Trees最新文献

Key message

We propose an improved exponential equation for the nonlinear dependence of cell measurements on the seasonal cell production in conifer wood. These changes shall simplify the model towards ease in understanding, interpretation and analysis.

Abstract

With methodological development, quantitative parameters of wood cellular structure have featured as dendroclimatic indicators in various studies. But to disentangle climatic impacts in different wood anatomical characteristics, relationships between them have to be described quantitatively and extricated. This study investigates exponential description of the non-linear dependences of conifer wood cell measurements on their seasonal production in cambial zone. Improvement to the equation of exponential model was suggested, simplifying the interpretation and analysis and providing biological meaning to all numerical parameters of the model. This new equation was demonstrated for 630 tree rings from 20 to 40-year-old trees of Siberian spruce (Picea obovata Ledeb.) in Siberia, collected at the experimental plantation, as well as for its subsets from plots of various planting density, demonstrating plausible value of the new proposed numerical parameter of model and dependence of the other parameter on the stand density, probably based on the tree height. Limitation for successful fitting of this exponential model was demonstrated, based on representativity of wide and narrow rings within sample; we proposed possible way to overcome it in certain cases.

Key message

Tree-ring shapes of the six studied coniferous species tend to be bilaterally symmetrical, and the superellipse equation is sufficient to describe the tree-ring boundaries and estimate the basal area increment.

Abstract

In nature, under environmental pressures, such as wind, slope, water availability, etc., tree-ring shapes in most cases appear to be elliptical rather than circular. Compared with the ellipse equation, the superellipse equation includes an additional parameter that allows the generation of a larger range of geometries: hypoellipse, ellipse, and hyperellipse. The more complex Gielis equation can generate asymmetrical shapes. In the present study, we modeled the geometries of tree-rings for six coniferous species using the superellipse equation (i.e., the three-parameter model) and the more complex Gielis equation (i.e., the five-parameter model). The species-specific mean value of n approached 2 and the k-value was lower than 1, which confirmed that most tree-ring shapes of the studied coniferous species were closer to an ellipse rather than a circle. However, based on superellipse equation the n-value and k-value both showed an inter-annual fluctuation that ranged between 1.75–2.25 and 0.82–1.00, respectively. This suggests that most samples of tree-rings did not follow the typical ellipse equation, but the superellipse equation. Although the Gielis equation is slightly better in the goodness of fit than the superellipse equation, 86.67% of the percent errors (PEs) of RMSE_adj between these two equations were smaller than 5%, which means that the superellipse equation is better given the trade-off between the model structural complexity and goodness of fit. Most tree-ring shapes tend to be bilaterally symmetrical, and the three-parameter superellipse equation was verified to fit the tree-ring boundaries and estimate the inter-annual increments of tree-ring area well.

Trees in private yards are subject to a complex assortment of interacting ecological, social, cultural and economic factors, including individual preferences, social networks, multiple stakeholders and social constraints. This study explored residents’ attitudes towards yard trees in China and determined the social factors shaping yard trees and yard tree planting. Nearly 300 questionnaires were collected in-person and online in urban and rural villages and communities in Zhoukou city, Henan. Most trees planted in yards were intentionally planted. Yard size was the main constraint on the number of trees in a yard with respondents repeatedly citing the lack of space as a deterrent to planting trees or planting more trees. The most popular attributes for trees planted in yards were symbolism and edibility. Residents’ attitudes were based upon tree functions. The willingness and attitudes of residents towards yard trees suggested that an increase in yard trees would be supported by residents, who appeared to be yearning for a green living environment. However, a lack of preference found for native species suggests a challenging future for native trees in yards in regard to their role in biodiversity and habitat formation. Men played the dominant role in activities associated with yard trees. Residents were keen to aid wider ambitions for greening through their own tree planting in yards, but need guidance via policies and incentives. Such moves at high levels of government will assist the achievement of sustainable development goals in the future China, such as increased city canopy and carbon targets.

Key message

Red cedar chlorophyll fluorescence remains high during the nongrowing season, while transpiration is reduced.

Abstract

Evergreen trees retain their leaves during the winter and thus can photosynthesize when conditions permit. Eastern red cedar (Juniperus virginiana) is widely distributed in the eastern USA and is known to transpire and photosynthesize outside of the growing season. However, most recent work has been done in the Great Plains, which red cedar has recently invaded, while little work has been done in its original range. I hypothesized that red cedar would behave like other conifers from summer drought-free areas and show reduced chlorophyll fluorescence and transpiration during the winter. Four red cedar trees at a site near the Ohio River in Kentucky were equipped with Granier sap flow probes, while solar irradiance, temperature, relative humidity, and soil volumetric water content (VWC) were measured at the site. Dark chlorophyll fluorescence (F_v/F_m) was measured on northern and southern aspects on an approximately weekly basis from early 2019 through mid 2021. High values of F_v/F_m were measured in both growing (April-September) and nongrowing (October-March) seasons; median values in the nongrowing season were 94% of those in the growing season, which did not support my hypothesis. F_v/F_m data were fit to a Michaelis–Menten curve that used minimum temperature of the previous two nights, aspect, and maximum irradiance on the day of measurement taken before fluorescence was measured. Sap flow was explained by maximum daily temperature, vapor pressure deficit (VPD), mean daily irradiance, and VWC. Sap flow in the nongrowing season was 74% of that seen in the growing season, due to lower values of temperature, VPD, and irradiance, supporting my hypothesis. Thus, red cedar remains physiologically active during the nongrowing season. However, it does not appear to behave like other conifers from summer drought-free areas.

Gibberellin (GA) and cytokinin (CK) signaling play antagonistic roles in leaf development and secondary plant growth. In the current study, we investigated the effects of changes in the balance of CKs and GAs on the development and leaf and stem morpho-anatomy of Delonix regia (Bojer ex. Hook.) Raf. seedlings. The balance of CKs and GAs was modified by the exogenous application of plant growth regulators (PGRs), individually or in combination. After 30 days of daily PGR applications, the growth and the morpho-anatomy of the leaf and stem were assessed. CKs and GAs have antagonistic effects on the development of D. regia. Seedlings treated with GA showed a significant increase in height, while the application of CK led to greater formation of axillary shoots, altering the architecture of the plants. GA inhibited almost all CK responses, although a negative reciprocal interaction was observed in some growth parameters. The treatments in which GA was applied showed an increase in leaf length. However, these plants presented a reduction in leaf tissue thickness and the stem cambial band. In contrast, plants treated with CK and paclobutrazol had thicker leaf blades and more prominent radial growth of the stem, with a higher proportion of secondary xylem. Our results suggest a mutual antagonistic interaction between GA and CK in D. regia and contribute to understanding how the balance between these two classes of phytohormones modulates the structure and development of plant lateral organs.

In some angiosperm species, especially in the Malvaceae family, postural control and directional growth of the stem are enabled by the mechanical interaction between the growing cambium and the secondary phloem. A key feature of this motor mechanism is the ability to redirect the tangential stress induced in secondary phloem into a longitudinal stress enabling the control of stem orientation. Here we studied how the microstructure of the secondary phloem is optimized for this function. We measured the longitudinal-tangential Poisson’s ratio and the longitudinal modulus of elasticity of secondary phloem in 22 tree species including Malvaceae and other families. We modeled the microstructure of Malvaceae secondary phloem using finite elements. The Poisson’s ratio of secondary phloem from Malvaceae trees was found one to two orders of magnitude higher than for other species, reaching the highest values ever reported for a natural material. Mechanical modeling confirmed these results and showed that parameters of the microstructure of secondary phloem are set at value optimizing this Poisson’s ratio. This highlights that the specific microstructure of Malvaceae secondary phloem is designed to maximize the conversion of cambial growth pressure into a longitudinal mechanical stress enabling the directional growth.

Key message

Flexure wood formation is not systematically observed as a part of thigmomorphogenetic syndrome induced by wind. Its formation depends likely on the dose of mechanical signal perceived and the tree size-dependent strategy to resist wind loads.

Abstract

Formation of a specific wood tissue called flexure wood often accompanies the thigmomorphogenetic syndrome in mechanically stimulated trees. Flexure wood exhibits high microfibril angle allowing for increase in the stem flexibility and higher resistance to post-elastic damage during repeated loadings. In this study, we examine the microstructure and the properties of wood produced by beech poles submitted to increased mechanical stimulus. Contrary to previous results obtained on poplar saplings, aside a little decrease in density no changes in the microstructure or the post-elastic properties of wood were observed in beech poles. While in saplings wood properties explained 25% of the resistive moment increase and 50% of the maximal curvature decrease, their relative contribution was of 6% for the resistive moment and 5% for the maximal curvature decrease in beech poles. These apparent discrepancies between our results and previous studies were explained by a possible combination of three factors: (i) experienced level of mechanical stimulus, (ii) tree size-dependent shift in the strategy to resist wind loads and (iii) the species sensitivity to thigmomorphogenetic syndrome. We further suggest the use of juvenile transition as an indicator of the species strategy to cope with environmental signals adopting a broader view of the adaptive capacity of a given species.

Pisonia grandis R. Br. is a tree commonly found in urban coastal and tropical regions, valued for its ornamental beauty and utility in agroforestry and traditional medicine. To facilitate its propagation, particularly through in vitro techniques, this study aimed to refine a propagation system by inducing adventitious buds from node explants of mature tree. The study revealed that the Murashige and Skoog (MS) medium, supplemented with 30 g L⁻¹ sucrose and 2.0 mg L⁻¹ thidiazuron (TDZ), effectively stimulated bud break. Furthermore, a combination of 1.0 mg L⁻¹ TDZ and 0.5 mg L⁻¹ α-naphthalene acetic acid (NAA) yielded optimal shoot multiplication, resulting in an average of 16.0 shoots per explant with a length of 5.9 cm. In contrast, utilizing 1.0 mg L⁻¹ 6-benzylaminopurine (BAP) and 0.5 mg L⁻¹ NAA led to producing 10.0 shoots with a height of 3.7 cm. Incorporating TDZ significantly enhanced shoot numbers, size, and overall health of the shootlets. Microscopic analysis revealed that leaves and petioles derived from the TDZ and NAA combination exhibited desirable features, such as a thick cuticle, well-differentiated epidermis, mesophyll, vascular tissues, stomata, and improved vein density compared to those derived from BAP and NAA. The maximum root percentage (87.5%) and adventitious root formation (averaging 8.0 roots with a length of 6.2 cm) were observed on half-strength media supplemented with 1.5 mg L⁻¹ indole-3-butyric acid (IBA). Conversely, NAA fortification resulted in lower rooting percentages (77.8% response with an average of 4.7 roots measuring 4.0 cm in length). Subsequently, the rooted plantlets were successfully acclimatized using a mixture of soilrite®, cocopeat, and garden soil (1:1:1 v/v ratio), with a survival rate of 92.0% in the field. This study contributes valuable insights into the optimized use of growth regulators for the large-scale propagation of P. grandis and related species, ensuring the production of micro-morpho-structurally stable plantlets.

Southern Europe is home to two naturally occurring pear species: the European wild pear (Pyrus pyraster (L.) Burgsd.) and the almond-leaved pear (P. spinosa Forssk.). In addition to these two species, the cultivated pear (P. communis L.) is also grown throughout Europe. Since the cultivated pear is one of the most widespread fruits in Europe, gene flow between the cultivated species and their wild relatives is to be expected. The aim of this study was to determine the genetic diversity of natural populations and whether gene flow from the cultivated pear can alter the genetic composition of wild pear populations. We collected samples from 21 populations of P. pyraster and 22 populations of P. spinosa as well as 24 cultivars of P. communis. DNA fingerprinting based on nine microsatellite markers (SSR) was used to analyze the genetic diversity and structure of the wild pear populations and to assess the relationship between wild and cultivated pears. In general, we found a higher genetic diversity of P. pyraster compared to P. spinosa. In three Mediterranean P. pyraster populations, significant cultivated-to-wild gene flow was observed, whereas in P. spinosa it was rare and only observed in a few individuals. Furthermore, in regions where the ecological niches of the two wild pear species overlap, hybrids between them were also found. This study provides valuable insights into the genetic variability of these species and can significantly advance their use in sustainable forest management, conservation, and breeding programs.

Key message

We have identified poplar clones suitable for dryland forestry, which stand out for their resistance to cavitation, level of anisohydrism, adjustment of cellular water relations and high water use efficiency.

In drylands, such as the arid western region of Argentina, poplar afforestation depends on intermittent furrow irrigation, subjecting the plantations to variable water availability both in time and space. Our objective was to study stem biomass production and drought resistance responses of eight poplar clones, to explore whether there are more suitable varieties for forestry in drylands than those currently cultivated, i.e. the hybrid Populus × canadensis clones ‘Conti’ 12 and ‘Guardi’. We conducted a pot experiment with three levels of water availability (control, moderate stress and severe stress), studying four clones of P. × canadensis, ‘Conti 12’, ‘Guardi’, ‘I-214’ and ‘I45/51’, as well as four clones of the Populus deltoides species, ‘Stoneville 67’, ‘Catfish 2’, ‘Dvina’ and ‘Australiano 129/60’. We found that the clones that were more productive under water stress, ‘I-214’ and ‘I45/51’, were also the most resistant to cavitation. However, these clones were not very productive under high water availability. The ‘Guardi’ and ‘Australiano 129/60’ clones performed best in this situation, showing moderately high productivity under water stress. These clones exhibited the highest degree of anisohydrism, high water use efficiency and ‘Australiano 129/60’ stood out for its low water potential at the point of wilting due to osmotic adjustment. The currently most cultivated variety in Cuyo region, ‘Conti 12’, was less productive, did not make cellular adjustments and had low water use efficiency. These results suggest that other available clones may be more suitable for poplar forestry in drylands and should be evaluated in field trials.