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.

Reduced above-ground growth and wood density but increased wood chemical concentrations of Scots pine on relict charcoal hearths

Deciphering the drivers of tree growth is a central aim of dendroecology. In this context, soil conditions may play a crucial role, since they determine the availability of water and nutrients for trees. Yet, effects of systematically differing soil conditions on tree growth render a marginally studied topic. In this context, relict charcoal hearths (RCH) - a widespread legacy of anthropogenic charcoal production - render a valuable 'natural' experiment to study possible effects of artificially altered soil conditions on tree growth. We hypothesize, that the differing physico-chemical properties of RCH result in differing wood properties if compared to trees growing on unmodified soils. To test this hypothesis, we analyzed tree-growth, wood density, and wood elemental concentrations of Scots pine as well as physico-chemical soil properties. We applied a classic control-treatment design to compare RCH with unmodified soils. Our analyses identified significantly lower above-ground wood production but systematically higher wood elemental concentrations in RCH-trees compared to control trees. Since we could not identify treatment-specific growth patterns, we hypothesize the observed lower above-ground productivity of Scots pine to indicate an increased root-shoot ratio to compensate for a potentially lower plant water availability on RCH-sites. The observed higher wood elemental concentrations likely reflect higher soil elemental concentrations of Fe, Ca, K, and Mn in RCH soils. In conclusion, our study highlights diverse effects of RCH on tree growth and wood properties and strengthens the value of dendro-chemistry to use the tree-ring archive as proxy for soil conditions within a dendro-ecological context.

A multi-omics approach reveals function of Secretory Carrier-Associated Membrane Proteins in wood formation of​ ​​Populus​​ ​trees

Background

Secretory Carrier-Associated Membrane Proteins (SCAMPs) are highly conserved 32–38 kDa proteins that are involved in membrane trafficking. A systems approach was taken to elucidate function of SCAMPs in wood formation of Populus trees. Phenotypic and multi-omics analyses were performed in woody tissues of transgenic Populus trees carrying an RNAi construct for Populus tremula x tremuloides SCAMP3 (PttSCAMP3; Potri.019G104000).

Results

The woody tissues of the transgenic trees displayed increased amounts of both polysaccharides and lignin oligomers, indicating increased deposition of both the carbohydrate and lignin components of the secondary cell walls. This coincided with a tendency towards increased wood density as well as significantly increased thickness of the suberized cork in the transgenic lines. Multivariate OnPLS (orthogonal projections to latent structures) modeling of five different omics datasets (the transcriptome, proteome, GC-MS metabolome, LC-MS metabolome and pyrolysis-GC/MS metabolome) collected from the secondary xylem tissues of the stem revealed systemic variation in the different variables in the transgenic lines, including changes that correlated with the changes in the secondary cell wall composition. The OnPLS model also identified a rather large number of proteins that were more abundant in the transgenic lines than in the wild type. Several of these were related to secretion and/or endocytosis as well as both primary and secondary cell wall biosynthesis.

Conclusions

Populus SCAMP proteins were shown to influence accumulation of secondary cell wall components, including polysaccharides and phenolic compounds, in the woody tissues of Populus tree stems. Our multi-omics analyses combined with the OnPLS modelling suggest that this function is mediated by changes in membrane trafficking to fine-tune the abundance of cell wall precursors and/or proteins involved in cell wall biosynthesis and transport. The data provides a multi-level source of information for future studies on the function of the SCAMP proteins in plant stem tissues.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4411-1) contains supplementary material, which is available to authorized users.

Common trends in elements? Within- and between-tree variations of wood-chemistry measured by X-ray fluorescence - A dendrochemical study

Element composition of annually resolved tree-rings constitutes a promising biological proxy for reconstructions of environmental conditions and pollution history. However, several methodological and physiological issues have to be addressed before sound conclusions can be drawn from dendrochemical time series. For example, radial and vertical translocation processes of elements in the wood might blur or obscure any dendrochemical signal. In this study, we tested the degree of synchronism of elemental time series within and between trees of one coniferous (Pinus sylvestris L.) and one broadleaf (Castanea sativa Mill.) species growing in conventionally managed forests without direct pollution sources in their surroundings. Micro X-ray fluorescence (μXRF) analysis was used to establish time series of relative concentrations of multiple elements (Mg, Al, P, Cl, K, Ca, Cr, Mn, Fe and Ni) for different stem heights and stem exposures. We found a common long-term (decadal) trend for most elements in both species, but only little coherence in the high frequency domain (inter-annual variations). Aligning the element curves by cambial age instead of year of ring formation reduced the standard deviations between the single measurements. This points at an influence of age on longer term trends and would require a detrending in order to extract any environmental signal from dendrochemical time series. The common signal was stronger for pine than for chestnut. In pine, many elements show a concentration gradient with higher values towards the tree crown. Mobility of elements in the stem leading to high within- and between-tree variability, as well as a potential age-trend apparently complicate the establishment of reliable dendrochemical chronologies. For future wood-chemical studies, we recommend to work with element ratios instead of single element time series, to consider potential age trends and to analyze more than one sample per tree to account for internal variability.