Electronic Supplementary Material

Time resolved sulphur and nutrient distribution in Norway spruce drill cores using ICP-OES

Andrea Ulrich1*, Timothée Barrelet1, 2, 4,Renato Figi2, Heinz Rennenberg3, Urs Krähenbühl4

SA Development of a microwave acid digestion

A good temporal resolution and a reliable quantification of the total sulphur content in Norway spruce 5 or 10 year tree ring segments could be achieved by an acid digestion using 1:1 mixture of nitric acid HNO3 65% and hydrogen peroxide H2O2, 30 % (both Merck suprapurÒ, www.merck.de) in a microwave digestion procedure. Table S1 shows the digestion program finally used.

The influence of MgO on the sulphur recovery rates of doped wood and cellulose standards as well for the standard reference material BCR-CRM 101 (Pine Needles) was studied for MgO amounts of 0, 22.5, 45, 90 and 135 mg/l. The results of the doped wood standards showed no remarkable influence of the MgO on the recovery rate as shown in figure S1

Table S2 presents the averaged results of triple determinations for several biological certified reference materials (NIST 1572 Citrus Leaves, RM 8436 Durum Wheat Flour, NIST 1547 Peach Leaves, BCR 101 Spruce Needles, NIST 1573 Tomato Leaves, RM 8436 Durum Wheat Flour NIST 1515 Apple Leaves and NIST 1575 Pine Needles), decomposed by the final microwave digestion procedure. The data are compared to certified values and concentrations found in the literature [1-10].

SB Signal enhancement by USN

Ultrasonic nebuliser USN was used to improve the signal intensity for low concentrated elements such as sulphur and phosphorous. Figure S2 shows the USN intensity enhancement for the USN compared to a conventional Meinhard nebuliser for sulphur and phosphorous at selected wavelengths. The signal enhancement factor of the USN in comparison to the Meinhard nebuliser was about 7 for sulphur and about 13 for phosphorus.

SC Nutrients in Norway spruce trees

Beside sulphur, other nutrients are of interest, such as macronutrients potassium and calcium, as well as of the micronutrient manganese. The results of the profiles will be discussed with special regard to anthropogenic influences and plant physiological processes.

SC1 Potassium

With respect to the dual function of sulphur as indicator for environmental pollution on one side and as a macronutrient on the other side, also other macronutrients, less affected by external pollution situations are interesting such as potassium or calcium. Potassium shows high element contents in bark of about 2.4 g kg-1 ± 23% in average compared to average wood contents of 0.5 g kg-1 ± 28% (see figure S3) were found for potassium, which confirms literature data [11]. These results are based on four trees from two locations, i.e. two trees at each site, Düdingen (figure S3A) and St Moritz (figure S3B).

Potassium is present in all parts of the tree and known as very mobile. Accordingly, large amounts are found in the radially extending ray cells (i.e. storage and conducting cells) [12]. Chiefly being used in young tissues, it plays important roles for colloid formation, enzyme activation and cell osmosis. The profile in figure S3 shows an upward trend. The highest potassium content was found in the 5 tree rings next to the cambium.

Since potassium is of essential importance for growth and development, it is presumed that the highest concentrations are present in the active cells, i.e. in the sapwood region. Compared to Düdingen trees, where the sapwood-heartwood boundary is found around 1970 (± 6 y), the transition zone in St Moritz trees is found at 1941 (± 16 y). Thus, the potassium content is far less influenced by sapwood-heartwood transition than by the proximity of the cambium. The heartwood/sapwood content ratio (0.9) is three times higher than the values found by Dambrine (1991) (0.33) [13]. However, the difference in the ratio might be caused by influences of location and altitude of the sampling site.

Similarly to sulphur, crown interception enhances the potassium content in the soil underneath spruce trees. Due to dry deposition and wash-out phenomena, element concentration in the precipitation increases during its passage through the crown [14]. Wood from the Düdingen trees contains less potassium (0.26 g kg-1 ± 20%) than wood from St Moritz trees (0.42 g kg-1, ± 29.5%). The fact that the spruce trees from an alpine site have the highest wood potassium content underlines the efficiency of potassium uptake by this species if needed. Mountain environment could explain the increased need for K of the St Moritz trees.

SC2 Calcium

Similarly to sulphur and potassium, the higher calcium contents were found in the bark (10.4 g kg-1, ± 26%) compared to the wood (0.72 g kg-1 ± 11.2%, see figure S4), which was also observed by other authors [15]. Data of four trees from two locations (Düdingen and St Moritz, two trees at each site) were averaged for these results.

Calcium ions are used in cell wall synthesis and also during cell division. They influence the permeability of plant membranes, are used as second messengers for plant responses to signals (both environmental and hormonal) and regulate key enzymes in the cytosol [16]. In a recent study, it has been found that high calcium content in spruce wood and bark lowers the content of heavy metals [17]. This shows that calcium content in forest soils, reflected in wood and bark of trees, can interact with other metals and change their availability.

The uptake of calcium is even more efficient than that of potassium. In the phloem, it is less mobile than potassium and is strongly bond to the xylem vessels [12], due to the numerous hydroxyl groups of lignin [18]. The higher the lignification grade, the higher the calcium content in wood.

Contrasting with the upward trend of potassium content, the wood calcium profiles in figure S4 displays a downward trend, particularly pronounced in the 10 most recent tree rings. As described above, the sapwood-heartwood boundary is found around 1970 for the Düdingen and Frieswil trees, and around 1941 for St Moritz trees. Thus, the declining trend is rather due to the proximity of the cambium than to sapwood-heartwood transition. The declining trend in calcium content of the wood from pith to cambium is likely due to lignification, which is incomplete in the sapwood. Düdingen trees have an average cambial age of 96 years (± 4 y), while for the trees from St Moritz, the average is 156 years (± 19 y). Despite this difference, the profiles from individual, healthy trees without growth irregularities are very similar. The heartwood/sapwood content ratio (1.2) corresponds to literature values (1.17) [13]. Wood from the Düdingen trees contains slightly less calcium (0.71 g kg-1, ± 12.7%) than wood from St Moritz trees (0.79 g kg-1 ± 4.2%).

SC3 Manganese

For manganese higher element content (1.2 g kg-1 ± 39.5%) were found in bark as well, compared to the total content in wood of about 0.18 g kg-1 ± 24.6% in average (see figure S5). These results were obtained by analysis of four trees from two locations (Düdingen and Frieswil, two trees at each site). Manganese ions activate a number of enzymes such as decarboxylases and dehydrogenases [19] in plant cells. They are considered to be moderately mobile in wood [18]. The profiles of manganese in Norway spruce wood (figure S5) are very similar to the calcium profiles (figure S4), but with a steeper downward trend towards cambium. Minimum values are located in the outermost 12 tree rings, where sap transport is particularly efficient.

Düdingen trees contain slightly less manganese (0.17 g kg-1 ± 21.4%) compared to Frieswil trees (0.20 g kg-1 ± 29.7%).

S4 References

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