Tracheid Diameter Research Articles

Cross-field pitting characteristics of reaction wood in the stem wood of Pinus merkusii and Agathis loranthifolia

This research investigated and compared the pitting type, pit number (PN), and pit diameter (PD) in the cross-field of compression wood (CWD), lateral wood (LWD), and opposite wood (OWD) in stem wood of Pinus merkusii and Agathis loranthifolia growing in Indonesia. Identification and quality evaluation were done using optical and scanning electron microscopy. A piceoid pit type was observed in the CWD of both species. The LWD and OWD of P. merkusii showed window-like and pinoid pits, whereas those of A. loranthifolia showed taxodioid and cupressoid pits. The PN and PD were the smallest in CWD of both species. In P. merkusii, LWD and OWD showed similar PN values, and PN in all parts increased from the pith to the bark. In A. loranthifolia, LWD had higher PN than in OWD, and PN in CWD and LWD decreased from near the pith to the bark, whereas in OWD, it increased. All parts of P. merkusii and CWD and OWD of A. loranthifolia showed a positive correlation between PN and radial tracheid diameter, whereas LWD showed a negative correlation. In P. merkusii, the PD of LWD approximated that of OWD, whereas, in A. loranthifolia, LWD had a larger PD than that exhibited by OWD.

The response of physiological and xylem anatomical traits under cadmium stress in Pinus thunbergii seedlings.

Studying the response of physiological and xylem anatomical traits under cadmium stress is helpful to understand plants' response to heavy metal stress. Here, seedlings of Pinus thunbergii Parl. were treated with 50, 100 and 150mg kg-1 Cd2+ for 28days. Cadmium and nonstructural carbohydrate content of leaves, stems and roots, root Cd2+ flux, cadmium distribution pattern in stem xylem and phloem, stem xylem hydraulic traits, cell wall component fractions of stems and roots, phytohormonal content such as abscisic acid, gibberellic acid 3, molecule -indole-3-acetic acid, and jasmonic acid from both leaves and roots, as well as xylem anatomical traits from both stems and roots were measured. Root Cd2+ flux increased from 50 to 100mmol L-1 Cd2+ stress, however it decreased at 150mmol L-1 Cd2+. Cellulose and hemicellulose in leaves, stems and roots did not change significantly under cadmium stress, while pectin decreased significantly. The nonstructural carbohydrate content of both leaves and stems showed significant changes under cadmium stress while the root nonstructural carbohydrate content was not affected. In both leaves and roots, the abscisic acid content significantly increased under cadmium stress, while the gibberellic acid 3, indole-3-acetic acid and jasmonic acid methylester content significantly decreased. Both xylem specific hydraulic conductivity and xylem water potential decreased with cadmium stress, however tracheid diameter and double wall thickness of the stems and roots were not affected. High cadmium intensity was found in both the stem xylem and phloem in all cadmium stressed treatments. Our study highlighted the in situ observation of cadmium distribution in both the xylem and phloem, and demonstrated the instant response of physiological traits such as xylem water potential, xylem specific hydraulic conductivity, root Cd2+ flux, nonstructural carbohydrate content, as well as phytohormonal content under cadmium stress, and the less affected traits such as xylem anatomical traits, cellulose and hemicellulose.

The effect of fire on tree-ring width and tracheid dimensions of Pinus nigra

Summary Forest fires play a significant role in the growth and development of trees because they can damage the phloem and cambium. Fire injury induces the formation of fire scars that can cause xylem dysfunction. The study area is located in Taşköprü, Kastamonu (Western Black Sea of Turkiye), where two forest fires occurred in 1957 and 2020. In this study, the effect of the 1957 fire on the tree-ring widths and tracheid dimensions of Pinus nigra trees was investigated. We measured tree-ring widths and tracheid dimensions of fire-scarred (FS) and unscarred (UF) trees during four different periods: the pre-fire period (1947–1956), fire event year (1957), and post–fire periods (1958–1967 and 2011–2020). In this study, UF trees showed almost 2.5–3 times wider tree–ring widths (TRWs) than FS trees. FS and UF trees also showed great variation in tracheid dimensions in the four different periods; the average tracheid diameter (TD), lumen area (TLA), and wall thickness (TWT) values increased significantly in UF trees compared to FS trees during the fire event and post-fire periods. The average TD, TLA, and average tracheid lumen diameter (TLD) decreased during the fire and post-fire years in the FS trees. In this study, we suggest that fire injury significantly affects the tracheid dimensional traits of FS Pinus nigra trees. Our results also suggest that although Pinus nigra trees experienced serious fire damage, they continued to grow but with a decrease in tracheid size.

Coordination of pinna, petiole, and root anatomical traits in 24 tropical-subtropical fern species.

Ferns are primitive vascular plants with diverse morphologies and structures. Plant anatomical traits and their linkages can reflect adaptation to the environment; however, these remain are still poorly understood in ferns. The main objective of this study was to explore whether there was structural coordination among and within organs in fern species. We measured 16 hydraulically related anatomical traits of pinnae, petioles, and roots of 24 representative fern species from the tropical and subtropical forest understory and analyzed trait correlation networks. In addition, we examined phylogenetic signals for the anatomical traits and analyzed co-evolutionary relationships. These results indicated that stomatal density and all petiole anatomical traits exhibited significant phylogenetic signals. Evolutionary correlations were observed between the tracheid diameter and wall thickness of the petiole and between the water transport capacity of the petiole and stomatal density. Conversely, anatomical traits of roots (e.g., root diameter) showed no phylogenetic signals and were not significantly correlated with those of the pinnae and petioles, indicating a lack of structural coordination between the below- and above-ground organs. Unlike angiosperms, vein density is unrelated to stomatal density or pinna thickness in ferns. As root diameter decreased, the cortex-to-stele diameter ratio decreased significantly (enhanced water absorption) in angiosperms but remained unchanged in ferns. These differences lead to different responses of ferns to climate change and improve our knowledge of the water adaptation strategies of ferns.

Xylem plasticity of root, stem, and branch in Cunninghamia lanceolata under drought stress: implications for whole-plant hydraulic integrity.

A better understanding of xylem hydraulic characteristics in trees is critical to elucidate the mechanisms of forest decline and tree mortality from water deficit. As well as temperate forests and forests growing in arid regions, subtropical and tropical forests are also predicted to experience an increased frequency and intensity of climate change-induced drought in the near future. In this study, 1-year-old Cunninghamia lanceolata seedlings (a typical subtropical species in southern China) were selected for a continuous controlled drought pot experiment of 45 days duration. The experimental treatments were non-drought (control), light drought, moderate drought and severe drought stress, which were 80%, 60%, 50%, and 40%, respectively of soil field maximum moisture capacity. The hydraulic conductivity, specific conductivity and water potential of roots, stems, and branches of C. lanceolata all decreased with the prolonging of drought in the different drought intensities. The relative decrease in these hydraulic values were greater in roots than in stems and branches, indicating that roots are more sensitive to drought. Root tracheid diameters normally reduce to ensure security of water transport with prolonged drought, whilst the tracheid diameters of stems and branches expand initially to ensure water transport and then decrease to reduce the risk of embolism with continuing drought duration. The pit membrane diameter of roots, stems and branches generally increased to different extents during the 15-45 days drought duration, which is conducive to enhanced radial water transport ability. The tracheid density and pit density of stems generally decreased during drought stress, which decreased water transport efficiency and increased embolism occurrence. Correlation analysis indicated that anatomical plasticity greatly influenced the hydraulic properties, whilst the relationships varied among different organs. In roots, tracheid diameter decreased and tracheid density increased to enhance water transport security; stems and branches may increase tracheid diameter and pit membrane diameter to increase hydraulic conductivity ability, but may increase the occurrence of xylem embolism. In summary, under drought stress, the xylem anatomical characteristics of C. lanceolata organs were highly plastic to regulate water transport vertically and radially to maintain the trade-off between hydraulic conductivity efficiency and safety.

The phenotypic and genetic effects of drought-induced stress on wood specific conductivity and anatomical properties in white spruce seedlings, and relationships with growth and wood density.

Drought frequency and intensity are projected to increase with climate change, thus amplifying stress on forest trees. Resilience to drought implicates physiological traits such as xylem conductivity and wood anatomical traits, which are related to growth and wood density. Integrating drought-stress response traits at the juvenile stage into breeding criteria could help promote the survival of planted seedlings under current and future climate and thus, improve plantation success. We assessed in greenhouse the influence of drought-induced stress on 600 two-year-old white spruce (Picea glauca) seedlings from 25 clonal lines after two consecutive growing seasons. Three levels of drought-induced stress were applied: control, moderate and severe. Seedlings were also planted at a 45° angle to clearly separate compression from normal wood. We looked at the phenotypic and genetic effects of drought stress on xylem specific hydraulic conductivity, lumen diameter, tracheid diameter and length, and the number of pits per tracheid in the normal wood. We detected no significant effects of drought stress except for tracheid length, which decreased with increasing drought stress. We found low to high estimates of trait heritability, which generally decreased with increasing drought stress. Genetic correlations were higher than phenotypic correlations for all treatments. Specific conductivity was genetically highly correlated positively with lumen diameter and tracheid length under all treatments. Tracheid length and diameter were always negatively correlated genetically, indicating a trade-off in resource allocation. Moderate to high genetic correlations sometimes in opposite direction were observed between physico-anatomical and productivity traits, also indicating trade-offs. A large variation was observed among clones for all physico-anatomical traits, but clonal ranks were generally stable between control and drought-induced treatments. Our results indicate the possibility of early screening of genetic material for desirable wood anatomical attributes under normal growing conditions, thus allowing to improve the drought resilience of young trees.

A comparative study on quantitative anatomical characteristics of compression, lateral, and opposite woods in Agathis loranthifolia and Pinus merkusii

Quantitative anatomical characteristics and their radial variation in compression (COW), lateral (LAW), and opposite (OPW) woods of Agathis loranthifolia and Pinus merkusii stem woods growing in Indonesia were observed and compared to understand wood quality. The length, diameter, wall thickness, and lumen diameter of tracheids and ray height and numbers were observed using optical microscopy. In both species, COW had the shortest tracheid length, smallest tracheid and lumen diameter, thickest cell wall, and highest ray numbers among the parts, while LAW and OPW showed comparable or variable values in quantitative characteristics. In A. loranthifolia, COW had the highest ray height, whereas, in P. merkusii, it had the lowest uniseriate and fusiform ray heights. No significant difference was observed in ray numbers and heights between LAW and OPW. In both species, the tracheid length and lumen-to-diameter ratio in COW, LAW, and OPW tended to increase from near the pith to near the bark while the wall-to-diameter ratio decreased. The ray heights of all parts increased with increasing distance from the pith, whereas the ray number decreased.

The three-dimensional distribution of bordered pits across growth rings of stem segment in Platycladus orientalis (Cupressaceae) seedlings

Summary The dimensions and distribution pattern of bordered pits are critical to the xylem water transport function of trees. However, studies on the three-dimensional distribution pattern of pits across xylem growth rings are still limited. Here, Micro-Computed Tomography (Micro-CT) was used to acquire xylem images of two-year-old Platycladus orientalis seedlings. We analyzed the tracheid lumen diameter of 665 tracheids, pit volume, and pit diameter of 11 810 inter-tracheid pits from three radial profiles. The volume ratio of inter-tracheid pits was about 0.90–0.96%. The average pit diameter was 6.8 μm and the average pit volume was 58.9 μm3, and more than 80% of the pits had a diameter of 5–8 μm and a volume of 20–90 μm3. Both the pit diameter and the pit volume increased gradually in the radial direction from the second-year growth ring to the current-year growth ring, and the pit diameter and volume were significantly higher in earlywood than in latewood. The distribution pattern of the tracheid diameter was similar to that of the pit diameter, and the wider the tracheids, the larger the pits. The distribution of bordered pits in P. orientalis may be a critical trait explaining the xylem embolism spread pattern in this species.

Adaptive strategies to freeze-thaw cycles in branch hydraulics of tree species coexisting in a temperate forest

Freeze-thaw cycles (FTCs) limit the distribution and survival of temperate tree species. Tree species with different wood types coexist in temperate forests and are subjected to the same FTCs. It is essential to understand how these trees differentially cope with xylem hydraulic failure induced by FTCs in the field. The branch hydraulic traits and nonstructural carbohydrate concentration of six coexisting tree species in a temperate forest were measured from mid-winter to early spring when the FTCs occurred from January to April. The percentage loss of hydraulic conductivity (PLC) was lower, and the water potential inducing a 50% loss of hydraulic conductivity (P50) was more negative in tracheid trees than in ring- and diffuse-porous trees, suggesting tracheid trees with narrow tracheid diameters showed less vulnerable to embolism and provided a lower degree of hydraulic failure during FTCs (stronger resistance). Ring-porous trees always showed lower hydraulic conductivity and higher PLC and P50, and these traits did not change during FTCs, suggesting that they might lose the hydraulic functions in winter and abandon the last year xylem. The P50 in diffuse-porous increased after several FTCs (frost fatigue), but that in tracheid species continued to increase (or even decrease) until the end of FTCs (69 cycles), suggesting that tracheid trees were less sensitive to frost fatigue than diffuse-porous trees. Soluble sugar concentration in deciduous trees negatively correlated with PLC at the end of FTCs, indicating that the effect of soluble sugar on refilling embolism occurred in early spring. While the soluble sugar concentration of deciduous trees decreased, that of two evergreen tracheid trees gradually increased, possibly due to the winter photosynthesis of evergreen leaves. Our results suggest temperate trees adopt different strategies to cope with the same FTCs. These findings enrich the understanding of plant hydraulics and carbon physiology in winter and provide insights into the response of different species coexisting in temperate forests under climate change.

Atypical tracheid organization in proximal wood of late Palaeozoic Sigillaria approximata Fontaine et White (Lycopsida)

Abstract It is thought that arborescent lycopsid cambial expansion kept pace with radial wood growth via tangential broadening of the fusiform initials, resulting in progressive outward expansion in tracheid diameters and an absence of de novo tracheid files. This pattern appears in distal lycopsid axes but has not been investigated in proximal-most trunk vasculature where wood was thickest and primary xylem thinnest. Here, a ground-level trunk vasculature fossil of Sigillaria approximata in transverse section is described. This proximal vasculature diverges from the expectations of the current lycopsid wood production model in two main ways: first, inner and outer wood tracheids have approximately the same lumen diameters, such that there is no trend towards centrifugally increasing lumen diameters; and second, de novo cell files commonly appear within the wood. The outwards rate of cambial circumference expansion closely tracks the outwards rate of new wood tracheid file appearance, suggesting that the addition of new files is the primary way the cambium expanded proximally. Because this vasculature can only be studied in transverse section, the developmental mode producing new files cannot be determined. However, evidence from this specimen is sufficient to demonstrate that arborescent lycopsid wood production was more complex than previously understood.

Anatomical characteristics of the leaning stem in Pinus merkusii seedling

Abstract. Safitri NM, Prastiwi FW, Salsabila S, Feriawan Y, Brilianto A, Nugroho WD. 2023. Anatomical characteristics of the leaning stem in Pinus merkusii seedling. Biodiversitas 24: 3796-3802. Pinus merkusii Jungh. & de Vriese is one of the tropical conifer species. The species formed reaction wood called compression wood (CW) when the stem grows in an abnormal position. CW in stem wood is frequently found to cause several problems for utilization in the use of its products. However, there are few studies on the anatomical characteristics of reaction wood in tropical conifer. This study aimed to observe the differences in anatomical characteristics between compression (CW) and opposite (OW) woods in leaning the stem of P. merkusii seedlings and their anatomical differences compared to normal wood (NW). Approx. 1-year-old P. merkusii seedlings from a nursery in Trenggalek, East Java, Indonesia, that were naturally bent or tilted were used in the study. Anatomical characteristics of wood, namely the dimension of tracheids, rays, resin canals, and the proportion of cells were observed in the study. The results showed that CW of P. merkusii seedlings formed a rounded tracheid shape and intercellular space. The differences between CW and OW in P. merkusii seedlings were significant in terms of height of ray cells, tracheid proportion, and resin canal proportion. However, tracheid length, tracheid diameter, tracheid wall thickness, resin canal diameter and frequency, rays frequency, and ray proportion were not significantly different compared to OW and NW.

Influence of the abiotic environment on Permian woods from northwestern Gondwana

Fluctuations in cell densities are common in the secondary xylem of gymnosperms from the lower Permian of Maranhão, northeastern Brazil, but they lack any distinct annual growth ring. Although the region was under a subtropical arid climate, sedimentary sequences of the Pedra de Fogo Formation indicate that plants inhabited the shores of large lakes, ensuring sufficient moisture for continuous growth of diverse flora. Therefore, the presence of acyclical tree rings would be due to oscillations in the base level of adjacent lakes, occasioned by short periods of drought or flood. Even so, cell-to-cell variation of tracheid diameters was quantified through mean sensitivity, showing that environmental conditions are similar in the two paleobotanical sites analyzed. However, gymnosperms whose piths have canals, ducts, septa or lacunae exhibit a higher mean sensitivity, showing that such plants inhabited areas of greater water stress or have increased sensitivity to environmental disturbances. The effect of defoliation and biotic interactions is also presumed to have affected the cambial activity. Localized and concentric shear bands are features identified in several samples, indicating that the pressure of sediments on the woods resulted in non-axial plastic deformation during the burial.

A reduced role for water transport during the Cenozoic evolution of epiphytic Eupolypod ferns.

The Cretaceous-Cenozoic expansion of tropical forests created canopy space that was subsequently occupied by diverse epiphytic communities including Eupolypod ferns. Eupolypods proliferated in this more stressful niche, where lower competition enabled the adaptive radiation of thousands of species. Here, we examine whether xylem traits helped shape the Cenozoic radiation of Eupolypod ferns. We characterized the petiole xylem anatomy of 39 species belonging to the Eupolypod I and Eupolypod II clades occupying the epiphytic, hemiepiphytic, and terrestrial niche, and we assessed vulnerability to embolism in a subset of species. The transition to the canopy was associated with reduced xylem content and smaller tracheid diameters, but no differences were found in species vulnerability to embolism and pit membrane thickness. Phylogenetic analyses support selection for traits associated with reduced water transport in Eupolypod 1 species. We posit that in Eupolypod epiphytes, selection favored water retention via thicker leaves and lower stomatal density over higher rates of water transport. Consequently, lower leaf water loss was coupled with smaller quantities of xylem and narrower tracheid diameters. Traits associated with water conservation were evident in terrestrial Eupolypod 1 ferns and may have predisposed this clade toward radiation in the canopy.

Influence of Four Spacings between Trees and Four Samplings Heights on Selected Wood Quality Attributes of White Spruce (Picea glauca (Moench) Voss)

Four Picea glauca (Moench) Voss trees grown at each of four square spacing intensities between trees: 1.2 m, 1.8 m, 4.3 m, and 6.1 m in a plantation established in 1967 in the Petawawa Research Forest, Ontario, Canada (lat. 45.59° N, long. 77.25° W, elev. 168 m) and sampled at four different heights (1.3 m, 4.3 m, 7.3 m, 10.3 m) were used to study the impact of spacing between trees and sampling height on nine wood quality attributes (ring width, ring density, tracheid length, tracheid diameter, latewood proportion, intra-ring density variation, ring area, earlywood width, and latewood width). In the juvenile wood, ring width was wider and ring density higher than in the mature wood. Tracheid length was longer and tracheid diameter wider in the mature wood compared to the juvenile wood. The variation of ring density between the two wood zones was limited, and latewood proportion did not show any difference with wood zone. Sampling height induced variation in more wood quality attributes than did spacing. Except for growth rate, spacing between trees did not significantly impact wood quality attributes. Most of these variations were registered between widely different spacings.

Intraspecific variation in growth‐related traits—from leaf to whole‐tree—in three provenances of Cryptomeria japonica canopy trees grown in a common garden

AbstractTo elucidate the physiological and morphological factors underlying intraspecific variation in growth rate, we examined the variation in leaf and whole‐tree traits for three geographical variations of ca. 45‐year‐old Japanese cedar (Cryptomeria japonica D. Don) with contrasting heights and radial growth in a common garden. Traits that reflect leaf‐level photosynthesis, water relations, and whole‐tree level crown structure in relation to light use and hydraulic architecture were measured. Overall, intraspecific variation in growth characteristics in field‐grown adult trees was regulated by whole‐tree properties rather than leaf properties. Most leaf traits were similar among provenances. Nevertheless, the leaf traits exhibited highest maximum net photosynthetic rate, dark respiration rate, and light compensation point in provenances whose native habitats are most similar to the common garden in the present study. Together with previous reports that this provenance has higher root nutrient acquisition capacity than the other two provenances, it can be said that organ‐level resource use strategies are coupled in a tandem manner. At the whole‐tree level, hydraulic architecture—as explained by axial variation in the hydraulically weighted tracheid diameter—can be linked to leaf distribution with respect to light use strategies as well as water transport capacity, leading to differences in growth characteristics among provenances. The study of intraspecific variation in growth characteristics in trees with a wide range of native habitats is expected to be a useful indicator for predicting changes in growth potential and forest dynamics in response to climate change in each habitat.

Relationships Between Wood-Anatomical Features and Resistance Drilling Density in Norway Spruce and European Beech

Environmental conditions affect tree-ring width (TRW), wood structure, and, consequently, wood density, which is one of the main wood quality indicators. Although studies on inter- and intra-annual variability in tree-ring features or density exist, studies demonstrating a clear link between wood structure on a cellular level and its effect on wood density on a macroscopic level are rare. Norway spruce with its simple coniferous structure and European beech, a diffuse-porous angiosperm species were selected to analyze these relationships. Increment cores were collected from both species at four sites in Slovenia. In total, 24 European beech and 17 Norway spruce trees were sampled. In addition, resistance drilling measurements were performed just a few centimeters above the increment core sampling. TRW and quantitative wood anatomy measurements were performed on the collected cores. Resistance drilling density values, tree-ring (TRW, earlywood width–EWW, transition-TWW, and latewood width–LWW) and wood-anatomical features (vessel/tracheid area and diameter, cell density, relative conductive area, and cell wall thickness) were then averaged for the first 7 cm of measurements. We observed significant relationships between tree-ring and wood-anatomical features in both spruce and beech. In spruce, the highest correlation values were found between TRW and LWW. In beech, the highest correlations were observed between TRW and cell density. There were no significant relationships between wood-anatomical features and resistance drilling density in beech. However, in spruce, a significant negative correlation was found between resistance drilling density and tangential tracheid diameter, and a positive correlation between resistance drilling density and both TWW + LWW and LWW. Our findings suggest that resistance drilling measurements can be used to evaluate differences in density within and between species, but they should be improved in resolution to be able to detect changes in wood anatomy.

Hydraulics and non-structural carbohydrate contents of Ginkgo biloba under different environmental conditions in Shenyang City, China.

Ginkgo biloba is an important urban ornamental tree species, but poor growth and damages often occur in urban environments. As a street tree species, the decline and death of G. biloba is particularly frequent, with the relevant physiological mechanism being unclear. In this study, we compared hydraulic characteristics, non-structural carbohydrate (NSC) contents and health status between G. biloba trees growing along the streets and those in parks in Shenyang City. The results showed that G. biloba growing along the streets showed higher degrees of branch and leaf mortality than those growing in the parks. Branches of G. biloba growing in both conditions showed lower degrees of xylem embolism. Branch hydraulic vulnerable curves of G. biloba under the two growing conditions also showed no significant difference, with the average P50 being lower than -2.8 MPa. G. biloba growing along the streets had lower leaf area specific conductivity, smaller tracheid diameter, smaller hydraulic diameter, lower soluble sugar content and total NSC than those growing in parks. Hydraulic failure was not the direct reason for the decline and mortality of G. biloba growing along streets. Under the more stressed growth conditions along the streets, G. biloba had smaller tracheid diameters in stems and lower Huber values, which limited the ability of water transport and photosynthetic carbon assimilation at the whole branch level. In addition, in order to deal with more serious stress such as greater heat and drought stresses, G. biloba might need to invest more NSC to repair damage, which further decreaded NSC contents in branches and increased the risk of carbon imbalance. At the same habitat (street or park), xylem hydraulics and NSC contents of G. biloba also showed relatively large difference among sampling sites, which reflected large heterogeneity of urban environment for tree growth.

Variation in Tracheid Dimensions of Conifer Xylem Reveals Evidence of Adaptation to Environmental Conditions.

Globally distributed extant conifer species must adapt to various environmental conditions, which would be reflected in their xylem structure, especially in the tracheid characteristics of earlywood and latewood. With an anatomical trait dataset of 78 conifer species growing throughout China, an interspecific study within a phylogenetic context was conducted to quantify variance of tracheid dimensions and their response to climatic and soil conditions. There was a significant difference in tracheid diameter between earlywood and latewood while no significant difference was detected in tracheid wall thickness through a phylogenetically paired t-test. Through a phylogenetic principle component analysis, Pinaceae species were found to be strongly divergent in their tracheid structure in contrast to a conservative tracheid structure in species of Cupressaceae, Taxaceae, and Podocarpaceae. Tracheid wall thickness decreased from high to low latitudes in both earlywood and latewood, with tracheid diameter decreasing for latewood only. According to the most parsimonious phylogenetic general least square models, environment and phylogeny together could explain about 21∼56% of tracheid structure variance. Our results provide insights into the effects of climate and soil on the xylem structure of conifer species thus furthering our understanding of the trees’ response to global change.

Insight Into the Multiple Branches Traits of a Mutant in Larix olgensis by Morphological, Cytological, and Transcriptional Analyses.

Larix olgensis is a tall deciduous tree species that has many applications in the wood fiber industry. Bud mutations are somatic mutations in plants and are considered an ideal material to identify and describe the molecular mechanism of plant mutation. However, the molecular regulatory mechanisms of bud mutations in L. olgensis remain unknown. In this study, dwarfed (or stunted), short-leaved, and multi-branched mutants of L. olgensis were found and utilized to identify crucial genes and regulatory networks controlling the multiple branch structure of L. olgensis. The physiological data showed that the branch number, bud number, fresh and dry weight, tracheid length, tracheid length-width ratio, inner tracheid diameter, and epidermal cell area of mutant plants were higher than that of wild-type plants. Hormone concentration measurements found that auxin, gibberellin, and abscisic acid in the mutant leaves were higher than that in wild-type plants. Moreover, the transcriptome sequencing of all samples using the Illumina Hiseq sequencing platform. Transcriptome analysis identified, respectively, 632, 157, and 199 differentially expressed genes (DEGs) in buds, leaves, and stems between mutant plants and wild type. DEGs were found to be involved in cell division and differentiation, shoot apical meristem activity, plant hormone biosynthesis, and sugar metabolism. Furthermore, bZIP, WRKY, and AP2/ERF family transcription factors play a role in bud formation. This study provides new insights into the molecular mechanisms of L. olgensis bud and branch formation and establishes a fundamental understanding of the breeding of new varieties in L. olgensis.

Tracheid and Pit Dimensions Hardly Vary in the Xylem of Pinus sylvestris Under Contrasting Growing Conditions.

Maintaining sufficient water transport via the xylem is crucial for tree survival under variable environmental conditions. Both efficiency and safety of the water transport are based on the anatomical structure of conduits and their connections, the pits. Yet, the plasticity of the xylem anatomy, particularly that of the pit structures, remains unclear. Also, trees adjust conduit dimensions to the water transport distance (i.e., tree size), but knowledge on respective adjustments in pit dimensions is scarce. We compared tracheid traits [mean tracheid diameter d, mean hydraulic diameter dh, cell wall reinforcement (t/b)2], pit dimensions (diameters of pit aperture Da, torus Dt, margo Dm, and pit border Dp), and pit functional properties (margo flexibility F, absolute overlap Oa, torus overlap O, and valve effect Vef) of two Scots pine (Pinus sylvestris L.) stands of similar tree heights but contrasting growth rates. Furthermore, we analyzed the trends of these xylem anatomical parameters across tree rings. Tracheid traits and pit dimensions were similar on both sites, whereas Oa, O, and F were higher at the site with a lower growth rate. On the lower growth rate site, dh and pit dimensions increased across tree rings from pith to bark, and in trees from both sites, dh scaled with pit dimensions. Adjusted pit functional properties indicate slightly higher hydraulic safety in trees with a lower growth rate, although a lack of major differences in measured traits indicated overall low plasticity of the tracheid and pit architecture. Mean hydraulic diameter and pit dimension are well coordinated to increase the hydraulic efficiency toward the outer tree rings and thus with increasing tree height. Our results contribute to a better understanding of tree hydraulics under variable environmental conditions.