Effects of an innovative densification process on mechanical and physical properties of beech and Norway spruce veneers

AbstractIncreased wood density is obtained by compressing the wood porous structure under suitable moisture and temperature conditions to improve its physical, mechanical and color properties. A recently proposed wood densification method based on partial removal of lignin and hemicellulose in hot water solution of sodium hydroxide and sodium sulphite has shown promising results on solid wood. However, its applicability and effect on thin wood veneers have not been tested yet. In this study, the timing of the method has been adapted to estimate the densification treatment intensity dependence of wood properties (wood density and modulus of elasticity) and color change of softwood (Norway spruce) and hardwood (beech) veneers. Compared to control, density and rigidity increased, with improved wood properties peaking after only 90 s of treatment intensity. Furthermore, the color became darker after treatment compared to control, with no significant color difference between treatment intensities. In conclusion, densification of veneers, according to the presented adapted method, provides a significant improvement of veneers physical and mechanical properties, and produces color changes perceptible by the human eye. Our results can be further implemented and adapted to application in industrial plants, calling for new application of densified veneers.</jats:p

Axial variation of xylem conduits in giant cacti

Giant columnar cacti store massive amounts of water in their parenchymous storage tissues in order to persist under conditions of extreme aridity. Nevertheless, the relationship between stem water storage capacity and the maximum efficiency to deliver water from the roots to stem storage tissues via xylem vessels remains largely unknown. Indeed, the relationship between the axial water flow in xylem and the lateral flow through the storage tissue may affect the xylem structure and, therefore, the plant water conduction strategies. Since the axial structure of vascular conduits has been demonstrated to be universal (i.e. in a broad spectrum of plant species xylem conduits widen basipetally at the same rate), we wanted to determine if both the vessel size and wall thickness in giant cactae follow the same general rule in spite of the buffer action of water storage tissue. To address these hypotheses, we are investigating anatomical variation in xylem structural traits and storage volume in the stems of giant cacti species belonging to different phylogenetic lineages that are native to both the Northern and Southern hemisphere (e.g.Pachycereus weberi, Echinopsis terschekii, Carnegiea gigantea). We collected cross-sections from 6 to 13 samples along the stem of each plant. We found that vessel lumina increased basipetally following a widening rate similar to what has been documented by the theoretical model (WBE model) and from existing surveys on a wide range of tree species. The conduits double wall thickness (t) and its span (s) ratio decrease basipetally and interplay to reduce the risk of cell collapse. We concluded that the xylem architecture of columnar cacti in this study was not influenced by the buffering action of the surrounding storage tissue, and that axial water transport efficiency is maintained for the length of the path as in many other plant species

Quantitative wood anatomy

Quantitative wood anatomy analyzes the variability of xylem anatomical features in trees, shrubs, and herbaceous species to address research questions related to plant functioning, growth, and environment. Among the more frequently considered anatomical features are lumen dimensions and wall thickness of conducting cells, fibers, and several ray properties. The structural properties of each xylem anatomical feature are mostly fixed once they are formed, and define to a large extent its functionality, including transport and storage of water, nutrients, sugars, and hormones, and providing mechanical support. The anatomical features can often be localized within an annual growth ring, which allows to establish intra-annual past and present structure-function relationships and its sensitivity to environmental variability. However, there are many methodological challenges to handle when aiming at producing (large) data sets of xylem anatomical data. Here we describe the different steps from wood sample collection to xylem anatomical data, provide guidance and identify pitfalls, and present different image-analysis tools for the quantification of anatomical features, in particular conducting cells. We show that each data production step from sample collection in the field, microslide preparation in the lab, image capturing through an optical microscope and image analysis with specific tools can readily introduce measurement errors between 5 and 30% and more, whereby the magnitude usually increases the smaller the anatomical features. Such measurement errors—if not avoided or corrected—may make it impossible to extract meaningful xylem anatomical data in light of the rather small range of variability in many anatomical features as observed, for example, within time series of individual plants. Following a rigid protocol and quality control as proposed in this paper is thus mandatory to use quantitative data of xylem anatomical features as a powerful source for many research topics

Plants in the UK flower a month earlier under recent warming.

Global temperatures are rising at an unprecedented rate, but environmental responses are often difficult to recognize and quantify. Long-term observations of plant phenology, the annually recurring sequence of plant developmental stages, can provide sensitive measures of climate change and important information for ecosystem services. Here, we present 419 354 recordings of the first flowering date from 406 plant species in the UK between 1753 and 2019 CE. Community-wide first flowering advanced by almost one month on average when comparing all observations before and after 1986 (p < 0.0001). The mean first flowering time is 6 days earlier in southern than northern sites, 5 days earlier under urban than rural settings, and 1 day earlier at lower than higher elevations. Compared to trees and shrubs, the largest lifeform-specific phenological shift of 32 days is found in herbs, which are generally characterized by fast turnover rates and potentially high levels of genetic adaptation. Correlated with January-April maximum temperatures at -0.81 from 1952-2019 (p < 0.0001), the observed trends (5.4 days per decade) and extremes (66 days between the earliest and latest annual mean) in the UK's first flowering dataset can affect the functioning and productivity of ecosystems and agriculture

Intra-annual density fluctuations (IADFs) in Pinus nigra (J. F. Arnold) at high-elevation in the central Apennines (Italy)

Abstract: Although wood anatomical features can provide yearly resolved climatic information at sub-seasonal resolution, the occurrence of intra-annual density fluctuations (IADFs) might be triggered by several abiotic factors under different ecological settings. Here, we use information on cambial age and tree-ring width to standardize the frequency of IADFs in European black pines from three different mountain slopes in the central Apennines (Italy). At each site, we sampled isolated 15–30-year pioneer pines above the forest limit, as well as close-grown 40–60-year planted pines at the forest limit. Mainly restricted to the latewood of both pioneer and planted trees, the occurrence of IADFs reveals a significant positive relationship with cambial age and ring width. Although the standardized IADFs are well synchronized between the planted and pioneer pines, the frequency of IADFs in narrow rings was higher in the pioneer pines. Drought conditions in July and August are responsible for the highest IADFs frequency in planted and pioneer pines, respectively. Our study underlines the value of IADFs to obtain a more nuanced understanding of the climatic drivers of wood formation at the intra-annual scale

Author Correction: Limited capacity of tree growth to mitigate the global greenhouse effect under predicted warming.

An amendment to this paper has been published and can be accessed via a link at the top of the paper