Chronologies of earlywood vessels and latewood width disentangle climate drivers of oak growth in a mild oceanic region

We obtained tree-ring chronologies for pedunculate oak along an altitudinal gradient of four sites in NW Iberia, which covers most of the species range within the region. Trees grow under Atlantic climate, with a rainfall maximum in autumn-winter, and a minimum during summer, but lacking a remarkable drought. Chronologies included several earlywood anatomical features and ring widths, which were compared to each other. Latewood width and a subset of six earlywood variables were selected for further analyses, considering the period 1954–2003.The lowest site considerably differed from the rest of the gradient due to its milder conditions. Earlywood and latewood were unrelated at the three upper sites, and both compartments responded to different climatic factors. Hydraulic conductivity determined by vessel size was used to describe tree performance, which was modulated by temperature along the gradient. We hypothesize that the main processes involved are the timing of earlywood formation and carbohydrate dynamics. Water availability during late spring and summer affected latewood width, but only at low elevation.This paper illustrates the complexity of analyzing climate-growth relationships in oceanic areas under the absence of a prevailing limiting factor, while providing a feasible explanation of potential mechanisms involved.     

Growth-ring boundaries of tropical tree species: Aiding delimitation by long histological sections and wood density profiles

Recent methodological advances have opened new perspectives for tropical dendrochonological studies by facilitating the visualization, delimitation, and analyses of tree-rings. One of those improvements was brought by X-ray densitometry, which allows building radial wood density profiles at microscopic scale. Furthermore, recent methods allow for cutting long histological sections to study anatomical variations along the entire radius of trees. These techniques have mainly been applied to low wood-density species from temperate and Mediterranean regions, with only limited applications in the tropics. Here we provide an improved protocol that allows for obtaining long histological sections of tropical woods, apply it to six species with varying wood densities 0.45−0.85 g cm⁻³ (Eucalyptus grandis, Tectona grandis, Acacia mangium, Cedrela fissilis, Hymenaea courbaril, and Copaifera duckei), and explore potential applications for tree-ring analyses. We provide instructions on core-microtome knife adjustments, procedures for softening and sectioning long histological samples of high wood-density species. We also present a multi-proxy approach that combines X-ray density profiles with the histological sections that improve the characterization and distinction of the various and complex tropical growth rings anatomical markers (fibre zone, marginal parenchyma, and ring porosity). This multi-proxy approach also opens the door for obtaining quantitative anatomy and physical parameters of tropical species with (intra-annual resolution. Our proposed approach is thus not only an additional tool to improve ring-boundary delimitation of tropical species, but it also paves the way to more innovative, borderline approaches in tropical dendrochronology.     

Altered growth with blue rings: comparison of radial growth and wood anatomy between trampled and non-trampled Scots pine roots

Our understanding of wood anatomy and radial growth in tree roots remains very incomplete, particularly with respect to how ecological factors affect root growth at a relatively small spatial scale, i.e., within a single root system. Here, we compared root growth with and without trampling exposure on a hiking trail. We conducted a quantitative analysis of radial growth and wood anatomical changes, including compression wood (CW) and blue rings (BRs), of two adjacent Scots pine roots in high resolution. A total of 32 cross sections from two roots sampled every 25 cm at the same distance from the respective stem were compared. The buried root (B) was completely buried and had an unexposed segment on a hiking trail. In contrast, the exposed root (E) had an exposed segment that was trampled. 1706 growth rings were analysed for the common period 1954–2015.We found that the volume of the E root in the trampling zone exceeded ten times the volume of the B root. The root surface area of the exposed sections of the E root was on average 14 times larger than that of the unexposed B root section in the trampling zone. The highest number of missing rings was found in the B root. Root sections sampled at the shortest distance from the stem showed the highest coherence in radial growth pattern, which decreased with increasing distance from the stem.BRs were recognized for the first time in tree roots. In total 25 tree rings contained BRs, and their occurrence was restricted to cross sections of the exposed root. BRs were formed over the course of 25 calendar years, i.e., in 40% of tree rings from the common period 1954–2015. Mean monthly temperatures for the years with and without BRs formation showed that colder November (p = 0. 012) and, albeit only slightly, colder September (p = 0.051) temperatures favoured formation of BRs in Scots pine roots. In addition, mean monthly precipitation in July (p = 0.017) was significantly higher for BR years, suggesting an impact of moisture availability on the formation of BRs in Scots pine roots. The study highlights a high rate of growth discrepancies within a single root system. Further, altered growth of trampled roots with high proportions of BRs opens a new challenge for future dendroecological studies on tree roots.     

Effect of growth rate on mean microfibril angle and cross-sectional shape of tracheids of Norway spruce

The variation of the mean microfibril angle (MFA) and the shape of the cross-section of lumen with the distance from the pith in fast grown Norway spruce were studied by X-ray scattering and optical microscopy. The samples were from stems of a clone of Norway spruce [ Picea abies (L.) Karst.] grown in a fertile site at Nurmijärvi, southern Finland Both the mean MFA and the circularity index of the lumen of the fast-grown trees decreased more gradually as the distance from the pith increased than those in reference trees grown in a medium fertility site. However, in mature wood the mean MFA reached the same level in fast-grown trees as in reference trees (5°–10°) but the cross-sections of the cells remained more circular in fast-grown trees than in reference trees. The dependence of the mean MFA on the distance from the pith was similar for earlywood and latewood, but the values of the mean MFA of latewood were systematically smaller than those of earlywood. Two different X-ray diffraction geometries were compared from the points of view of biology and data analysis.     

Distribution of lead in mycorrhizal and non-mycorrhizal Norway spruce seedlings

Non-mycorrhizal spruce seedlings (Picea abies Karst.) and spruce seedlings colonized with Lactarius rufus (Scop.) Fr. or two strains of Paxillits involutus (Batsch) Fr. were grown in an axenic silica sand culture system with frequently renewed nutrient solution. After successful mycorrhizal colonization, the seedlings were exposed to 1 μM PbCI₂ for 19 weeks. The degree of infection in all of the mycorrhizal treatments approached 100% during the experiment and was not affected by exposure to Pb. However, the number of root tips per root dry weight and the shoot: root ratio, both in the non-mycorrhizal and the mycorrhizal seedlings, had decreased after the 19 week treatment with PbCl₂ Using X-ray microanalysis, the distribution and concentration of Pb in the tissues of mycorrhizal and non-mycorrhizal root tips were compared. In the mycorrhizae of seedlings exposed to Pb no significant accumulation of Pb in the hyphal mantle or in fungal cell walls of the Hartig net were detected. Lead accumulated primarily in the cortex cell walls both of non-mycorrhizal and mycorrhizal root tips. No significant difference of Pb concentrations in root cortex cell walls of non-mycorrhizal and mycorrhizal seedlings was found; except for seedlings colonized with Paxillus involutus strain 537. However, at the endodermis no effect of mycorrhizal fungal colonization on the Pb tissue concentration was detected. The presence of the fungal sheath did not prevent Pb from reaching the root cortex. The endodermis acted as a barrier to Pb radial transport in both mycorrhizal and non-mycorrhizal seedling roots.     

The elemental composition, the microfibril angle distribution and the shape of the cell cross-section in Norway spruce xylem

Relationships between the elemental composition, the microfibril angle (MFA) distribution and the average shape of the cell cross-section of irrigated-fertilised and untreated Norway spruce (Picea abies [L.] Karst.) earlywood were studied. Sample material was obtained from Flakaliden, Sweden. The elemental composition was studied by determining the relative mass fractions of the elements P, S, Cl, K, Ca and Mn by X-ray fluorescence and by determining the mass absorption coefficients for X-rays. X-ray diffraction was used to determine the MFA distribution and the average shape of the cell cross-section. The latter was also determined by light microscopy. In transition from juvenile wood to mature wood, a decrease of the mode of the MFA distribution from 13°–24° to 3°–6° was connected to a change in the shape of the cell cross-section from circular to rectangular. The irrigation-fertilisation treatment caused no change in the MFA distribution or in the shape of the cell cross-section, whereas the mass absorption coefficient was higher and the density was smaller in irrigated-fertilised wood. Larger proportion of the elements S, Cl and K, but smaller proportion of the element Mn, were observed due to the treatment. The results indicate that the shape of the cell cross-section or the MFA distribution are not directly linked to the growth rate of tracheids or to the nutrient-element content in the xylem and only show notable changes as a function of the cambial age.     

Comparison of methods in analysis of the tree spatial distribution pattern

The L-function based on K-function, the pair-correlation function and the uniform angle index used in analyzing the tree spatial distribution pattern were compared on the basis of the data from 5 actual plots and 30 simulated plots. It was concluded that the pair-correlation function and the uniform angle index were more accurate than the L-function; the uniform angle index was more effective and feasible than the L-function and the pair-correlation function; the uniform angle index has an additional advantage that it could combine qualitative and quantitative analyses by using the distribution diagram of the uniform angle index and the average valueW .     

Comparison of methods in analysis of the tree spatial distribution pattern

The L-function based on K-function, the pair-correlation function and the uniform angle index used in analyzing the tree spatial distribution pattern were compared on the basis of the data from 5 actual plots and 30 simulated plots. It was concluded that the pair-correlation function and the uniform angle index were more accurate than the L-function; the uniform angle index was more effective and feasible than the L-function and the pair-correlation function; the uniform angle index has an additional advantage that it could combine qualitative and quantitative analyses by using the distribution diagram of the uniform angle index and the average valueW .     

Studying global change through investigation of the plastic responses of xylem anatomy in tree rings

Variability in xylem anatomy is of interest to plant scientists because of the role water transport plays in plant performance and survival. Insights into plant adjustments to changing environmental conditions have mainly been obtained through structural and functional comparative studies between taxa or within taxa on contrasting sites or along environmental gradients. Yet, a gap exists regarding the study of hydraulic adjustments in response to environmental changes over the lifetimes of plants. In trees, dated tree-ring series are often exploited to reconstruct dynamics in ecological conditions, and recent work in which wood-anatomical variables have been used in dendrochronology has produced promising results. Environmental signals identified in water-conducting cells carry novel information reflecting changes in regional conditions and are mostly related to short, sub-annual intervals. Although the idea of investigating environmental signals through wood anatomical time series goes back to the 1960s, it is only recently that low-cost computerized image-analysis systems have enabled increased scientific output in this field. We believe that the study of tree-ring anatomy is emerging as a promising approach in tree biology and climate change research, particularly if complemented by physiological and ecological studies. This contribution presents the rationale, the potential, and the methodological challenges of this innovative approach.     

Exploring wood anatomy,density and chemistry profiles to understand the tree-ring formation in Amazonian tree species

Long-term analysis of tree growth using annual tree rings is increasingly in demand for tropical tree species. The basis of these studies has traditionally been the anatomical identification of the annual ring boundary. However, the structure of these annual rings has been sparsely explored for complementary physical and chemical wood traits. Here, we explore the relationships among wood density features and chemical elements (S, K, Ca, Mn) involved in the annual tree ring formation of 12 tropical tree species from non-flooded forest in the southern Amazon basin. Transverse wood sections were used for each species to determine: 1) macroscopic distinction (radial growth and wood density), 2) microscopic analyse of vessels, axial and ray parenchyma (anatomy) and 3) X-ray densitometry (physical) and X-ray fluorescence (chemical). For some species, the profiles of wood density, and Ca and Mn content showed intra- and inter-annual patterns that allowed to define and characterize the growth boundary of tree rings. Ca, K and S were mainly distributed in axial parenchyma cells, and around vessels, whereas, Mn was mainly distributed in fibres. Our results showed significant species-specific correlations between tree-ring width, density and concentrations of Ca, K and Mn. The anatomical characterization and the complementary information provided by the density and chemical profiles in some Amazonian species can represent a valuable proxy to improve the definition of annual ring-boundaries and improve the understanding of long-term growth and physiological patterns.     

Comparing methods to analyse anatomical features of tree rings with and without intra-annual density fluctuations (IADFs)

Different methods to analyse variations in vessel size in tree rings with and without intra-annual density fluctuations (IADFs) in Erica arborea L. are presented. These methods are based on the in continuum collection of vessel size data within the ring using digital images. In the analysis of rings from the early-(EW) to late-wood (LW), the following vessel parameters were determined: (a) progressive number, (b) lumen area, and (c) lumen centre of gravity (i.e. distance between lumen centre and EW beginning). To make rings of different width or number of vessels comparable, progressive number and centre of gravity variables were standardised. Different graphical representations and data interpolation techniques were compared. Our results indicate that the most consistent procedure to measure the position and width of IADFs along tree rings should include the following steps: (a) plotting vessel lumen area in relation to standardised progressive number, (b) interpolation of vessel area series using simple moving average, (c) superimposition of curves from series of tree rings with and without IADFs, and (d) the establishment of the points where the two series intercept. Our results show that, in diffuse-porous woods, vessel position can be represented by a simpler automatically detected parameter, thus simplifying the procedure for data collection and analysis. The proposed graphical representation also facilitates the establishment of links between IADFs and ecological processes.     

Relationship between wood anatomy,tree-ring widths and wood density of Pinus sylvestris L. and climate at high latitudes in northern Sweden

In this study, wood anatomy, tree-ring width and wood density of Pinus sylvestris at the northern timberline in Fennoscandia were used to identify relationships among the parameters and to screen them for their climatic signals. Furthermore we investigated the influence of the juvenile wood section for all parameters developed. The measurements of wood anatomy were conducted with confocal laser scanning microscopy (CLSM) while the density profiles were produced using an Itrax MultiScanner. We developed chronologies of ring width, wood density and anatomy for a period between 1940 and 2010. Correlations between wood density and wood anatomy were strong in the latewood part. For some wood anatomy and density chronologies youth trends were found in the juvenile part. Wood density decreased from the pith up to the 9th ring and stabilized afterwards, while cell lumen diameter and lumen area increased simultaneously up to the 15th ring. All chronologies contained strong summer temperature signals. The wood anatomical variables provided additional information about seasonal precipitation which could not be found in wood density and tree-ring widths. Our study confirmed previous results stating that the parameter maximum density contains the strongest climate signal, that is, summer temperatures at the northern timberline. Nevertheless, the intra-annual data on tracheid dimensions showed good potential to supply seasonal climatic information and improve our understanding of climatic effects on tree growth and wood formation.     

Applying methods of hard tissues preparation for wood anatomy: Imaging polished samples embedded in polymethylmethacrylate

Cambial activity records short and long-term environmental signals in xylem anatomy, creating a permanent archive. Quantitative wood anatomy deciphers the relationship between cell structure and function in a spatiotemporal context. Obtaining high-resolution images of wood anatomical preparations is a critical stage in the process of decoding this information. Damage to cellular structures when sectioning by microtome is one of the main problems in the preparation of high-quality micro-sections. Cell damage leads to the occurrence of artifacts – most often related to broken cell walls – hindering the performance of image recognition programs, and increasing the time spent on the manual editing of images. In this work, we propose an alternative method to microtomy, based on embedding-polishing protocols established for hard tissue preparation. Wood samples are embedded in a transparent and non-reactive resin as polymethylmethacrylate (PMM) that is subsequently ground and polished. Being able to acquire images from the stained or unstained polished surfaces of the PMM-blocks and sections (thinner than 100 μm) by using a wide range of optical methods such as reflected polarizing microscopy, epifluorescence microscopy, bright-field microscopy with diffuse illumination and circularly polarizing microscopy. This embedding method improves the mechanical integrity and quality of wood anatomical preparations, eliminating the problem of broken cell walls. Furthermore, this technique allows the preparation and analysis of large tissue surfaces.     

The climate sensitivity of Norway spruce [Picea abies (L.) Karst.] in the southeastern European Alps

To investigate the potential of Norway spruce (Picea abies L. Karst) as a palaeoclimate archive in the southeastern European Alps, tree ring chronologies were developed from trees growing at two sites in Slovenia which differed in their ecological and climatological characteristics. Ring width, maximum latewood density, annual height increment and latewood cellulose carbon isotope composition were determined at both sites and the resulting time-series compared with and verified against instrumental climate data for their common period (AD 1960–AD 2002). Results indicate that ring width sensitivity to summer temperature is very site-dependent, with opposing responses at alpine and lowland sites. Maximum density responds to September temperatures, indicating lignification after cell division has ceased. Stable carbon isotopes have most potential, responding strongly to summer temperature in both alpine and lowland stands. Height increment appears relatively insensitive to climate, and is likely to be dominated by local stand dynamics.     

Detecting invisible growth rings of trees in seasonally dry forests in Thailand: isotopic and wood anatomical approaches

We measured radial variation of carbon isotope composition and vessel traits in tree species in seasonally dry forests of Northeast Thailand to explore a more reliable and amenable method of tropical dendrochronology for trees that lack visually detectable and consistent growth rings. Six Dipterocarpaceae species (3 Shorea, 2 Dipterocarpus, and 1 Hopea species) with indistinct or irregular growth rings and teak (Tectona grandis), a species which forms distinct growth rings, were examined. The δ¹³C value variations in all species showed annual cyclicity. Dipterocarpaceae species usually marked the lowest values of δ¹³C in the middle of the growing season, whereas teak had the lowest values at nearly the end of the growing season. Since the growing season of the species examined almost corresponds to the rainy season in the study area, the δ¹³C variation was likely caused by the change in moisture availability. The different variation pattern of teak was attributable to its stronger dependence on ¹³C-enriched reserved material early in the growing season. Changes in tree vessel traits for all species examined also showed annual cyclicity. Dipterocarpaceae species showed significant correlation between δ¹³C values and vessel measurements. Vessel lumen (mean area, tangential and radial diameter, and proportion of total area) had a negative correlation, whereas vessel frequency showed a positive correlation. The correlations indicated that changes in vessel traits were caused by the seasonal variation of moisture available to the trees. Thus, we concluded that methods using wood anatomy, as well as δ¹³C, have great potential for use as tools in tropical dendrochronology within the context of seasonal climate.     

X-ray microdiffraction reveals the orientation of cellulose microfibrils and the size of cellulose crystallites in single Norway spruce tracheids

The microfibril angle (MFA) distribution and the size of cellulose crystallites in isolated double cell walls of Norway spruce (Picea abies [L.] Karst.) tracheids were determined by synchrotron X-ray microdiffraction using the reflections 200 and 004. Samples were 25 μm thick longitudinal sections of earlywood from annual rings 6–18 of several stems. The asymmetric MFA distributions extended from ?20° to 90°. The mean MFA of tangential cell walls decreased from an average of 24° into 19° from the pith to the bark. The mode of the MFA distribution was about 10° smaller than the mean MFA. The standard deviation of the MFA distribution varied between 18° and 25°. The mean MFA and the mode of the MFA distribution were larger in radial than in tangential cell walls. MFA distributions of mature wood samples exhibited a separate small peak at around 90°. The average width and length of cellulose crystallites varied between 28.9–30.9 Å and 192–284 Å, respectively. Both increased slightly as a function of annual ring number from the pith up to the 15th annual ring. An irrigation–fertilisation treatment of some of the stems resulted in longer cellulose crystallites compared to the untreated stems.     

Comparison of different methods for diversity ordering

Abstract. The measurement of diversity, one of the most important concepts in present-day ecology, can be improved by methods of diversity ordering which have recently been developed. This ordering is achieved by a D(α) diversity index family. Indices of this family show varying sensitivities to the rare and abundant species as the scale parameter, α, changes. The aim of this paper is to review and assess 12 methods of diversity ordering and discuss their relationships in detail. Two of the methods are new to the ecological literature. The diversity ordering methods are compared as to their effectiveness in graphically displaying the differences of community structure and demonstrating the (non-)comparability of communities. Small, medium and large data sets were used to evaluate the methods. A small artificial data set (five to seven species) and a large semi-artificial data set (31 — 141 species) are used in this paper. The results suggest that Rényi's diversity index family and Logarithmic dominance ordering are the most useful methods for diversity ordering of communities of all sizes. Right-tailsum diversity ordering performs well for small communities.     

Measurement methods and variability assessment of the Norway spruce total leaf area: implications for remote sensing

Estimation of total leaf area (LA_T) is important to express biochemical properties in plant ecology and remote sensing studies. A measurement of LA_T is easy in broadleaf species, but it remains challenging in coniferous canopies. We proposed a new geometrical model to estimate Norway spruce LA_T and compared its accuracy with other five published methods. Further, we assessed variability of the total to projected leaf area conversion factor (CF) within a crown and examined its implications for remotely sensed estimates of leaf chlorophyll content (C _ab). We measured morphological and biochemical properties of three most recent needle age classes in three vertical canopy layers of a 30 and 100-year-old spruce stands. Newly introduced geometrical model and the parallelepiped model predicted spruce LA_T with an error <5 % of the average needle LA_T, whereas two models based on an elliptic approximation of a needle shape underestimated LA_T by up to 60 %. The total to projected leaf area conversion factor varied from 2.5 for shaded to 3.9 for sun exposed needles and remained invariant with needle age class and forest stand age. Erroneous estimation of an average crown CF by 0.2 introduced an error of 2–3 μg cm^?2 into the crown averaged C _ab content. In our study, this error represents 10–15 % of observed crown averaged C _ab range (33–53 μg cm^?2). Our results demonstrate the importance of accurate LA_T estimates for validation of remotely sensed estimates of C _ab content in Norway spruce canopies.     

Dynamics of lead accumulation in mycorrhizal and non-mycorrhizal Norway spruce (Picea abies (L.) Karst.)

Twelve-week-old seedlings of Norway spruce (Picea abies (L.) Karst), non-mycorrhizal or mycorrhizal with Laccaria laccata, Paxillus involutus or Pisolithus tinctorius were exposed to 5 M Pb for either 32 or 42 days in a quartz sand-nutrient solution system. Ultrathin sections of mycorrhizal and non-mycorrhizal short roots were examined by X-ray microanalysis. After 42 days Pb treatment, the Pb content of the cortex cell walls was lower in the non-mycorrhizal short roots and in the P. involutus mycorrhizae than in the mycorrhizae of L. laccata or P. tinctorius. The Pb content of the cell walls of the hyphal mantle was higher in P. involutus than in L. laccata or P. tinctorius. The short term experiment over 32 days showed that the Pb content of the cortex cell walls strongly increased during the first 16 days in the non-mycorrhizal roots and the L. laccata mycorrhizae, whereas it increased more slowly in the P. involutus mycorrhizae. After 32 days Pb treatment, the Pb content in the cortex cell walls in the P. involutus mycorrhizae was similar to that in the non-mycorrhizal roots. P. involutus also decreased Pb translocation from the roots to the stems. Mycorrhizal infection was not affected by Pb but with P. involutus, the amount of extramatrical mycelium was reduced by 50% on day 32 compared to day 16. The extramatrical mycelium of L. laccata was not reduced by Pb. It is concluded that ectomycorrhizal fungi differ in their effect on Pb accumulation in the roots of Norway spruce. The binding capacity of the extramatrical mycelium seems to be an important factor.     

Applying climwin to dendrochronology: A breakthrough in the analyses of tree responses to environmental variability

Observational, correlative approaches are one of the backbones of dendrochronology. For instance, climate-growth relationships are usually quantified by calculating Pearson correlations. However, the ability to detect these relationships and the probability of declaring significant correlations by chance pose multiple challenges to such correlative framework. The R climwin package, developed a few years ago within the discipline of animal ecology, overcomes these limitations. In this paper we apply climwin to study relationships between climate and tree-ring widths and anatomy to show the advantages of using this package in the field of dendrochronology. This package allows calculating several models considering multiple windows relating a response variable to the climatic factors at different time resolutions. Then, the most parsimonious model is selected through an information-theoretic approach and randomization tests are computed to establish the significance of the selected model. We compare analyses based on Pearson correlations with climwin results using several environmental drivers (climate variables, drought indices, river flow), response variables (tree-ring width, tracheid lumen area and cell-wall thickness), and tree species from ecologically contrasting sites (cold- and water-limited conifers, Mediterranean riparian ash forests). Analyses of climate-growth/anatomy relationships based on the use of climwin showed several advantages over simple Pearson correlations: (i) they did not depend on the use of arbitrary time intervals of fixed duration, (ii) they allowed reducing probabilities associated with type I and II errors, (iii) they resulted in more consistent findings, (iv) they increased the capacity to detect differences between sites or periods in a time series, and (v) they provided more explanatory power.