Trees最新文献

Key message

Timing of autumn phenology of birch populations does not consistently follow the latitudinal gradient but varies according to the phenophase, the scale of measurements and the current year meteorological conditions.

Abstract

Lack of knowledge on autumn phenology of deciduous trees still exists for high-latitude regions. We studied the leaf and wood growth autumn phenology of mountain birch in a sub-arctic climate (northern Sweden) and compared them with the same dynamics for silver birch in a temperate climate (southern Norway and Belgium). The first autumn phenophase for mountain birch was the decline of the remotely sensed Terrestrial Chlorophyll Index (TCI) at the end of July. This was followed by wood growth cessation, onset of chlorophyll degradation and of loss of canopy greenness, and the latter accompanied by onset of anthocyanin production and flavonoids degradation. The earlier timing of TCI decline than chlorophyll degradation was probably due to the different scales of measurements (ecosystem level vs. tree leaves, respectively). In 2020, the decline in canopy greenness started in the same period at the three studied sites, showing an unexpected early timing for Belgium, likely due to the very warm late summer conditions and drought stress or intraseasonal legacy effects. Accordingly, wood growth cessation also occurred unexpectedly earlier in Belgium than in Norway. The end of senescence was inversely related to latitude. Our study presents, for the first time, the autumn timeline of a deciduous species at the northern treeline, and indicates that the timing of autumn phenology of birch populations does not consistently follow the latitudinal gradient but varies according to the phenophase, the scale of measurements and the current year meteorological conditions.

Key message

The study reveals a significant relationship between the development of vessel elements and a reduction in the frequency of periclinal cell divisions.

Abstract

The relationship between divisional activity, the pattern of cell divisions, interactions between cambial initials, mother cells, and chosen cell types differentiating into secondary xylem remains an intriguing and largely undiscovered area. In the study we analysed the relation between vessel element development and frequency of periclinal cell divisions in the vascular cambium. Juvenile wood of temperate climate tree species differing in wood porosity type was used. Transverse sections of collected plant material were obtained, and analysed using bright field, and epifluorescence microscopy. We showed that the presence of vessel elements is related to a reduction in the number of periclinal cell divisions in radial cell files in which vessel elements were formed. With consideration for assumptions arising from the newly proposed tension stress hypothesis, we speculate that conditions enabling the enlargement of vessel elements by intrusive growth (exceeding the threshold value of radial tensile stress resulting in the separation of periclinal walls of neighbouring cells and the creation of microspaces between them) may modify the stress pattern in the area of their formation. This could lead to a change in the frequency of periclinal cell divisions within affected radial files.

Key message

We report the occurrence of blue rings in a dicotyledonous angiosperm wood and show the differences between blue rings and tension wood.

Abstract

In plant stems, local and short-term climatic factors highly influence programmed wood cell production, size, shape, wall composition and thickness. Previous analyses of conifer woods have highlighted the formation of a continuous layer of less lignified axial tracheids, the so-called blue ring. Until now, blue rings have never been described in dicotyledonous angiosperm woods. Here, we report the formation of blue rings on two Populus x canadensis clones (“Tucano” and “San Martino”), and we discuss potential causal factors related to environmental growing conditions, wood formation, and plant hormones. Blue rings were observed in all 13 poplar cuttings included in the study, with the primary driving factor identified as a lack of hormonal signalling due to apical bud and young leaf damage after intense warmth. Our analyses emphasised the strong influence of short-term events on blue ring formation, the interconnection between lignification and leaf-originating signals, and a clone-specific response to apical bud and leaf damage. Identifying blue rings in angiosperms could promote studies on plant adaptation to a changing climate and refine paleoclimate reconstructions from tree rings.

Seeds of some tree species are often consumed by vertebrates after germination, resulting in the loss of cotyledons that still contain nutrients, affecting early seedling formation. However, little attention has been given to strategies employed by seeds to address post-emergence predation. Seed nutrient transfer of Quercus variabilis was quantified after removing cotyledons at 11 times, with intervals of 5 or 10 days between them. Seedling performance in the field was evaluated at the end of the first- and second-growing seasons. Cotyledon removal on the 10th day had no significant impact on seedling survival. However, removal of cotyledon on the fifth day substantially reduced seedling survival rates, with effects lasting until the end of the second growing season. Seedling growth was not influenced by cotyledon removal after 20 days, but removal of cotyledon on day 15 resulted in a significant decrease in seedling height and ground diameter at the end of the second growing season. The percentage of residual nutrients in the cotyledons was always less than the residual biomass as nutrient transfer was rapid during the critical stages of seedling establishment. Nutrient transfer was asynchronous; transfer rate of starch was the highest, followed by K, P, and N. Rapid nutrient transfer and its asynchrony might be the regeneration strategy of Quercus seeds under predation pressure. Therefore, seeds of Quercus should be protected in the early stages of seedling establishment.

Key message

As the age of hazelnut orchards increases, the amount of fatty acid composition and bioactive compounds beneficial for health significantly decreases, therefore renewal of old hazelnut orchards is recommended. 

Abstract

This study was carried out to determine how ocak planting age affected bioactive compounds and fatty acid composition in the Tombul hazelnut cultivar. Ocak planting age (20, 30, 40, 50, and 60 years) significantly affected bioactive compounds and fatty acid composition. As ocak planting age increased, total fat, free fatty acids, oleic acid, stearic acid, antioxidant activity, total phenolic and dry matter content decreased. On the other hand, linoleic acid, linolenic acid, and palmitic acid content increased in parallel with the increase in planting age. In addition, the increase in the age of ocak affected the oleic/linoleic acid ratio and caused a decrease in this ratio in 50 and 60 years old ocaks. Correlation analysis showed a high correlation between bioactive compounds and fatty acid composition. According to the results of heatmap clustering analysis, 20, 30, 40, and 50 age groups were clustered together (A), while 60 age groups were clustered in a separate branch (B). Similarly, oil ratio, stearic acid, oleic acid, dry matter content, antioxidant activity, and total phenolic content were categorized as the first group and other components as the second group. As a result, ocak planting age significantly affected the bioactive compounds and fatty acid composition of hazelnut, which are beneficial for human health.

Key message

Deeper groundwater tables restrict taller, slenderer tree forms, pinpointing the importance of hydraulic path length presumably dictated by groundwater depth in regulating tree growth and architecture.

Abstract

How tree dimensions are interrelated (i.e., allometry) is a key question in biomechanics and forest ecology. Yet, the functional significance of tree allometry in coping with groundwater availability in drylands has been rarely explored. This gap of knowledge is particularly acute for riparian forests in Central Asia (known as Tugay forests), where groundwater table depth (GWD) is one of the most limiting factors. Based on the rationale of the hydraulic constraint hypothesis in explaining tree height growth, we posited that GWD should dictate hydraulic path length and eventually limit height (H) more than diameter (D) growth. Therefore, we predicted that there would be a lower increment in H with a unit increment in D (i.e., a small scaling exponent), or lower H at a given D, above deeper groundwater tables. Here we gathered a dataset of paired H–D measures for > 6500 trees of Populus euphratica, a keystone phreatophyte species of riparian Tugay forests, along a gradient of GWD from 1.5 m to 10 m across 16 sites in the Tarim River corridor (NW China). We quantified the H–D allometries at individual sites using standardized major axis regression, and tested for any significant shift in scaling exponents or expected H at a given D in relation to GWD. Results showed that the H–D scaling exponents in P. euphratica varied widely across sites, with an average of 0.65 (i.e., H ∝ D^0.65) close to the “canonical” value of 2/3 as posited by theory. With increasing GWD, the scaling exponents did not vary predictably, but the expected H at the grand mean of D decreased as anticipated. This study highlights the functional importance of shorter, stouter tree architectures in persisting above deeper groundwater tables within and perhaps beyond riparian forests in Central Asia’s drylands.

Key message

Evaluated tower, mast, crane, and UAV methods for forest vertical gap fraction, LAI, and CI measurements in different seasons. UAV is promising for forest vertical structural profiling.

Abstract

The vertical distribution of canopy structural parameters, such as canopy gap fraction, leaf area index (LAI) and clumping index (CI), is important for understanding the forest structural and functional properties. However, vertically distributed canopy structural data are rare, and current methods are either inefficient or costly for obtaining sufficient amounts of such data. This study conducted a series of field campaigns to obtain forest vertical structural measurements at two temperate forest sites in northern China from 2020 to 2023. Four different measurement systems were compared: (1) flux towers with accessible platforms at different heights, (2) a portable and extensible sampling mast with a digital hemispherical photography (DHP) camera attached on top, (3) a tower crane with a DHP camera fixed on the crane hook, and (4) an uncrewed aerial vehicle (UAV) with a DHP camera attached on top. The measured effective plant area index (PAI_eff) shows clearly seasonal variations at different heights. The CI remains relatively consistent at different heights, and the leaf-off value is approximately 0.1−0.2 higher than the leaf-on one. The flux tower method can be used for vertical profile measurement at a fixed location, whereas the portable mast is suitable for lower-level (< 15 m) measurement. Crane measurement requires an established facility and is useful for local measurement around the crane. UAV with an attached DHP provides a promising method for monitoring vertical structural parameters. The vertical structural profiles obtained in this study can be used in various modeling and validation studies.

Key message

The formation of resin ducts of Toxicodendron vernicifluum bark is controlled by adjusting the number and size of resin ducts with increasing age.

Abstract

Toxicodendron vernicifluum is a valuable tree species for harvesting lacquer fluid (urushi). Although resin ducts are crucial for increasing urushi production, the development of resin ducts with tree age in T. vernicifluum remains unclear. This study analyzed the characteristics of normal resin ducts in the bark using stereomicroscopy and cryo-scanning electron microscopy. The current year’s trunk already possessed numerous resin ducts beneath the sclereid cell groups. These structures were approximately connected to the outer periphery of the inner bark, suggesting that they may serve an essential defensive function in young trunks with thin outer bark. Observations of the distribution pattern of resin ducts revealed that the total area per unit length, calculated by multiplying the number of resin ducts and each area, tended to increase with tree growth in all parts of the inner bark. However, the number, and the total area per unit length in the current year-formed inner bark (assumed 200 µm from the cambium) were high in the 1–3-year-old trunks, decreased significantly in one to 4–6-year-old trunks, and then remained approximately constant as the trunks aged, although the area of each resin duct showed a slight increase. The findings suggest that T. vernicifluum bark forms a large number of resin ducts to increase the total area of resin ducts during early stage of bark development. Once the bark has developed, the formation of resin ducts is controlled by adjusting the number and size of resin ducts. Furthermore, the size of resin ducts in the outer part of the inner bark became larger than the newly formed one, likely preventing tangential rupturing as the tangential bark size increased toward the outer. These results suggest that the physical and compositional protective functions provided by resin ducts are modified and regulated as the tree grows, offering insight into the highly sophisticated survival strategies of tree species.

Key message

Root morphology and tensile strength were affected by elevation, with changes in the former showing adaptation to the environment, and changes in the latter mainly influenced by root chemical composition.

Abstract

Plant roots have absorption and anchorage functions and play important roles in plant growth and slope stability. Root morphology and mechanics are closely related to root function and are influenced by various factors. However, the impact of elevation, which encompasses a range of environmental changes, has not been fully studied. This study aimed to investigate the responses of root morphology and root mechanics to environmental changes associated with elevation and to explore the possible effects of these responses on root reinforcement. We measured the morphological properties (length, diameter, and number), tensile strength, and chemical composition (cellulose, hemicellulose, and lignin contents) of the taproots and first- and second-order roots of Lespedeza bicolor Turcz. grown at three different elevations (986, 1839, and 2716 m). The lengths of both taproots and lateral roots decreased, while the diameter of lateral roots increased with increasing elevation. Additionally, there was a significant increase in root tensile strength as elevation increased, accompanied by an increase in cellulose content and a decrease in lignin content. Root tensile strength correlated positively with cellulose content and negatively with lignin content. The morphological and mechanical properties of L. bicolor roots are significantly influenced by elevation. Roots exhibit adaptive strategies in response to environmental factors such as hydrothermal conditions and soil nutrient availability. Cellulose and lignin have a significant impact on the biomechanical properties of roots. Regarding soil reinforcement, roots at lower elevations exhibit a more advantageous morphology. Conversely, roots at higher elevations possess greater biomass and tensile strength, making them more resistant to soil erosion under extreme environmental conditions.