences between species. Features of the stem epidermis are found to discriminate best between species and therefore provide clear and useful characters for the separation of species.     

Targeted re-sequencing and genome-wide association analysis for wood property traits in breeding population of Eucalyptus tereticornis × E. grandis

Globally, Eucalyptus plantations occupy 22 million ha area and is one of the preferred hardwood species due to their short rotation, rapid growth, adaptability and wood properties. In this study, we present results of GWAS in parents and 100 hybrids of Eucalyptus tereticornis × E. grandis using 762 genes presumably involved in wood formation. Comparative analysis between parents predicted 32,202 polymorphic SNPs with high average read depth of 269-562× per individual per nucleotide. Seventeen wood related traits were phenotyped across three diverse environments and GWAS was conducted using 13,610 SNPs. A total of 45 SNP-trait associations were predicted across two locations. Seven large effect markers were identified which explained more than 80% of phenotypic variation for fibre area. This study has provided an array of candidate genes which may govern fibre morphology in this genus and has predicted potential SNPs which can guide future breeding programs in tropical Eucalyptus.     

Cryptic species in tropic sands--interactive 3D anatomy, molecular phylogeny and evolution of meiofaunal Pseudunelidae (Gastropoda, Acochlidia)

Background

Towards realistic estimations of the diversity of marine animals, tiny meiofaunal species usually are underrepresented. Since the biological species concept is hardly applicable on exotic and elusive animals, it is even more important to apply a morphospecies concept on the best level of information possible, using accurate and efficient methodology such as 3D modelling from histological sections. Molecular approaches such as sequence analyses may reveal further, cryptic species. This is the first case study on meiofaunal gastropods to test diversity estimations from traditional taxonomy against results from modern microanatomical methodology and molecular systematics.

Results

The examined meiofaunal Pseudunela specimens from several Indo-Pacific islands cannot be distinguished by external features. Their 3D microanatomy shows differences in the organ systems and allows for taxonomic separation in some cases. Additional molecular analyses based on partial mitochondrial cytochrome c oxidase subunit I (COI) and 16S rRNA markers revealed considerable genetic structure that is largely congruent with anatomical or geographical patterns. Two new species (Pseudunela viatoris and P. marteli spp. nov.) are formally described integrating morphological and genetic analyses. Phylogenetic analysis using partial 16S rRNA, COI and the nuclear 18S rRNA markers shows a clade of Pseudunelidae species as the sister group to limnic Acochlidiidae. Within Pseudunela, two subtypes of complex excretory systems occur. A complex kidney already evolved in the ancestor of Hedylopsacea. Several habitat shifts occurred during hedylopsacean evolution.

Conclusions

Cryptic species occur in tropical meiofaunal Pseudunela gastropods, and likely in other meiofaunal groups with poor dispersal abilities, boosting current diversity estimations. Only a combined 3D microanatomical and molecular approach revealed actual species diversity within Pseudunela reliably. Such integrative methods are recommended for all taxonomic approaches and biodiversity surveys on soft-bodied and small-sized invertebrates. With increasing taxon sampling and details studied, the evolution of acochlidian panpulmonates is even more complex than expected.     

Revisiting the stem proteome of Eucalyptus grandis and Eucalyptus globulus: Identification of temperature-induced changes

Eucalyptus grandis and Eucalyptus globulus are important species for the Brazilian forestry industry. E. grandis plantations are mainly found in tropical regions, yet E. globulus plants are usually cultivated under moderate to low temperature conditions. As temperature seems to be a key factor for the planting of these species, we revisited our previously generated shotgun proteomics dataset to identify the main patterns of proteome regulation induced by thermal stimulus and to pinpoint specific proteins involved in the environmental response. Large-scale analysis has pointed out the different proteomic responses of E. grandis and E. globulus under temperature stimulus, with 296 proteins considered to be differentially regulated in the stems of Eucalyptus spp. grown at different temperatures. A stringent filtering approach was used to identify the most differentially regulated proteins. Through the stringent criteria, 66 proteins were found to be enriched in the plant species. Cultivation of E. globulus plants in low-temperature conditions induced the highest number of differentially regulated proteins. Additionally, metabolic proteins were mostly down-regulated, while stress-related proteins were majorly up-regulated in both species. Finally, the subset of the most differentially regulated proteins comprised new candidates of protein markers of temperature stress.     

Exploring wood anatomy,density and chemistry profiles to understand the tree-ring formation in Amazonian tree species

Long-term analysis of tree growth using annual tree rings is increasingly in demand for tropical tree species. The basis of these studies has traditionally been the anatomical identification of the annual ring boundary. However, the structure of these annual rings has been sparsely explored for complementary physical and chemical wood traits. Here, we explore the relationships among wood density features and chemical elements (S, K, Ca, Mn) involved in the annual tree ring formation of 12 tropical tree species from non-flooded forest in the southern Amazon basin. Transverse wood sections were used for each species to determine: 1) macroscopic distinction (radial growth and wood density), 2) microscopic analyse of vessels, axial and ray parenchyma (anatomy) and 3) X-ray densitometry (physical) and X-ray fluorescence (chemical). For some species, the profiles of wood density, and Ca and Mn content showed intra- and inter-annual patterns that allowed to define and characterize the growth boundary of tree rings. Ca, K and S were mainly distributed in axial parenchyma cells, and around vessels, whereas, Mn was mainly distributed in fibres. Our results showed significant species-specific correlations between tree-ring width, density and concentrations of Ca, K and Mn. The anatomical characterization and the complementary information provided by the density and chemical profiles in some Amazonian species can represent a valuable proxy to improve the definition of annual ring-boundaries and improve the understanding of long-term growth and physiological patterns.     

Wood anatomy and vessel characteristics of spiny monkey orange (Strychnos spinosa) in Benin (West Africa)

The response of plant species to varying climate conditions in tropical Africa remains poorly understood but can be assessed using wood anatomical traits. These traits play an important role for the adaptive capacity of a species to environmental stress, since environmental conditions can modify the proportion, size, and morphology of wood anatomical elements. This study reports quantitative data on vessel characteristics of the diffuse porous angiosperm Spiny monkey orange (Strychnos spinosa Lam.) in Benin in tropical West Africa. The vessel-related anatomical traits varied with high amplitude (coefficient of variation CV ˃ 25%) between different sites located in different climate zones. The variability of the traits is higher within one climatic zone than between climatic zones, and even more pronounced within trees. Consequently, the climatic zones have less influence on the studied features than local site conditions. However, the study showed that S. spinosa individuals that have numerous vessels also have a high lumen fraction and total ring area. On the other hand, individuals presenting a high vessel density also display vessels of smaller size. The correlation between vessel number and total ring area on the one hand, and between vessel size and lumen fraction on the other hand are highly significant and positive. In Benin, S. spinosa wood anatomical traits are likely linked to local site factors rather than to regional climatic factors.     

Fossil wood of Keteleerioxylon kamtschatkiense sp. nov. (Pinaceae) from the Cretaceous of the northwestern Kamchatka Peninsula

A new species, Keteleerioxylon kamtschatkiense, is described from the Cretaceous of the northwestern Kamchatka Peninsula on the basis of wood anatomy. Fossil wood showing anatomical characters of the modern genus Keteleeria is described from the Cretaceous of the Russian Far East for the first time.