Trees最新文献

Key message

Hydraulic properties of wetwood differ from normal sapwood: hydraulic conductivity is null and water contained in wetwood is totally trapped. Wetwood could result from a bad healing of dead branches.

Abstract

Wetwood is a common phenomenon in silver fir (Abies alba Mill.), posing technical challenges for its industrial use. In this study, we thoroughly characterized the properties of this particular wood, investigating the mechanisms governing its formation and exploring its potential physiological relevance for trees. To address these objectives, we used a wide range of techniques, offering a comprehensive insight into the structure of wetwood at different scales, from cellular to whole-tree. Our results revealed significant variability in moisture distribution in the heartwood of the silver fir trees studied, suggesting the absence of a predefined distribution pattern. The physical properties of wetwood differ from those of sapwood, notably in terms of its hydraulic conductivity, which is null. In addition, our study demonstrated that the anatomical characteristics of wetwood are identical to those of normal dry heartwood, including features such as aspirated tori in bordered pits and the absence of nuclei. These results suggest a normal initial duraminization process followed by a progressive resaturation of the heartwood of silver fir. Taken together, these observations strongly suggest that the water present in wetwood is trapped and unavailable for use by the tree, particularly under conditions of prolonged drought.

Plants live in fluctuating environments and daily experience various mechanical stimuli. Wind-induced stem bending leads to local growth modification, but also induces a remote growth response at a distance from the stimulated zone, suggesting long-distance signaling. In a recent study, we revealed the propagation of an electrical response, named 'gradual potential’ (GP), induced by stem bending in poplar (Populus tremula × alba). Although similar in shape to an action potential (AP), the GP shows original characteristics as a decreasing amplitude with the distance and a high propagation speed (until 200 mm s⁻¹) that also decreases. The mechanisms of generation and propagation of the GP remain unknown. As the differences between AP and GP are mainly based on the speed of signal propagation, we focused in this additional study on the method for estimating GP speed. Furthermore, we tested the genericity of this typical bending-induced electrical response by comparing the effect of stem bending between Douglas-fir and poplar using electrophysiological measurements. In-depth analysis on a large number of biological responses confirmed the high-speed characteristics of GP and its exponential decay pattern. Electrical responses analyses on Douglas-fir showed a GP generation after stem bending. However, inter-specific differences in signal amplitude and damping were revealed suggesting a putative role of the stem anatomical structure of these species on the long-range GP generation and propagation.

Key message

Anonlinear mixed effects canopy density model developed withpredictor variables describing stand characteristics and soil nutrientsprovides a high prediction accuracy.

Abstract

Canopy density (CD) of a forest stand is an indicator of describing tree vitality, tree growth, competition status, environmental condition, and climate change. CD is substantially influenced by several site and environmental factors, such as soil, terrain, and stand factors. However, the CD prediction model developed utilizing the important site and environmental factors is still lacking. This study developed a nonlinear mixed-effects (NLME) CD model using data from 259 sample plots distributed across the moso bamboo (Phyllostachys edulis) forests in the eight provinces of southern China. Like fast-growing tree species, moso bamboo has high rates of growth and carbon sequestration, accumulating large amount of biomass in a short period. The CD model includes the effects of factors describing characteristics of terrains, soil and forest stands. The results showed that elevation significantly affected CD. The NLME CD model developed with the significant predictors included are: stand density (N), dominant height (DH), base area (BA), total nitrogen (TN), and soil organic carbon (SOC). When modeling random effects at the provincial level, the fitting accuracy of the model was significantly improved. Among several strategies used in calibrating NLME CD model or estimating random effects, an increased accuracy was obtained with increasing number of sample plots. However, using many sample plots per province to calibrate NLME CD model may increase the inventory costs with a little gain in the accuracy. Using the two medium BA-plots in each province, slope, and elevation or two largest BA-plots at the different slope-aspect could provide a compromise between measurement cost, model use efficiency, and prediction accuracy. NLME CD model can reduce measurement requirements in the field and support forest managers for more effective bamboo forest management strategies.

There is evidence of recent declines in tree growth in the temperate forests of South America, due to the ongoing climate change. This study assessed growth-climate relationships and the xylem hydraulic architecture of coihue (Nothofagus dombeyi (Mirb.) Oerst) trees exposed to the warmer and drier conditions of recent decades. We selected four coihue populations along a latitudinal gradient in the Andes, Chile, corresponding to a wide range of variation in growing season precipitation (northern dry to southern wet sites). Tree-ring width was measured in 24–32 adult trees per site during the last 60 years. We measured wood anatomical traits in a subsample of four trees per site during the last 25 years. All data were correlated with climatic variables. During the studied period, SPEI-6 passed from positive to negative in all sites. Basal area increment decreased by 1.7 mm² year⁻¹ over the period 1960–2020. Tree-ring width had a positive correlation with precipitation at the drier sites and a negative correlation with maximum temperature at the wetter populations. We estimated a density of 1.78 × 10^–4 and 1.2 × 10^–4 vessels µm⁻² in the xylem of dry and wetter sites, respectively. Vessel density had a negative correlation with precipitation at the driest site and a positive correlation with maximum temperature at wetter sites. The hydraulic diameter was smaller under drier conditions, reaching 68–75 µm in the driest and wettest sites, respectively. Among the traits measured, vessel density was the most sensitive to climate. Drier and warmer conditions were associated with an increased number of smaller sized vessels, especially at the northern populations. Compared with the southern populations of our gradient, the northern populations growing at the drier sites are more sensitive to the ongoing changes in climate, and potentially more vulnerable to the even drier conditions projected for the future.

Key message

Radial grain patterns in young E. bosistoana trees are not random but are under genetic control and are correlated to other properties. Detailed high-resolution grain assessments match results from economical larger resolution techniques.

Abstract

Interlocked grain affects stem properties and timber value. Eucalyptus bosistoana is an emerging plantation species that is supported by a breeding programme, and which shows prominent interlocked grain. Grain assessments are difficult, either restricted in their spatial resolution or resource demanding. Comparative analysis of flexible and high-resolution X-ray microtomography grain measurements were shown to match the economical splitting test. Splitting demonstrated that, on average, grain in the 2-year-old E. bosistoana trees was straight close to the pith becoming slightly left-handed over the first 4 mm, but then developing a strong right-handed twist reaching an average of almost 5° by 12 mm. There was, however, a large degree of variability. Further, grain measures obtained from splitting tests correlated to the observed twisting of the stems. Lastly, twisting of timber was under genetic control. The combination of a heritability (h²) value of 0.34 and a coefficient of genetic variation value (r_g) of 44% means that our assessment techniques for young trees could be incorporated into a breeding programme.

Toona sinensis, a precious tree species native to China, faces severe excessive nitrogen (N) stress due to escalating nitrogen deposition. The effects of excessive N (NO₃⁻, NH₄⁺ and NO₃⁻ + NH₄⁺) on root morphology and physiology were investigated in 1-year-old T. sinensis seedlings. Under excessive NH₄⁺, root morphology traits like root surface area and volume were inhibited, and under excessive NO₃⁻, root length, surface area, and volume were more significantly suppressed. However, a minimal decrease in branch number, apical number, specific root area, and specific root length was observed under excessive NO₃⁻ + NH₄⁺. Under excessive NO₃⁻ or NH₄⁺, the activity of N-metabolizing enzymes such as glutamine synthetase (GS), glutamate synthetase (GOGAT), nitrate reductase (NR), and nitrite reductase (NiR) in roots decreased. Under excessive N, the indole acetic acid (IAA) content in roots decreased, while the contents of abscisic acid (ABA) and cytokinins (CTK) increased. Overall, excessive NO₃⁻ or NH₄⁺ induced nutrient overload, which inhibited root development in T. sinensis. On the other hand, hormone signaling was also modulated in response to excess N, and root morphology changed. These findings enhance our understanding of the effects of excessive N stress on T. sinensis and provide guidance for its plantation production.

Key message

Exogenous myo-inositol induces alterations in leaf cell wall structure and energy metabolism disorders, which may contribute to growth inhibition of trifoliate orange seedlings.

Abstract

Myo-inositol (MI) is widely distributed in all living organisms as a central molecule. In plants, de novo biosynthesis of MI is known to function in multiple aspects of plant growth and development. However, the consequences of MI accumulation in regulating plant growth, especially by exogenous supply, have received little attention. In this study, we characterized cell wall structure, target metabolites in energy metabolism, and gene expression changes related to MI metabolism after foliar application of MI to trifoliate orange seedlings. We observed that exogenous MI increases leaf and root MI levels and inhibits plant growth and dry mass accumulation in trifoliate orange seedlings. Additionally, we detected the downregulation of PtrMIPS and upregulation of PtrMIOXs in leaves due to the application of MI. Structural characterization and targeted metabolomics analysis revealed that exogenous MI induces alterations in leaf cell wall structure and energy metabolism disorders, which may contribute to growth inhibition of trifoliate orange seedlings. We propose and discuss a model to explain how exogenous MI exerts a negative impact on trifoliate orange seedling growth.

The majority of taxa with peltate leaves are perennial herbs native to swampy or aquatic habitats or to mesic shaded understorey habitats. These large peltate leaves are formed by a meristematic bridge at the lamina–petiole junction. However, there are also several strong-light exposed, small-leaved, xero- and scleromorphic Myrtaceae with leaf peltation which is formed without a meristem fusion/bridge. Here, abaxial laminar tissue at the insertion point of the petiole forms a basal extension, so that a weak peltation occurs. This shifts the petiole onto the adaxial laminar surface. The formation of micropeltation in Myrtaceae leads to erect leaves that are strongly appressed to the shoot axis and the entire foliate, vertical shoots appear as “green columns”, a result that is also the case in taxa with reflexed minute leaves. It seems that micropeltation achieves the same goal as leaf reflexion in small-leaved taxa—reduction of heat-load and transpiration during the hottest phases of the day by a lower light interception at midday compared to the morning and evening. Thus, physiologically micropeltation and reflexion of minute leaves seem to be the result of convergent evolution.

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.