Trees最新文献

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.

Key message

Climate-growth correlations are non-stationary among all size classes, and large trees are becoming sensitive to August and September drought conditions in the year preceding growth during the last decades.

Abstract

Understanding tree growth and forest dynamics under climate change is paramount to predict changes in carbon cycling, forest development, and ecosystem services. At temperature limited sites, such as alpine treelines, tree growth is often assumed to benefit from rising temperatures, while increased drought may offset potential benefits. Tree size is known to be related to climate sensitivity and drought induced mortality, with large trees generally suffering the most from drought. To assess the relationship of tree size and climate sensitivity for Norway spruce trees at treeline, we collected 158 tree cores at treeline and the adjacent closed canopy forest in the High Tatra Mountains in Slovakia. Size classes were established based on size class isolation of the total sample set, yielding artificial tree ring chronologies with a constant size over time. We ran moving-window correlation analyses to assess the temporal development of climate sensitivity. We found climate-growth correlations to be non-stationary and with similar trends among size classes. In general, trees are temperature limited during the growing season, but correlations have shifted from June to July in recent decades. Additionally, the largest trees show an increased and significant sensitivity to August and September drought conditions in the year preceding growth. These findings emphasize the increasing influence of drought constraints on tree growth, even at supposedly temperature limited treeline sites.

Key message

We identified 7 PtaGRF and 3 PtaGIF genes and analyzed the potential functions of PtaGRF02-PtaGIF02 that may mediate cone development and gibberellin signaling in Chinese pine.

Abstract

Growth-regulating factors (GRFs) and GRF-interacting factors (GIFs) act as transcription cofactors that influence plant growth and development. While these genes have been extensively studied in various plant species, a comprehensive genome-wide analysis of GRFs and GIFs in conifers has been lacking. In this study, we identified 7 PtaGRFs and 3 PtaGIFs in Chinese pine (Pinus tabuliformis) and conducted a detailed analysis of their motifs, domains, structures, and regulatory elements. Phylogenetic analysis revealed that GRF proteins grouped into five clades, with PtaGRFs forming a single clade. We further investigated chromosome mapping and collinearity. Through expression profiling and correlation analysis, PtaGRF02 and PtaGIF02 were excavated, which may play a role in cone development. Protein–protein interaction analysis indicated that these two factors could interact with proteins involved in flower development. Moreover, PtaGRF02 and PtaGIF02 were shown to interact with each other through yeast two-hybrid and BiFC assays, and they were found to interact with PtaDELLAs to modulate gibberellin (GA) signaling. Overall, our findings offer valuable genetic insights into reproductive development in conifers.

Key message

Experimental drought decreased the vitality of ectomycorrhiza and reduced the number of unique morphotypes.

Quercus pubescens (Willd.) is an ectomycorrhizal (ECM) tree species that is capable of withstanding occasional drought events, but the response of its ectomycorrhiza to drought is not well known. An experiment with two rain exclusion plots and two natural precipitation regime plots was established in a secondary sub-Mediterranean oak forest. ECM roots were sampled before the experiment and after 11 months of rain exclusion. ECM root tips were divided into vital and non-vital and quantified. Morphoanatomical characterization and molecular identification were performed for vital ectomycorrhizae to obtain diversity indices and perform community analyses. Soil water content (SWC) in rain exclusion plots was reduced by approx. 6 vol.% relative to natural precipitation regime and was devoid of major peaks in SWC after rain events. After 11 months, ECM vitality and species richness were significantly reduced on rain exclusion plots compared to the natural precipitation regime while ECM community was reduced to a small subset of the most frequent morphotypes, with strongly decreased number of the unique morphotypes. The reduction of unique morphotypes as a result of rain exclusion may compromise the functional diversity of ectomycorrhiza in their role of nutrient uptake, while the reduction of ECM vitality may decrease the absorptive surface for water and nutrients.

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.