Trees最新文献

Key message

Our results from transcriptomics extend the understanding of the gene expression and major events associated with embryogenesis progression in Taxodium distichum × Taxodium mucronatum.

Abstract

Zygotic embryogenesis is a critical process during seed development in which the plant body plan is established and the meristems responsible for all post-embryonic growth are determined. Taxodium ‘Zhongshanshan’ is a series of superior interspecies hybrids of T. distichum and T. mucronatum and has been widely planted in southeastern China. Understanding the molecular, cellular and metabolic processes of embryonic development will provide important information on the somatic embryogenesis of T. ‘Zhongshanshan’ and further developing zygotic embryogenesis research. In the present study, we sequenced the transcriptomes of zygotic T. distichum × T. mucronatum embryos at several developmental stages, covering most of embryogenesis. Total RNA samples from six zygotic embryo developmental stages were collected for high-throughput RNA sequencing. In total, 46,798 unigenes were identified, and 12,846 differentially expressed genes were annotated. Genes involved in carbohydrate metabolic, such as glycoside hydrolase-, alpha-xylosidase- and xyloglucan endotransglycosylase-encoding genes, were over-represented in early embryogenesis. Genes associated with auxin, gibberellin, and cytokinin signaling pathways and epigenetic genes related to chromatin remodeling, DNA methylation, and histone deacetylase showed significant differential expression during the embryo development process. Moreover, a number of transcription factors related to embryonic development were identified, among which WUSCHEL HOMEOBOX (WOX), NO APCAL MERISTEM (NAM), and LEAFY COTYLEDON1 (LEC1) being more relevant during early and mid-embryogenesis stages. Our results will provide a valuable resource for future studies and will be helpful to the research of T. ‘Zhongshanshan’ breeding programs.

Key message

The machine learning algorithm extreme gradient boosting can be employed to address the issue of long data gaps in individual trees, without the need for additional tree-growth data or climatic variables.

Abstract

The susceptibility of dendrometer devices to technical failures often makes time-series analyses challenging. Resulting data gaps decrease sample size and complicate time-series comparison and integration. Existing methods either focus on bridging smaller gaps, are dependent on data from other trees or rely on climate parameters. In this study, we test eight machine learning (ML) algorithms to fill gaps in dendrometer data of individual trees in urban and non-urban environments. Among these algorithms, extreme gradient boosting (XGB) demonstrates the best skill to bridge artificially created gaps throughout the growing seasons of individual trees. The individual tree models are suited to fill gaps up to 30 consecutive days and perform particularly well at the start and end of the growing season. The method is independent of climate input variables or dendrometer data from neighbouring trees. The varying limitations among existing approaches call for cross-comparison of multiple methods and visual control. Our findings indicate that ML is a valid approach to fill gaps in individual trees, which can be of particular importance in situations of limited inter-tree co-variance, such as in urban environments.

Key message

Oriental beech trees in Hyrcanian forests may exhibit a bimodal growth pattern. While water availability does not limit growth, these trees benefit from warmer weather.

Abstract

Climate projections for the Hyrcanian forests predict higher temperatures and reduced rainfall. However, the impact of these changes on beech tree growth is still debated. This study investigates the intra-annual growth patterns of Oriental beech (Fagus orientalis Lipsky) and their responses to climatic variation within the Hyrcanian forests of northern Iran. We collected micro-cores from six healthy trees in the Sangdeh forest every week from March to September 2022. Microsections were prepared from each core, and the width of the developing tree ring was measured under an optical microscope. We fitted a generalized additive model (GAM) to the measured radial growth increments to model growth and derive daily growth rates. We then used correlations between daily tree growth rates and climatic variables considering different time lags. The results show variable growth patterns within the beech trees, including both unimodal and bimodal growth dynamics during the growing season. Analysis of climatic data indicates a significant positive correlation between temperature and growth rate, particularly with a 15-day lag, while rainfall and humidity exhibit weaker, negative correlations with growth. Surprisingly, sufficient rainfall in the study area may hinder growth due to associated cloud cover, which limits sunshine and photosynthesis. A comparison of variations in radial growth and temperature shows their tight synchronization over the growing season. In conclusion, this study offers insights into the complex interactions between climatic factors and tree growth, with implications for regional forest management and climate change adaptation strategies.

Key message

The deciduous species of the Aronia and Pourthiaea genera are differentiated by the finger-shaped colleters present on the midrib of the adaxial side and the pronounced cuticular folding.

Abstract

This work presents data on taxonomically significant features of leaf micromorphology in six deciduous species from the closely related genera Aronia and Pourthiaea of the subtribe Malinae (formerly Pyrinae, Maloideae) in the family Rosaceae. All species were found to have hypostomate leaves with numerous anomocytic stomata on the abaxial side. However, Aronia arbutifolia, Pourthiaea arguta, and P. villosa showed single stomata on leaf teeth on the adaxial leaf side. All species exhibited stomatal dimorphism, with a large single ‘primary’ stomata at the center of a cluster of smaller ‘secondary’ (ordinary) stomata. Aronia species were characterized by well-defined cuticular striations on the surface of the adaxial epidermis, as well as cuticular radial folds and peristomatic folds in both types of stomata. Cuticular folding in Pourthiaea species is restricted to radial folds in primary stomata and is less pronounced or absent in secondary stomata. All species of Aronia and Pourthiaea have colleters of deltoid or elongated shape in leaf teeth. In A. mitschurinii and A. arbutifolia, rounded colleters were found in the sinuses between the leaf teeth. Aronia species have the unique feature of forming a special type of colleters on the adaxial side of the leaf midribs. In contrast, Pourthiaea species lacked similar structures. The secretion of the colleters showed an intense peak at 670-674 nm with a small shoulder in the range of 695-740 nm in its fluorescence spectrum. The micromorphological features of the studied leaf structures can serve as taxonomic characters in the genera Aronia and Pourthiaea.

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.