Are there seasonal variations of trace element concentrations (Cd, Pb, Zn) in wood of Fagus trees in Germany?

A framework for tracing timber following the Ukraine invasion

Scientific testing including stable isotope ratio analysis (SIRA) and trace element analysis (TEA) is critical for establishing plant origin, tackling deforestation and enforcing economic sanctions. Yet methods combining SIRA and TEA into robust models for origin verification and determination are lacking. Here we report a (1) large Eastern European timber reference database (Betula, Fagus, Pinus, Quercus) tailored to sanctioned products following the Ukraine invasion; (2) statistical test to verify samples against a claimed origin; (3) probabilistic model of SIRA, TEA and genus distribution data, using Gaussian processes, to determine timber harvest location. Our verification method rejects 40-60% of simulated false claims, depending on the spatial scale of the claim, and maintains a low probability of rejecting correct origin claims. Our determination method predicts harvest location within 180 to 230 km of true location. Our results showcase the power of combining data types with probabilistic modelling to identify and scrutinize timber harvest location claims.

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.

Seasonal variations in leaf and branch trace elements and the influence of a 3-yr 100% rainfall exclusion on Pinus massoniana Lamb

Background

Trace elements are essential for the growth and survival of plants, and their concentrations and distributions in plants are effective reflections of ecological adaptation strategies. However, this aspect has seldom been addressed.

Method

Changes in the leaf and branch trace elements of Pinus massoniana Lamb, induced by seasonal dynamics and in response to a 3-yr 100% rainfall exclusion, were evaluated.

Results

The results showed that the concentrations of Fe, Cu, Zn, Cd, Ni and Cr in leaves of P. massoniana in the control group had high seasonal resolution. There were three groups according to their patterns over the growing season: (1) nutrient elements (Cu, Zn, Ni and Cd), which continuously decreased in concentration during the growing season, with the highest concentration in spring and the lowest in autumn; (2) accumulating element (Cr), which increased in concentration from spring to autumn; and (3) indifferent element (Fe), which increased in concentration from spring to summer and decreased in concentration from summer to autumn. The concentrations of trace elements in leaves and branches showed no significant differences with mild drought stress, except for Fe and Cr in leaves and Cr in branches, which significantly increased (p < 0.05) under the result of self-selection under mild drought stress. Therefore, the resultant seasonal and drought effects on trace element cycling in P. massoniana could provide theoretical support to respond to future climate change.

Radial patterns of 13 elements in the tree rings of beech trees from Mavrovo National park, FYROM

The radial patterns of 13 elements (N, P, K, Ca, Mg, Fe, Na, Mn, Zn, Cu, Pb, Cd and Co) were analyzed in the tree rings of European beech (Fagus sylvatica L.). The study site was located in an 'unpolluted' beech ecosystem in Mavrovo National Park. Thus, the obtained radial patterns in the beech trees were considered to be physiologically driven without significant pollution influence. The influence of the main climatic factors (temperature and rainfall) was tested. The radial patterns of individual trees were compared in order to find individual responses to environmental impacts. For most of the elements, higher concentrations were recorded in the pith and outer-most rings and lower in the middle part of the wood. The concentration of heavy metals was low, and followed the physiological patterns of other biogenic elements.

Monitoring historical changes in soil and atmospheric trace metal levels by dendrochemical analysis

The use of dendrochemistry for monitoring historical changes in trace metal deposition and mobilisation of metals in soils is evaluated. In experimental studies, mobilisation of trace metals in surface soil following deliberate acidification was recorded in sugar maple (Acer saccharum) tree-rings with minimal lateral movement between rings. Furthermore, positive correlations between wood (3 year section 1993-95) and foliar chemistry (mean concentration 1993-95) were found for Cd and Zn, but not for Cu and Ni, showing that mobility up the tree bole differs between metals. Even so, substantial lateral movement of elements between rings occurs in some species. Stable Pb isotope ratios in tree-rings were used to show that sacred fir (Abies religeosa) is not a useful monitor of Pb deposition because Pb accumulates in the heartwood. Numerous sophisticated analytical techniques are now used in dendrochemical studies, including laser ablation sampling in conjunction with inductively coupled plasma mass spectrometry that enable the multi-element analysis of extremely small tree-rings with low detection limits. Clearly, not all tree species are suitable for dendrochemical studies, but if careful sampling strategies are used and suitable tree species are chosen, the chemical analysis of tree-rings can provide information concerning historical changes in soil and atmospheric trace metal levels unavailable from any other source.