Dendrochemical patterns of calcium, zinc, and potassium related to internal factors detected by energy dispersive X-ray fluorescence (EDXRF)

Clues about wood density and trace-element variability of Schizolobium parahyba var. amazonicum (Huber ex Ducke) Barneby for bioenergy use

The interest of biofuel producers in Neotropical species that have high growth rates, slight wood density variability, and elemental composition that does not compromise the environment has increased in recent decades. We investigated the density and chemical characteristics of wood of Schizolobium parahyba var. amazonicum (Huber × Ducke) Barneby as a source for the generation of bioenergy. Apparent radial wood density profiles (X-ray densitometry (XRD)) and the elemental distribution (X-ray fluorescence (XRF)) of Cl, S, K, and Ca in the wood of nine S. parahyba var. amazonicum trees, divided into three diameter classes (I = 15.5, II = 19.5, and III = 23.5 cm) were analyzed. The high heating value (HHV) of the wood samples was determined, and the energy density was estimated by the product of the HHV and the apparent density. Trees that grew better (classes II and III) produced wood with higher density. These trees showed higher concentrations of K and S, and lower concentrations of Ca and Cl. The highest Cl concentrations were observed in classes with smaller diameters. The chlorine levels met the standards for use of this wood as fuel, but the sulfur levels were higher than the threshold recommended by the ISO 17225-3:2021 guidelines, which can limit the use of the species for certain energy uses. The wood of S. parahyba var. amazonicum had interesting characteristics for the production of bioenergy due to its low density, so it can be used in the production of solid biofuels such as pellets and briquettes. Monitoring chlorine and sulfur is important, since during the combustion of biomass they are released into the atmosphere and can negatively contribute to the effects of climate change.

Clay and soil organic matter drive wood multi-elemental composition of a tropical tree species: Implications for timber tracing

Forensic methods to independently trace timber origin are essential to combat illegal timber trade. Tracing product origin by analysing their multi-element composition has been successfully applied in several commodities, but its potential for timber is not yet known. To evaluate this potential the drivers of wood multi-elemental composition need to be studied. Here we report on the first study relating wood multi-elemental composition of forest trees to soil chemical and physical properties. We studied the reactive soil element pools and the multi-elemental composition in sapwood and heartwood for 37 Azobé (Lophira alata) trees at two forest sites in Cameroon. A total of 46 elements were measured using ICP-MS. We also measured three potential drivers of soil and wood elemental composition: clay content, soil organic matter and pH. We tested associations between soil and wood using multiple regressions and multivariate analyses (Mantel test, db-RDA). Finally, we performed a Random Forest analysis of heartwood elemental composition to check site assignment accuracy. We found elemental compositions of soil, sapwood and heartwood to be significantly associated. Soil clay content and organic matter positively influenced individual element concentrations (for 13 and 9 elements out of 46 respectively) as well as the multi-elemental composition in wood. However, associations between wood and topsoil elemental concentrations were only significant for one element. We found close associations between element concentrations and composition in sapwood and heartwood. Lastly, the Random Forest assignment success was 97.3 %. Our findings indicate that wood elemental composition is associated with that in the topsoil and its variation is related to soil clay and organic matter content. These associations suggests that the multi-elemental composition of wood can yield chemical fingerprints obtained from sites that differ in soil properties. This finding in addition to the high assignment accuracy shows potential of multi-element analysis for tracing wood origin.

The what, how, why, and when of dendrochemistry: (paleo)environmental information from the chemical analysis of tree rings

The chemical analysis of tree rings has attracted the interest of researchers in the past five decades in view of the possibility of exploiting this biological indicator as a widely available, high-resolution environmental archive. Information regarding the surrounding environment can be derived either by directly measuring environmental variables (nutrient availability, presence of pollutants, etc.) or by exploiting proxies (e.g. paleoclimatic and paleoenvironmental reconstructions). This review systematically covers the topic and provides a critical view on the reliability of dendrochemical information. First, we introduce the determinable chemical species, such as major elements, trace metals, isotopic ratios, and organic compounds, together with a brief description of their uptake mechanisms and functions in trees. Subsequently, we present the possibilities offered by analytical techniques in the field of tree ring analysis, focusing on direct methods and recent developments. The latter strongly improved the details of the accessible information, enabling the investigation of complex phenomena associated with plant life and encouraging the direct analysis of new analytes, particularly minor organic compounds. With regard to their applications, dendrochemical proxies have been used to trace several processes, such as environmental contamination, paleoclimate reconstruction, global environmental changes, tree physiology, extreme events, ecological trends, and dendroprovenance. Several case studies are discussed for each proposed application, with special emphasis on the reliability of tracing each process. Starting from the reviewed literature data, the second part of the paper is devoted to the critical assessment of the reliability of tree ring proxies. We provide an overview of the current knowledge, discuss the limitations of the inferences that may be drawn from the dendrochemical data, and provide recommendations for the best practices to be used for their validation. Finally, we present the future perspectives related to the advancements in analytical instrumentation and further extension of application fields.

Testing the applicability of dendrochemistry using X-ray fluorescence to trace environmental contamination at a glassworks site

The potential of dendrochemistry as a tool for tracing anthropogenic contamination at a glassworks site in southeastern Sweden was investigated through a multidisciplinary approach combining continuous high-resolution time series of tree rings and sediment profiles. Tree cores from Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and European aspen (Populus tremula) were analysed for their elemental composition using an energy dispersive X-ray fluorescence (ED-XRF) technique. Sediment cores were sampled along a transect extending from the pollution point source to unpolluted areas and analysed using core-scanning-XRF (CS-XRF). High contaminant concentrations in the soil were found for As (≈2000 ppm), Pb (>5000 ppm), Ba (≈1000 ppm) and Cd (≈150 ppm). The concentrations decreased with depth and distance from the pollution source. The dendrochemical analyses revealed alterations in the Barium, Chlorine and Manganese profiles, allowing the identification of seven potential asynchronous releases from the glassworks. Our results suggest that differences in the response of tree species to elemental uptake together with soil chemical properties dictate the success of dendrochemistry as an environmental monitoring tool.

Do tree rings record changes in soil fertility? Results from a Quercus petraea fertilization trial

Through the variations in their dimension, density, anatomy or isotopes composition, tree rings have provided invaluable proxies to evaluate past changes in the environment. Whereas long-term records of changes in soil fertility are particularly desired for forest ecosystem studies, the use of the chemical composition of tree rings as potential marker is still controversial. Dendrochemistry has sometimes been considered as a promising approach to study past changes in soil chemistry, whereas some authors stated that element translocations in the wood preclude any possibility of reliable retrospective monitoring. Here, we aimed at testing whether the wood elemental content of fertilized oaks (Quercus petraea) differed from control trees >30 years after a NPKCaMg fertilization and, if so, if the date of fertilization could be retrieved from the ring analysis. The contents in N, Mg, P, K, Ca and Mn were measured for each of the 43 sampled trees and in every ring of the 58-year long chronology with a non-destructive method coupling a Wavelength Dispersive Spectroscope (WDS) with a Scanning Electron Microscope (SEM). The results showed significantly higher contents in Ca and lower contents in Mn in fertilized compared to control trees. However, there was no difference in elemental content between the rings of the fertilized trees built in the 20 years before and those built after fertilization. Thus, whereas the effect of fertilization on increasing ring width was dramatic, immediate and relatively short-lasting, the elemental composition of the entire ring sequence was impacted, precluding the dating of the event. These results question the possibility to reconstruct long-term changes in soil fertility based on dendrochemistry.

Space-resolved determination of the mineral nutrient content in tree-rings by X-ray fluorescence

X-ray fluorescence spectroscopy (XRF) offers rapid, multi-elemental, low cost and non-destructive elemental analysis. Different studies have used this technique to investigate distribution and concentration of essential and deleterious elements in vegetation. Special emphasis has been recently placed on the key aspects concerning sampling processes, laboratory protocols and calibration methods for quantitative analysis. The aim of the present study was to develop a quantitative methodology to determine the nutrient content in Pinus taeda tree-rings by XRF. Using a 1 mm X-ray excitation beam from a Rh X-ray tube at 30 kV and 600 μA, and dwell time of 20 s, we present calibration curves for P, S, K, Ca, Mn and Fe based on multi-elemental standard addition using wood matrix of 17-year-old Pinus taeda trees. Satisfactory recoveries of our XRF approach for Ca, P, Mn, S and K (<115%), and tolerable for Fe (123%) were obtained compared to inductively coupled plasma optical emission spectrometry results. The non-destructive and quantitative XRF method allows assessing annual element concentrations of P. taeda trees, in order to provide tools for monitoring the nutrient dynamic in an experimental plantation. Furthermore, a method for elemental quantification based on multi-elemental standard addition using wood matrix is described as a useful procedure for future applications.

Long-term nutrient imbalances linked to drought-triggered forest dieback

Drought-induced forest dieback is causing reductions in productivity, increasing tree mortality and impairing terrestrial carbon uptake worldwide. However, the role played by long-term nutrient imbalances during drought-induced dieback is still unknown. To improve our knowledge on the relationships between dieback and nutrient imbalances, we analysed wood anatomical traits (tree-ring width and wood density), soil properties and long-term chemical information in tree-ring wood (1900-2010) by non-destructive Micro X-ray fluorescence (μXRF) and destructive (ICP-OES) techniques. We studied two major European conifers with ongoing drought-induced dieback in mesic (Abies alba, silver fir) and xeric (Pinus sylvestris, Scots pine) sites. In each site we compared coexisting declining (D) and non-declining (ND) trees. We used dendrochronology and generalized additive and linear mixed models to analyse trends in tree-ring nutrients and their relationships with wood traits. The D trees presented lower growth and higher minimum wood density than ND trees, corresponding to a smaller lumen area of earlywood tracheids and thus a lower theoretical hydraulic conductivity. These differences in growth and wood-anatomy were more marked in silver fir than in Scots pine. Moreover, most of the chemical elements showed higher concentrations in D than in ND trees during the last two-five decades (e.g., Mn, K and Mg), while Ca and Na increased in the sapwood of ND trees. The Mn concentrations, and related ratios (Ca:Mn, Mn:Al and P:Mn) showed the highest differences between D and ND trees for both tree species. These findings suggest that a reduced hydraulic conductivity, consistent with hydraulic impairment, is affecting the use of P in D trees, making them more prone to drought-induced damage. The retrospective quantifications of Mn ratios may be used as early-warning signals of impending dieback.

Evaluation of historical atmospheric pollution in an industrial area by dendrochemical approaches

We conducted a dendrochemical study in order to evaluate the exposure of territories and populations to different types of pollutants and to characterise the history of pollution in one of the most intensely industrialised areas of Europe: the industrial port zone of Fos, also heavily urbanised. To perform the study, two tree species have been selected, Pinus halepensis and Populus nigra, on a rural plot located roughly 20 km away from the industrial harbour, an urban plot located in the city of Fos-sur-Mer and an industrial plot. Our study indicated that poplar was a more relevant model for the dendrochemical studies, exhibiting a higher bioaccumulation capacity than pine except for Hg, Sb and Mn. Moreover, thanks to this work, we observed significant exposure of the trees in the urban and industrial areas to As, Cd, Co, Cu, Mo, Sb, Zn, Al, Ca, and Mg, highlighting the exposure of the territory and populations living in the vicinity of the industrial harbour. The temporal variability of the concentrations measured in the tree rings corresponds to the increasing industrialisation of the territory as well as to the evolution of the industrial processes. Thus, this project highlighted the exposure of the Gulf of Fos to atmospheric emissions (industrial, road and urban) of the industrial harbour as well as the changes over time. It also pointed out the relevance of using dendrochemistry to measure atmospheric exposure of metals and metalloids and its temporal variability.

Towards a better understanding of long-term wood-chemistry variations in old-growth forests: A case study on ancient Pinus uncinata trees from the Pyrenees

Dendrochemical studies in old forests are still underdeveloped. Old trees growing in remote high-elevation areas far from direct human influence constitute a promising biological proxy for the long-term reconstructions of environmental changes using tree-rings. Furthermore, centennial-long chronologies of multi-elemental chemistry at inter- and intra-annual resolution are scarce. Here, we use a novel non-destructive method by applying Micro X-ray fluorescence (μXRF) to wood samples of old Pinus uncinata trees from two Pyrenean high-elevation forests growing on acidic and basic soils. To disentangle ontogenetic (changes in tree age and diameter) from environmental influences (e.g., climate warming) we compared element patterns in sapwood (SW) and heartwood (HW) during the pre-industrial (1700-1849) and industrial (1850-2008) periods. We quantified tree-ring growth, wood density and relative element concentrations at annual (TRW, tree-ring) to seasonal resolution (EW, earlywood; LW, latewood) and related them to climate variables (temperature and precipitation) and volcanic eruptions in the 18th and 19th centuries. We detected differences for most studied elements between SW and HW along the stem and also between EW and LW within rings. Long-term positive and negative trends were observed for Ca and K, respectively. Cl, P and S showed positive trends during the industrial period. However, differences between sites were also notable. Higher values of Mg, Al, Si and the Ca/Mn ratio were observed at the site with acidic soil. Growing-season temperatures were positively related to growth, maximum wood density and to the concentration of most elements. Peaks in S, Fe, Cl, Zn and Ca were linked to major volcanic eruptions (e.g., Tambora in 1815). Our results reveal the potential of long-term wood-chemistry studies based on the μXRF non-destructive technique to reconstruct environmental changes.

Dendrochemical evidence for soil recovery from acidic deposition in forests of the northeastern U.S. with comparisons to the southeastern U.S. and Russia

A soil resampling approach has detected an early stage of recovery in the cation chemistry of spruce forest soil due to reductions in acid deposition. That approach is limited by the lack of soil data and archived soil samples prior to major increases in acid deposition during the latter half of the 20th century. An alternative approach is the dendrochemical analysis of dated wood to detect temporal changes in base cations back into the 19th century. To infer environmental change from dendrochemical patterns of essential base cations, internal factors that affect cation chemistry such as the maturation of sapwood and the spread of wood infection need to be recognized. Potassium concentration was a useful marker of these internal maturation and infection that could affect the concentration of essential base cations in wood. Dendrochemical patterns in samples of red spruce in the eastern United States and Norway spruce in northwestern Russia were used to determine how internal changes in base cations can be separated from external changes in root-zone soil to date major changes in the availability of essential base cations associated with a changing environment.

High-resolution densitometry and elemental analysis of tropical wood

KEY MESSAGE

Understanding the mobility and distribution of chemical elements in wood is necessary to apply dendrochemistry. Crystals are likely stable and could be used to analyze changes in nutrient supply.

ABSTRACT

Dendrochemistry uses the variation in wood chemical composition to infer about past environmental conditions and possible effects on tree growth. Elemental or isotopic variation might also help to identify annual growth where tree rings are anatomically not distinct. However, most elements are-to a certain degree-mobile within wood and may be related to anatomical structures. Therefore, understanding what affects elemental distribution is important to make use of and critically assess the potential of dendrochemistry. We studied the variation of wood density and elements at high spatial resolution in wood of six species with anatomically distinct to rather indistinct tree rings from a Thai monsoon forest. Many elements had a higher concentration in parenchyma than in fiber cells, and the co-variation of elements differed strongly between elements and also between species. Strong wood density changes along the ring boundary were found only in Melia azedarach. In all species, the X-ray images showed crystals. EDX spectra showed that these consist of calcium or silicon (in Chukrasia tabularis) as major elemental components. A high concentration of heavy metals (Fe, Cu and Zn) was found in Vitex peduncularis. We conclude that at least for the species studied the radial variation of elemental concentration is unlikely to reveal annual rings that anatomy could not. However, if elements in crystals are more stable than in cell walls or living protoplasts, analyzing the distribution of elements present in crystals may show environmental conditions that, in turn, influence crystal formation and are little known.