Physiological, Biochemical, and Molecular Analyses Reveal Dark Heartwood Formation Mechanism in Acacia melanoxylon.

Acacia melanoxylon is highly valued for its commercial applications, with the heartwood exhibiting a range of colors from dark to light among its various clones. The underlying mechanisms contributing to this color variation, however, have not been fully elucidated. In an effort to understand the factors that influence the development of dark heartwood, a comparative analysis was conducted on the microstructure, substance composition, differential gene expression, and metabolite profiles in the sapwood (SW), transition zone (TZ), and heartwood (HW) of two distinct clones, SR14 and SR25. A microscopic examination revealed that heartwood color variations are associated with an increased substance content within the ray parenchyma cells. A substance analysis indicated that the levels of starches, sugars, and lignin were more abundant in SP compared to HW, while the concentrations of phenols, flavonoids, and terpenoids were found to be higher in HW than in SP. Notably, the dark heartwood of the SR25 clone exhibited greater quantities of phenols and flavonoids compared to the SR14 clone, suggesting that these compounds are pivotal to the color distinction of the heartwood. An integrated analysis of transcriptome and metabolomics data uncovered a significant accumulation of sinapyl alcohol, sinapoyl aldehyde, hesperetin, 2', 3, 4, 4', 6'-peptahydroxychalcone 4'-O-glucoside, homoeriodictyol, and (2S)-liquiritigenin in the heartwood of SR25, which correlates with the up-regulated expression of CCRs (evm.TU.Chr3.1751, evm.TU.Chr4.654_667, evm.TU.Chr4.675, evm.TU.Chr4.699, and evm.TU.Chr4.704), COMTs (evm.TU.Chr13.3082, evm.TU.Chr13.3086, and evm.TU.Chr7.1411), CADs (evm.TU.Chr10.2175, evm.TU.Chr1.3453, and evm.TU.Chr8.1600), and HCTs (evm.TU.Chr4.1122, evm.TU.Chr4.1123, evm.TU.Chr8.1758, and evm.TU.Chr9.2960) in the TZ of A. melanoxylon. Furthermore, a marked differential expression of transcription factors (TFs), including MYBs, AP2/ERFs, bHLHs, bZIPs, C2H2s, and WRKYs, were observed to be closely linked to the phenols and flavonoids metabolites, highlighting the potential role of multiple TFs in regulating the biosynthesis of these metabolites and, consequently, influencing the color variation in the heartwood. This study facilitates molecular breeding for the accumulation of metabolites influencing the heartwood color in A. melanoxylon, and offers new insights into the molecular mechanisms underlying heartwood formation in woody plants.

Letter to the editor on "in vitro & in silico study of hypoglycaemic potential of pterocarpus marsupium heartwood extract".

The Short Communication "In vitro & in silico study of hypoglycemic potential of Pterocarpus marsupium heartwood extract" published in Natural Product Research is praised for its depth of inquiry and exploration of hypoglycemic and antioxidant properties. However, there are areas for refinement, such as clearer definitions of key terms related to type 2 diabetes mellitus, updated literature review, improved organization and contextualization of the Results and Discussion section, and a more balanced discussion of the study's implications.

Stem moisture content prediction model for Larix olgensis based on beta regression.

To investigate the longitudinal variation patterns of sapwood, heartwood, bark and stem moisture content along the trunk of artificial Larix olgensis, we constructed mixed effect models of moisture content based on beta regression by combining the effects of sampling plot and sample trees. We used two sampling schemes to calibrate the model, without limiting the relative height (Scheme Ⅰ) and with a limiting height of less than 2 m (Scheme II). The results showed that sapwood and stem moisture content increased gradually along the trunk, heartwood moisture content decreased slightly and then increased along the trunk, and bark moisture content increased along the trunk and then levelled off before increasing. Relative height, height to crown base, stand area at breast height per hectare, age, and stand dominant height were main factors driving moisture content of L. olgensis. Scheme Ⅰ showed the stable prediction accuracy when randomly sampling moisture content measurements from 2-3 discs to calibrate the model, with the mean absolute percentage error (MAPE) of up to 7.2% for stem moisture content (randomly selected 2 discs), and the MAPE of up to 7.4%, 10.5% and 10.5% for sapwood, heartwood and bark moisture content (randomly selected 3 discs), respectively. Scheme Ⅱ was appropriate when sampling moisture content measurements from discs of 1.3 and 2 m height and the MAPE of sapwood, heartwood, bark and stem moisture content reached 7.8%, 11.0%, 10.4% and 7.1%, respectively. The prediction accuracies of all mixed effect beta regression models were better than the base model. The two-level mixed effect beta regression models, considering both plot effect and tree effect, would be suitable for predicting moisture content of each part of L. olgensis well.

Comparative physiological, biochemical, metabolomic, and transcriptomic analyses reveal the formation mechanism of heartwood for Acacia melanoxylon.

Acacia melanoxylon is well known as a valuable commercial tree species owing to its high-quality heartwood (HW) products. However, the metabolism and regulatory mechanism of heartwood during wood development remain largely unclear. In this study, both microscopic observation and content determination proved that total amount of starches decreased and phenolics and flavonoids increased gradually from sapwood (SW) to HW. We also obtained the metabolite profiles of 10 metabolites related to phenolics and flavonoids during HW formation by metabolomics. Additionally, we collected a comprehensive overview of genes associated with the biosynthesis of sugars, terpenoids, phenolics, and flavonoids using RNA-seq. A total of ninety-one genes related to HW formation were identified. The transcripts related to plant hormones, programmed cell death (PCD), and dehydration were increased in transition zone (TZ) than in SW. The results of RT-PCR showed that the relative expression level of genes and transcription factors was also high in the TZ, regardless of the horizontal or vertical direction of the trunk. Therefore, the HW formation took place in the TZ for A. melanoxylon from molecular level, and potentially connected to plant hormones, PCD, and cell dehydration. Besides, the increased expression of sugar and terpenoid biosynthesis-related genes in TZ further confirmed the close connection between terpenoid biosynthesis and carbohydrate metabolites of A. melanoxylon. Furthermore, the integrated analysis of metabolism data and RNA-seq data showed the key transcription factors (TFs) regulating flavonoids and phenolics accumulation in HW, including negative correlation TFs (WRKY, MYB) and positive correlation TFs (AP2, bZIP, CBF, PB1, and TCP). And, the genes and metabolites from phenylpropanoid and flavonoid metabolism and biosynthesis were up-regulated and largely accumulated in TZ and HW, respectively. The findings of this research provide a basis for comprehending the buildup of metabolites and the molecular regulatory processes of HW formation in A. melanoxylon.

Water, starch, and nuclear behavior in ray parenchyma during heartwood formation of Catalpa bungei 'Jinsi'.

Catalpa bungei 'Jinsi', a cultivar of C. bungei C. A. Mey., is valued for its heartwood with good overall mechanical properties, naturally durable and golden-yellow color. Little is known about heartwood formation in C. bungei 'Jinsi' trees. The behavior of starch, water, and nuclei was studied in the xylem tissue of C. bungei 'Jinsi' concerning aging in ray parenchyma cells. Blocks containing heartwood, golden zone, transition zone, and sapwood were collected from the stems of six C. bungei 'Jinsi' trees. The moisture content of the blocks was measured by oven drying. Changes in starch and nuclei in ray parenchyma were investigated in radial profiles from sapwood to heartwood blocks using microscopy and various staining techniques. The nuclear size and starch content gradually decreased to heartwood. While the horizontal distribution of moisture content of C. bungei 'Jinsi' was very varied, with the heartwood and golden zone being lower than sapwood but slightly higher than the transition zone. Starch grains were rare, but nuclei were still present in some ray parenchyma cells in the heartwood and golden zone. The nuclei showed irregular shape and elongation before disintegration. These results suggest that the most apparent change occurs in the transition zone, the critical location involved in forming C. bungei 'Jinsi' heartwood. Water and starch appear to be actively engaged in heartwood formation. The loss of function of ray parenchyma cells results from heartwood formation.

Retrieving complete plastid genomes of endangered Guibourtia timber using hybridization capture for forensic identification and phylogenetic analysis.

The high economic value and increased demand for timber have led to illegal logging and overexploitation, threatening wild populations. In this context, there is an urgent need to develop effective and accurate forensic tools for identifying endangered Guibourtia timber species to protect forest ecosystem resources and regulate their trade. In this study, a hybridization capture method was developed and applied to explore the feasibility of retrieving complete plastid genomes from Guibourtia sapwood and heartwood specimens stored in a xylarium (wood collection). We then carried out forensic identification and phylogenetic analyses of Guibourtia within the subfamily Detarioideae. This study is the first to successfully retrieve high-quality plastid genomes from xylarium specimens, with 76.95-99.97% coverage. The enrichment efficiency, sequence depth, and coverage of plastid genomes from sapwood were 16.73 times, 70.47 times and 1.14 times higher, respectively, than those from heartwood. Although the DNA capture efficiency of heartwood was lower than that of sapwood, the hybridization capture method used in this study is still suitable for heartwood DNA analysis. Based on the complete plastid genome, we identified six endangered or commonly traded Guibourtia woods at the species level. This technique also has the potential for geographical traceability, especially for Guibourtia demeusei and Guibourtia ehie. Meanwhile, Bayesian phylogenetic analysis suggested that these six Guibourtia species diverged from closely related species within the subfamily Detarioideae ca. 18 Ma during the Miocene. The DNA reference database established based on the xylarium specimens provides admissible evidence for diversity conservation and evolutionary analyses of endangered Guibourtia species.

Methane and nitrous oxide emissions and related microbial communities from mangrove stems on Qi'ao Island, Pearl River Estuary in China.

Mangrove forests, crucial carbon-rich ecosystems, are increasingly vulnerable to soil carbon loss and greenhouse gas (GHG) emissions due to human disturbance. However, the contribution of mangrove trees to GHG emissions remains poorly understood. This study monitored CO2, CH4, and N2O fluxes from the stems of two mangrove species, native Kandelia obovata (KO) and exotic Sonneratia apetala (SA), at three heights (0.7 m, 1.2 m, and 1.7 m) during the dry winter period on Qi'ao Island, Pearl River Estuary, China. Heartwood samples were analyzed to identify potential functional groups related to gas fluxes. Our study found that tree stems acted as both sinks and sources for N2O (ranging from -9.49 to 28.35 µg m-2 h-1 for KO and from -6.73 to 28.95 µg m-2 h-1 for SA) and CH4. SA exhibited significantly higher stem CH4 flux (from -26.67 to 97.33 µg m-2 h-1) compared to KO (from -44.13 to 88.0 µg m-2 h-1) (P < 0.05). When upscaled to the community level, both species were net emitters of CH4, contributing approximately 4.68 % (KO) and 0.51 % (SA) to total CH4 emissions. The decrease in stem CH4 flux with increasing height, indicates a soil source. Microbial analysis in the heartwood using the KEGG database indicated aceticlastic methanogenesis as the dominant CH4 pathway. The presence of methanogens, methanotrophs, denitrifiers, and nitrifiers suggests microbial involvement in CH4 and N2O production and consumption. Remarkably, the dominance of Cyanobacteria in the heartwood microbiome (with the relative abundance of 97.5 ± 0.6 % for KO and 99.1 ± 0.2 % for SA) implies roles in carbon and nitrogen fixation for mangroves coping with nitrogen limitation in coastal wetlands, and possibly in CH4 production. Although the present study has limitations in sampling duration and area, it highlights the significant role of tree stems in GHG emissions which is crucial for a holistic evaluation of the global carbon sequestration capability of mangrove ecosystems. Future research should broaden spatial and temporal scales to enhance the accuracy of upscaling tree stem gas fluxes to the mangrove ecosystem level.

Cambial Age Influences PCD Gene Expression during Xylem Development and Heartwood Formation.

Heartwood formation is an important ontogenetic stage in Scots pine (Pinus sylvestris L.). The amount of heartwood determines the proportion of functionally active sapwood in the total trunk biomass as well as the quality of wood. The key criterion for heartwood formation is the death of xylem ray parenchyma cells. Previously, models that described the patterns of heartwood formation, depending on the cambial age, were derived from Scots pine trees of different ages. The cambial age is the number of annual xylem layers at the core sampling site at a certain trunk height. We studied the features of the occurrence of programmed cell death (PCD) processes during the xylem differentiation and heartwood formation of 80-year-old Scots pine trees, depending on the cambial age, under the lingonberry pine forest conditions in the transition area of the northern taiga subzone and tundra. We have shown that the distance from the cambial zone to the heartwood boundary does not change significantly with stem height. As the cambial age increases, the lifespan of the formed xylem ray parenchyma cells increases and the activity of PCD genes decreases during the formation of both (1) xylem (in the outer layers of sapwood) and (2) heartwood (in the inner layers of sapwood and transition zone). We hypothesized that the decisive factor in the PCD initiation during heartwood formation is the distance of the xylem ray parenchyma cells from the cambial zone. The younger cambium forms wider annual increments, and therefore the xylem ray parenchyma cells in these parts of the trunk reach the distance from the cambial zone earlier, which is necessary for PCD initiation.

Transcriptomic monitoring of Douglas-fir heartwood formation.

OBJECTIVES: Molecular cues linked to heartwood formation open new (complementary) perspectives to genetic breeding programs of Douglas-fir, a tree species largely cultivated in Europe for the natural durability and civil engineering properties of its wood. DATA DESCRIPTION: RNAs from a single genotype of Douglas-fir, extracted from three distinct wood zones (outer sapwood, inner sapwood and transition zone) at four vegetative seasons to generate an extensive RNA-seq dataset used to apprehend the in-wood dynamic and seasonality of heartwood formation in this hardwood model species. Previously published data collected on somatic embryos of the same genotype could be merged with the present dataset to upgrade grade the Douglas-fir reference transcriptome.

Changes in the physiological activity of parenchyma cells in Dalbergia odorifera xylem and its relationship with heartwood formation.

BACKGROUND: The formation of a tree's heartwood gives the wood properties such as natural decay resistance and aesthetic color, and often directly determines the value of wood products. Regulating the quantity and quality of heartwood is of great importance to the use of wood. However, the mechanism of heartwood formation has been poorly understood. RESULTS: Using Dalbergia odorifera as the study species, the number of starch grains, the morphology of the nuclei, the changes in the content of water and secondary metabolites were observed continuously in the radial direction of the xylem. The results show that from the outer toward inner sapwood, the starch grains are abundant, the length to diameter ratio of the nuclei is decreasing, and the morphology changes from elongated elliptical and then to round. In the outer transition zone, the starch grains begin to decrease abruptly and the nuclei shrink at a slower rate, with a radial width of approximately 2 mm. In the inner transition zone, the heartwood color begins to appear, the starch grains disappear and a few nuclei with reduced fluorescence are present, with a radial width of approximately 1 mm. Heartwood formation after complete disappearance of the nuclei. The moisture content of the heartwood is higher than that of the sapwood, and the inner transition zone is where the content rises. The secondary metabolites of the heartwood begin to accumulate in large quantities in the inner transition zone. CONCLUSION: Based on the physiological changes of parenchyma cells in the xylem, the radial width of the transition zone of Dalbergia odorifera is clearly defined as approximately 3 mm. Both the water and secondary metabolite abrupt changes occur at the final stage of programmed cell death, and neither is a direct cause of programmed cell death in parenchyma cells.

Phytochemical Analysis of Pinus cembra Heartwood-UHPLC-DAD-ESI-MSn with Focus on Flavonoids, Stilbenes, Bibenzyls and Improved HPLC Separation.

The heartwood of the Swiss Stone Pine, Pinus cembra L., has been scarcely investigated for secondary metabolites for a long period of time. Considering age and relative simplicity of heartwood investigations dating back to the 1940s to 1960s, we conducted the first investigation of P. cembra heartwood by HPLC, using UHPLC-DAD-ESI-MSn and HPLC-DAD techniques in combination with isolation and NMR spectroscopy, with focus on stilbenes, bibenzyls and flavonoids. Analytical problems in the HPLC analysis of Pinus stilbenes and flavonoids on reversed stationary phases were also challenged, by comparing HPLC on pentafluorophenyl (PFP) and C18 stationary phases. Seven flavonoids (1, 2, 3, 7, 8, 11, 12), four stilbenes (4, 6, 10, 13), two bibenzyls (5, 9), three fatty acids (14, 16, 17) and one diterpenic acid (15) were detected in an ethanolic extract of Pinus cembra heartwood. HPLC comparison of reversed stationary phases in HPLC showed that the antifungal, antibacterial and chemosensitizing dihydropinosylvin monomethyl ether (9) and pinosylvin monomethyl ether (10) can be separated on PFP, but not on C18 material, when eluting with a screening gradient of 20-100% acetonitrile. Flavonoid separation showed additional benefits of combining analyses on different stationary phases, as flavonoids 7 and 8 could only be separated on one of two C18 stationary phases. Earlier phytochemical results for heartwood investigations were shown to be mostly correct, yet expandable. Substances 5 to 12 were found in alignment with these references, proving remarkable phytochemical analyses at the time. Evidence for the described presence of pinobanksin could not be found. Substances 1 to 4 and 13 have to our knowledge not yet been described for P. cembra.

Exploring the Potential of Roselle Calyx and Sappan Heartwood Extracts as Natural Colorants in Poly(butylene Succinate) for Biodegradable Packaging Films.

Recently, there has been a growing concern among consumers regarding the safety of packaging products, particularly due to the presence of potentially harmful substances like synthetic pigments and inorganic dyes. These substances, which are often used to attract consumer attention, can migrate and contaminate products over extended shelf storage periods. To address this issue, the focus of this research was the development of a biodegradable packaging film using poly(butylene succinate) (PBS) incorporated with natural colorants extracted from roselle (RS) and sappan heartwood (SP). RS and SP serve as non-toxic and alternative pigments when compared to synthetic colorants. The biodegradable packaging films were prepared using blown film extrusion, encompassing different weight percentages of RS and SP (0.1%, 0.2%, and 0.3%). The films exhibited distinct colors, with RS films appearing pink to purple and SP films exhibiting an orange hue. The water vapor transmission rate slightly decreased with an increasing content of RS and SP extracts, indicating improved barrier properties. Additionally, the films showed reduced light transmittance, as evidenced by the UV-Vis light barrier results. The degree of crystallinity in the films was enhanced, as confirmed by X-ray diffraction and differential scanning calorimetry techniques. Regarding mechanical properties, the PBS/RS and PBS/SP films exhibited slight increases in tensile strength and elongation compared to neat PBS films. Moreover, the blended films demonstrated higher stability after undergoing an aging test, further highlighting their potential for use in biodegradable packaging applications. The key advantages of these films lie in their non-toxicity, biodegradability, and overall environmental friendliness.

Comparative Metabolomics and Transcriptome Analysis Reveal the Fragrance-Related Metabolite Formation in Phoebe zhennan Wood.

Nanmu (Phoebe zhennan) has a unique fragrance and is a high-quality tree species for forest conservation. The types and contents of volatile compounds in different tissues of nanmu wood are different, and the study of its volatile metabolites can help us to understand the source of its fragrance and functions. In order to explore the metabolites related to the wood fragrance of nanmu and to find out the unique volatile substances in the heartwood, gas chromatography-mass spectrometry (GC-MS) was performed to analyze the non-targeted metabolomics in five radial tissues from the sapwood to the heartwood of nanmu. A total of 53 volatile metabolites belonging to 11 classes were detected in all tissues, including terpenes, aromatic hydrocarbons, organoheterocyclics, phenols, esters, organic acids, alcohols, alkaloids, alkane, indoles derivatives, and others. And most of the volatile metabolites were identified for the first time in nanmu wood. Among them, terpenes and aromatic hydrocarbons were the main volatile components. In addition, 22 differential metabolites were screened from HW and SW, HW, and TZ via metabolomic analysis. Among these DAMs, three volatile metabolites (cadinene, a sesquiterpenoid; p-cymene, a monoterpenoid; 1,3,5-triisopropylbenzene, an aromatic hydrocarbon) contributed heavily to the characteristic fragrance of the heartwood. Additionally, the expression of transcripts showed that the unigenes in the terpenoid biosynthesis pathway were especially up-regulated in the SW. Therefore, we speculated that fragrance-related metabolites were synthesized in SW and then deposited in heartwood during sapwood transformed to heartwood. The expression levels of transcription factors (e.g., WRKY, C2H2, NAC) acted as the major regulatory factors in the synthesis of terpenoid. The results lay the foundations for further studies on the formation mechanism of fragrance components in nanmu wood and also provide a reference for the further development and utilization of nanmu wood.

A Comprehensive Review on Bioactive Compounds Found in Caesalpinia sappan.

Sappan wood (Caesalpinia sappan) is a tropical hardwood tree found in Southeast Asia. Sappan wood contains a water-soluble compound, which imparts a red color named brazilin. Sappan wood is utilized to produce dye for fabric and coloring agents for food and beverages, such as wine and meat. As a valuable medicinal plant, the tree is also known for its antioxidant, anti-inflammatory, and anticancer properties. It has been observed that sappan wood contains various bioactive compounds, including brazilin, brazilein, sappan chalcone, and protosappanin A. It has also been discovered that these substances have various health advantages; they lower inflammation, enhance blood circulation, and are anti-oxidative in nature. Sappan wood has been used as a medicine to address a range of illnesses, such as gastrointestinal problems, respiratory infections, and skin conditions. Studies have also suggested that sappan wood may have anticarcinogenic potential as it possesses cytotoxic activity against cancer cells. Based on this, the present review emphasized the different medicinal properties, the role of phytochemicals, their health benefits, and several food and nonfood applications of sappan wood. Overall, sappan wood has demonstrated promising medicinal properties and is an important resource in traditional medicine. The present review has explored the potential role of sappan wood as an essential source of bioactive compounds for drug development.

Savinin Triggers Programmed Cell Death of Ray Parenchyma Cells in Heartwood Formation of Taiwania cryptomerioides Hayata.

The purpose of this study was to investigate the relationship between lignan biosynthesis and programmed cell death (PCD) of ray parenchyma cells during the heartwood formation of Taiwania (Taiwania cryptomerioides Hayata). Since the PCD of ray parenchyma cells and the synthesis of lignans are the two main processes involved in the formation of heartwood, both of which need to be completed through gene regulation. Based on the results of genomics and bioinformatics analysis, that the PCD of tracheids are induced by genotoxic, and the PCD of ray parenchyma cells is induced by biological factors, such as fungi, bacteria, and viruses, which could induce oxidative stress. According to the results of time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis, lignans are produced in ray parenchyma cells, and the accumulation of savinin and its downstream lignans might be the cause of PCD in ray parenchyma cells. An in vitro experiment further confirmed that the accumulation of savinin could cause protoplasts of Taiwania's xylem to produce taiwanin A, which is the marker of heartwood formation in Taiwania. Resulting in an increase in reactive oxygen species (ROS) content, which could induce oxidative stress in ray parenchyma cells and potentially lead to PCD. Based on these findings, we conclude that accumulation of savinin could be induced PCD of ray parenchyma cells in heartwood formation in Taiwania.

Function of the R2R3-MYB Transcription Factors in Dalbergia odorifera and Their Relationship with Heartwood Formation.

R2R3-MYB transcription factors (TFs) form one of the most important TF families involved in regulating various physiological functions in plants. The heartwood of Dalbergia odorifera is a kind of high-grade mahogany and valuable herbal medicine with wide application. However, the role of R2R3-MYB genes in the growth and development of D. odorifera, especially their relevance to heartwood formation, has not been revealed. A total of 126 R2R3-MYBs were screened from the D. odorifera genome and named DodMYB1-126 based on their location on 10 chromosomes. The collinearity results showed that purification selection was the main driving force for the evolution of the R2R3-MYB TFs family, and whole genome/fragment replication event was the main form for expanding the R2R3-MYB family, generating a divergence of gene structure and function. Comparative phylogenetic analysis classified the R2R3-MYB TFs into 33 subfamilies. S3-7,10,12-13,21 and N4-7 were extensively involved in the metabolic process; S9,13,16-19,24-25 and N1-3,8 were associated with the growth and development of D. odorifera. Based on the differential transcriptional expression levels of R2R3-MYBs in different tissues, DodMYB32, DodMYB55, and DodMYB89 were tentatively screened for involvement in the regulatory process of heartwood. Further studies have shown that the DodMYB89, localized in the nucleus, has transcriptional activation activity and is involved in regulating the biosynthesis of the secondary metabolites of heartwood by activating the promoters of the structural genes DodI2'H and DodCOMT. This study aimed to comprehensively analyze the functions of the R2R3-MYB TFs and screen for candidate genes that might be involved in heartwood formation of D. odorifera.

Earlier onset and slower heartwood investment in faster-growing trees of African tropical species.

BACKGROUND AND AIMS: Heartwood plays an important role in maintaining the structural integrity of trees. While, its formation has long be thought to be solely driven by internal ageing processes, more recent hypotheses suggest that heartwood formation acts as a regulator of the tree water balance by modulating sapwood quantities. Testing both hypotheses would shed light on the potential ecophysiological nature of heartwood formation, a very common process in trees. METHODS: We measured heartwood and sapwood quantities, xylem conduits and growth ring width and number on 406 stems of Pericopsis elata with ages ranging from 2 to 237 years. A subset of 17 trees with similar ages but varying growth rate were sampled in a shaded (slower growth) and sun-exposed (faster growth) site. We used regression analysis and structural equations modelling to investigate the dynamics and drivers of heartwood formation. KEY RESULTS: We found a positive effect of growth rate on the probability of heartwood occurrence, suggesting an earlier heartwood onset in faster-growing stems. After this onset age, heartwood area increases with stem diameter and age. Despite the similar heartwood production per unit stem diameter increment, shaded trees produce heartwood faster than sun-exposed trees. Tree age and hydraulics showed similar direct effects on heartwood and sapwood area of sun-exposed trees, suggesting their mutual role in driving the heartwood dynamics of sun-exposed trees. However, for shaded trees, only tree hydraulics showed a direct effect, suggesting its prominent role over age in driving the heartwood dynamics in limited growing conditions. The positive relationship between growth rate and maximum stomatal conductance supports this conclusion. CONCLUSIONS: Heartwood area increases as the tree ages but at a slower rate in trees where water demand is balanced by a sufficient water supply. Our findings suggest that heartwood formation is not only a structural but also a functional process.

Genotype-Environment Interaction and Horizontal and Vertical Distributions of Heartwood for Acacia melanoxylon R.Br.

Acacia melanoxylon (blackwood) is a valuable wood with excellent-quality heartwood extensively utilized worldwide. The main aim of this study was to confirm the horizontal and vertical variation and provide estimated values of genetic gains and clonal repeatabilities for improving breeding program of A. melanoxylon. Six blackwood clones at 10 years old were analyzed in Heyuan and Baise cities in China. Stem trunk analysis was conducted for sample trees to explore the differences between heartwood and sapwood. The heartwood radius (HR), heartwood area (HA), and heartwood volume (HV) in heartwood properties decreased as tree height (H) in growth traits increased, and the HV = 1.2502 DBH (diameter at breast height)1.7009 model can accurately estimate the heartwood volume. Furthermore, G × E analysis showed that the heritabilities of the eleven indices, including DBH, DGH (diameter at ground height), H, HR, SW (sapwood width), BT (bark thickness), HA, SA (sapwood area), HV, HRP (heartwood radius percentage), HAP (heartwood area percentage), and HVP (heartwood volume percentage) were between 0.94 and 0.99, and repeatabilities of the eleven indices were between 0.74 and 0.91. Clonal repeatability of DBH (0.91), DGH (0.88), and H (0.90) in growth traits, HR (0.90), HVP (0.90), and HV (0.88) in heartwood properties were slightly higher than for SA (0.74), SW (0.75), HAP (0.75), HRP (0.75), and HVP (0.75). These data also implied that the growth characteristics of heartwood and sapwood of blackwood clones were less affected by the environment and had substantial heritability.

Axial conduit widening, tree height, and height growth rate set the hydraulic transition of sapwood into heartwood.

The size-related xylem adjustments required to maintain a constant leaf-specific sapwood conductance (KLEAF) with increasing height (H) are still under discussion. Alternative hypotheses are that: (i) the conduit hydraulic diameter (Dh) at any position in the stem and/or (ii) the number of sapwood rings at stem base (NSWr) increase with H. In addition, (iii) reduced stem elongation (ΔH) increases the tip-to-base conductance through inner xylem rings, thus possibly the NSWr contributing to KLEAF. A detailed stem analysis showed that Dh increased with the distance from the ring apex (DCA) in all rings of a Picea abies and a Fagus sylvatica tree. Net of DCA effect, Dh did not increase with H. Using sapwood traits from a global dataset, NSWr increased with H, decreased with ΔH, and the mean sapwood ring width (SWrw) increased with ΔH. A numerical model based on anatomical patterns predicted the effects of H and ΔH on the conductance of inner xylem rings. Our results suggest that the sapwood/heartwood transition depends on both H and ΔH, and is set when the carbon allocation to maintenance respiration of living cells in inner sapwood rings produces a lower gain in total conductance than investing the same carbon in new vascular conduits.

A Study of the Chemical Composition and Biological Activity of Michelia macclurei Dandy Heartwood: New Sources of Natural Antioxidants, Enzyme Inhibitors and Bacterial Inhibitors.

The wood of Michelia macclurei Dandy (MD) is an excellent material that is widely used in the furniture, handicraft, and construction industries. However, less research has been conducted on the chemical composition and biological activity of heartwood, which is the main valuable part of the wood. This study aimed to investigate the chemical composition and biological activities of the heartwood of Michelia macclurei Dandy (MDHW) and to confirm the active ingredients. Triple quadrupole gas chromatography-mass spectrometry (GC-MS) was used to characterize the volatile components of MDHW, while ultra-performance liquid chromatography-mass spectrometry was used to analyze the non-volatile components (UPLC-MS). The total reducing power, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging assays, acetylcholinesterase and α-glucosidase inhibition assays, and an antimicrobial test of 4 gram bacteria were used to describe the in vitro bioactivities. The GC-MS analysis showed that the volatile components of MDHW were mainly fatty compounds and terpenoids, with sesquiterpenes and their derivatives dominating the terpene composition. ß-elemene was the main terpene component in the steam distillation (11.88%) and ultrasonic extraction (8.2%) methods. A total of 67 compounds, comprising 45 alkaloids, 9 flavonoids, 6 lignans, and others, were found by UPLC-MS analysis. The primary structural kinds of the non-volatile components were 35 isoquinoline alkaloids. Alkaloids were the predominant active constituent in all MDHW extracts, including crude extracts, alkaloid fractions, and non-alkaloid fractions. These extracts all demonstrate some biological effects in terms of antioxidant, enzyme inhibition, and bacterial inhibition. The findings of this study show that MDHW is abundant in chemical structure types, has great bioactivity assessment, and has the potential to be used to create natural antioxidants, products that postpone Alzheimer's disease and lower blood sugar levels and antibacterial agents.