Supplementary B - Quality Assurance and Quality Control

1 Plant concentration data

1.1 Step 1: Results of reference materials

Reference materials were randomly incorporated into the routine samples to monitor analytical accuracy, precision, and any potential drift or offsets between batches. This approach also helped identify other types of analytical artifacts.

The reference materials used in this process were UPDEEP_SPRU_BARK_DRY, UPDEEP_SPRU_NEED_DRY, and UPDEEP_SPRU_TWIG_DRY. These materials were developed in-house as reference samples representing the three primary types of materials. While they do not adhere to international reference material standards, they have undergone multiple analyses by external laboratories to establish reliable reference values.

Additionally, the international reference material CLV-2 had been used.

1.1.1 Reference values of the reference materials

Below are the results for the reference values of these three reference materials:

Table 1.1: Table 1.2: Number of above detection limit values for the preanalysed standard reference material (SRM) samples. The SRM samples are described and data is provided by Middleton et al. (2020). These preanalysed SRM analysis were made of dry-milled material with 2F method provided by Actlabs. The values were used as reference values in the x-charts.

Element	UPDEEP_SPRU_BARK_DRY	UPDEEP_SPRU_NEED_DRY	UPDEEP_SPRU_TWIG_DRY
Ag	0	0	0
As	10	10	10
B	10	10	10
Ba	10	10	10
Be	0	0	0
Bi	10	0	1
Ca	10	10	10
Cd	10	10	10
Ce	10	10	10
Co	10	10	10
Cr	10	10	10
Cs	10	10	10
Cu	10	10	10
Dy	10	10	10
Er	10	10	10
Eu	10	10	10
Fe	10	10	10
Ga	10	10	10
Gd	10	10	10
Ge	10	1	9
Hf	8	0	5
Hg	10	0	0
Ho	10	10	10
In	0	0	0
K	10	10	10
La	10	10	10
Li	0	0	0
Lu	0	3	2
Mg	10	10	10
Mn	10	10	10
Mo	10	10	10
Na	10	10	10
Nb	10	10	10
Nd	10	10	10
Ni	10	10	10
Pb	10	7	10
Pd	0	0	0
Pr	10	10	10
Pt	0	0	0
Rb	10	10	10
Re	0	0	0
Sb	10	0	10
Sc	0	0	0
Se	8	4	7
Sm	10	10	10
Sn	1	0	0
Sr	10	10	10
Ta	10	10	10
Tb	10	6	10
Te	5	2	2
Th	10	10	10
Ti	10	10	10
Tl	10	10	10
Tm	0	0	0
U	10	10	10
V	10	10	10
W	1	1	1
Y	10	10	10
Yb	10	10	10
Zn	10	10	10
Zr	10	10	10

1.1.2 Measurement results of the reference materials

The aforementioned reference materials were randomly added to the sample set as supplementary samples within the larger batch of routine samples. Because of their random inclusion, both the sequence and order of the samples varied, as did the total number of measurements taken.

Table 1.3: Number of different SRM samples analysed with the routine samples. The UpDeep reference samples (Norway spruce needles, twigs and bark) are descibed by Middleton et al. (2020) and the CVL-2 (Black spruce) by Dalton and Dunn (1987).

ParentSampleID	N
UPDEEP_SPRU_NEED_DRY	16
UPDEEP_SPRU_BARK_DRY	15
CLV-2	19
UPDEEP_SPRU_TWIG_DRY	16

The results of the measurements of the reference samples provide the following:

Table 1.4: Mean, madian, relative standard deviation (RSD) and relative mean absolute deviation (RMAD) of the four SRMs analysed with the routine samples.

Element	CLV-2_Mean	CLV-2_Median	CLV-2_RSD	CLV-2_RMAD	UPDEEP_SPRU_BARK_DRY_Mean	UPDEEP_SPRU_BARK_DRY_Median	UPDEEP_SPRU_BARK_DRY_RSD	UPDEEP_SPRU_BARK_DRY_RMAD	UPDEEP_SPRU_NEED_DRY_Mean	UPDEEP_SPRU_NEED_DRY_Median	UPDEEP_SPRU_NEED_DRY_RSD	UPDEEP_SPRU_NEED_DRY_RMAD	UPDEEP_SPRU_TWIG_DRY_Mean	UPDEEP_SPRU_TWIG_DRY_Median	UPDEEP_SPRU_TWIG_DRY_RSD	UPDEEP_SPRU_TWIG_DRY_RMAD
Ag	1.7e+01	1.7e+01	20	10	8.8e+00	8.6e+00	13	10	2.6e+00	2.9e+00	46	37	1.1e+01	1.2e+01	14	17
Al	1.1e+02	1.1e+02	13	11	9.3e+01	9.2e+01	6	6	7.6e+01	7.3e+01	15	6	9.4e+01	9.1e+01	14	11
As	3.4e+02	3.4e+02	15	17	3.0e+02	2.9e+02	11	13	1.0e+02	9.7e+01	18	17	5.2e+02	5.2e+02	8	6
Au	8.6e-01	5.2e-01	145	79	1.9e-01	1.5e-01	73	84	2.3e-01	2.5e-01	69	74	9.0e-01	2.1e-01	193	105
B	3.1e+01	4.2e+01	49	47	2.1e+00	1.9e+00	50	5	3.1e+00	2.8e+00	48	12	4.2e+00	2.6e+00	61	8
Ba	2.3e+04	2.3e+04	8	8	1.2e+05	1.2e+05	4	4	4.1e+04	4.1e+04	4	5	6.7e+04	6.6e+04	5	5
Be	4.7e+00	4.2e+00	50	33	1.5e+00	1.6e+00	46	52	4.6e+00	4.4e+00	27	28	1.3e+00	1.4e+00	36	30
Bi	9.8e+00	9.2e+00	21	19	8.9e+00	8.8e+00	16	18	3.3e+00	2.9e+00	77	38	4.1e+00	3.8e+00	52	56
Ca	7.5e+03	7.7e+03	8	5	1.0e+04	1.0e+04	8	10	5.4e+03	5.5e+03	7	7	4.0e+03	4.1e+03	6	4
Cd	1.3e+01	1.3e+01	23	15	1.3e+02	1.3e+02	7	6	1.4e+01	1.4e+01	14	11	4.2e+01	4.2e+01	8	10
Ce	2.3e+02	2.2e+02	10	9	7.6e+01	7.5e+01	10	6	1.7e+01	1.7e+01	8	11	7.7e+01	7.6e+01	12	12
Co	6.7e+01	7.0e+01	13	9	1.3e+02	1.3e+02	8	10	8.2e+01	8.1e+01	8	8	2.4e+02	2.3e+02	11	7
Cr	3.9e+02	3.8e+02	10	7	1.4e+02	1.4e+02	7	8	6.1e+01	4.9e+01	103	18	3.0e+02	3.0e+02	11	12
Cs	1.8e+01	1.7e+01	20	18	3.7e+01	3.7e+01	13	5	7.0e+01	6.9e+01	13	18	8.2e+01	8.2e+01	7	7
Cu	2.0e+03	1.9e+03	13	7	5.1e+03	5.1e+03	2	2	1.4e+03	1.4e+03	5	5	5.9e+03	5.8e+03	4	3
Dy	1.4e+01	1.4e+01	12	11	4.7e+00	4.8e+00	18	24	3.2e+00	3.2e+00	19	15	5.2e+00	5.3e+00	16	11
Er	6.4e+00	6.5e+00	15	17	2.5e+00	2.6e+00	21	23	1.7e+00	1.8e+00	27	13	2.8e+00	2.8e+00	22	22
Eu	4.2e+00	3.6e+00	37	44	1.7e+01	1.8e+01	23	4	6.0e+00	6.3e+00	25	10	8.1e+00	9.6e+00	48	33
Fe	2.6e+02	2.5e+02	9	7	9.2e+01	9.4e+01	6	7	4.0e+01	4.0e+01	6	8	1.2e+02	1.2e+02	4	5
Ga	5.3e+01	3.2e+01	53	37	6.6e+00	6.7e+00	61	75	6.7e+01	6.9e+01	26	14	1.6e+01	1.5e+01	31	16
Gd	1.0e+01	9.8e+00	12	12	5.4e+00	5.1e+00	24	25	2.5e+00	2.3e+00	25	17	5.3e+00	5.1e+00	20	21
Ge	2.8e+00	2.7e+00	41	36	2.9e+00	3.0e+00	29	26	5.3e+00	5.4e+00	30	15	1.3e+01	1.7e+01	64	15
Hf	3.4e+00	2.6e+00	86	31	9.0e-01	8.0e-01	41	45	3.1e-01	2.3e-01	90	68	1.2e+00	1.1e+00	29	24
Hg	2.8e+01	2.9e+01	14	14	1.7e+02	1.7e+02	5	5	2.8e+01	2.8e+01	10	6	2.5e+01	2.5e+01	8	9
Ho	2.6e+00	2.6e+00	8	5	1.1e+00	1.1e+00	19	20	7.9e-01	8.4e-01	22	16	1.0e+00	1.0e+00	19	19
In	4.7e-01	4.2e-01	45	56	3.8e-01	3.4e-01	65	101	1.7e-01	1.4e-01	80	69	2.4e-01	1.9e-01	97	80
K	3.7e+03	3.8e+03	9	4	9.0e+02	8.9e+02	7	7	4.0e+03	3.9e+03	7	8	3.8e+03	3.8e+03	4	2
La	1.2e+02	1.1e+02	12	8	6.4e+01	6.5e+01	8	5	2.3e+01	2.3e+01	7	6	6.4e+01	6.5e+01	7	7
Li	1.8e+02	1.7e+02	20	15	1.0e+01	1.0e+01	27	12	1.9e+01	1.9e+01	13	10	3.3e+01	3.4e+01	13	13
Lu	4.9e-01	4.4e-01	39	43	2.6e-01	1.9e-01	79	44	1.2e-01	1.1e-01	66	62	2.9e-01	1.9e-01	105	37
Mg	8.2e+02	8.6e+02	12	5	2.2e+02	2.3e+02	13	20	8.2e+02	8.2e+02	10	12	9.0e+02	9.0e+02	9	9
Mn	1.7e+06	1.8e+06	9	7	3.8e+05	3.8e+05	4	4	1.1e+06	1.1e+06	3	2	5.4e+05	5.4e+05	4	2
Mo	7.1e+01	7.1e+01	15	14	1.4e+01	1.3e+01	28	19	3.1e+01	3.1e+01	16	11	3.0e+01	2.9e+01	17	8
Na	7.4e+00	7.2e+00	33	38	7.6e+01	7.8e+01	7	8	3.0e+01	3.1e+01	8	8	4.9e+01	5.0e+01	8	4
Nb	9.7e+00	1.2e+01	54	76	3.6e+00	3.2e+00	40	19	8.6e-01	8.4e-01	39	11	6.2e+00	4.0e+00	62	18
Nd	9.7e+01	1.0e+02	13	11	3.7e+01	3.6e+01	12	15	1.4e+01	1.4e+01	16	14	4.4e+01	4.3e+01	16	19
Ni	5.2e+02	5.0e+02	25	11	7.5e+02	7.5e+02	9	8	6.6e+02	6.9e+02	11	9	2.3e+03	2.2e+03	18	3
P	8.8e+02	9.1e+02	9	6	1.8e+02	1.8e+02	10	10	1.4e+03	1.5e+03	8	7	1.1e+03	1.1e+03	7	4
Pb	1.1e+03	1.1e+03	10	7	1.2e+03	1.2e+03	6	7	6.9e+01	6.8e+01	17	9	4.6e+02	4.5e+02	12	7
Pd	2.3e+00	1.5e+00	94	138	6.4e+00	6.6e+00	29	18	4.5e+00	4.8e+00	29	12	3.5e+00	4.4e+00	66	37
Pr	2.5e+01	2.5e+01	12	11	9.8e+00	9.7e+00	11	16	3.6e+00	3.6e+00	10	12	1.1e+01	1.1e+01	16	17
Pt	1.2e-01	3.9e-02	146	136	1.7e-01	2.0e-01	74	99	2.0e-01	1.1e-01	80	116	1.8e-01	1.8e-01	65	75
Rb	2.9e+03	3.0e+03	7	4	4.2e+03	4.2e+03	3	4	1.0e+04	1.0e+04	5	3	1.2e+04	1.2e+04	3	3
Re	2.6e+01	2.6e+01	6	3	4.4e-02	3.5e-02	67	100	3.6e-02	2.1e-02	99	120	3.1e-02	2.3e-02	77	96
Sb	3.9e+01	3.4e+01	39	36	2.6e+01	2.4e+01	37	20	6.5e+00	5.5e+00	67	25	2.9e+01	2.1e+01	59	22
Se	3.5e+02	3.9e+02	50	37	3.7e+01	2.8e+01	99	117	3.3e+01	1.9e+01	100	131	6.1e+01	5.1e+01	86	130
Sm	1.8e+01	1.8e+01	17	9	7.0e+00	7.0e+00	14	13	2.9e+00	2.6e+00	33	36	8.0e+00	8.5e+00	23	16
Sn	7.4e+01	5.1e+01	139	33	1.7e+01	1.6e+01	29	28	4.3e+00	2.9e+00	97	80	1.2e+01	1.3e+01	64	68
Sr	1.7e+04	1.7e+04	8	6	2.7e+04	2.7e+04	3	3	1.9e+04	1.9e+04	3	3	2.1e+04	2.1e+04	6	3
Ta	5.6e-01	4.8e-01	72	69	1.6e+00	1.6e+00	45	51	9.0e-01	4.9e-01	144	101	1.7e+00	1.4e+00	53	23
Tb	2.6e+00	2.6e+00	15	18	1.1e+00	1.0e+00	25	18	5.9e-01	5.8e-01	24	31	1.0e+00	9.8e-01	20	17
Te	1.1e+01	7.6e+00	91	101	8.2e+00	6.0e+00	61	30	5.8e+00	5.9e+00	16	22	4.5e+00	4.8e+00	37	32
Th	4.5e+01	4.4e+01	15	21	6.0e+00	5.7e+00	25	12	1.9e+00	1.5e+00	86	44	6.2e+00	5.8e+00	24	26
Ti	2.3e+03	2.3e+03	19	15	3.1e+03	3.0e+03	12	16	8.9e+02	8.2e+02	23	15	4.1e+03	4.1e+03	15	9
Tl	1.4e+01	1.5e+01	21	22	1.6e+01	1.6e+01	12	6	3.1e+01	3.0e+01	11	6	3.8e+01	3.7e+01	17	16
Tm	6.7e-01	8.0e-01	40	41	1.6e-01	1.6e-01	31	35	1.1e-01	9.7e-02	48	48	2.4e-01	1.8e-01	58	45
U	2.9e+03	3.1e+03	15	11	2.3e+00	2.4e+00	20	17	5.2e-01	4.1e-01	93	56	2.3e+00	2.3e+00	18	25
V	3.0e+02	3.1e+02	9	8	2.4e+02	2.4e+02	4	4	4.8e+01	4.7e+01	18	22	2.3e+02	2.3e+02	6	6
W	1.1e+02	7.8e+01	88	29	4.2e+00	3.6e+00	47	30	9.1e-01	9.0e-01	44	35	4.3e+00	4.2e+00	21	26
Y	6.1e+01	6.3e+01	13	11	3.1e+01	3.0e+01	16	12	3.2e+01	3.1e+01	20	28	3.3e+01	3.3e+01	14	12
Yb	4.9e+00	4.9e+00	18	19	2.1e+00	2.1e+00	28	25	1.2e+00	1.1e+00	41	46	2.2e+00	2.2e+00	34	33
Zn	6.3e+04	6.3e+04	7	3	1.0e+05	1.0e+05	3	3	5.6e+04	5.5e+04	2	2	8.6e+04	8.7e+04	3	3
Zr	8.4e+01	8.0e+01	16	18	3.8e+01	4.0e+01	15	16	7.4e+00	8.1e+00	70	81	4.4e+01	4.4e+01	23	16

1.1.3 Comparison of reference values with measurement values

The preanalysed values are provided from the measurements of the reference material powder at external labs, in this case ACTLAB.

Figure 1.1: X-charts of UPDEEP_SPRY_NEED_DRY/UPDEEP_SPRY_TWIG_DRY/UPDEEP_SPRY_BARK_DRY SRMs analysed with the routine samples (dots) vs. the preanalysed SRM values (mean as solid line, 1st standard deviation as dashed line.) The lines of the predefined values are missing if the SRM values were below detection limit. See Table 1.1 for the numbers of the preanalysed SRMs and their missing values. The two laboratory batches (A20-02249, A20-02250) are distinquised by colour.

Figure 1.2: X-charts of UPDEEP_SPRY_NEED_DRY/UPDEEP_SPRY_TWIG_DRY/UPDEEP_SPRY_BARK_DRY SRMs analysed with the routine samples (dots) vs. the preanalysed SRM values (mean as solid line, 1st standard deviation as dashed line.) The lines of the predefined values are missing if the SRM values were below detection limit. See Table 1.1 for the numbers of the preanalysed SRMs and their missing values. The two laboratory batches (A20-02249, A20-02250) are distinquised by colour.

Figure 1.3: X-charts of UPDEEP_SPRY_NEED_DRY/UPDEEP_SPRY_TWIG_DRY/UPDEEP_SPRY_BARK_DRY SRMs analysed with the routine samples (dots) vs. the preanalysed SRM values (mean as solid line, 1st standard deviation as dashed line.) The lines of the predefined values are missing if the SRM values were below detection limit. See Table 1.1 for the numbers of the preanalysed SRMs and their missing values. The two laboratory batches (A20-02249, A20-02250) are distinquised by colour.

Figure 1.4: X-charts of UPDEEP_SPRY_NEED_DRY/UPDEEP_SPRY_TWIG_DRY/UPDEEP_SPRY_BARK_DRY SRMs analysed with the routine samples (dots) vs. the preanalysed SRM values (mean as solid line, 1st standard deviation as dashed line.) The lines of the predefined values are missing if the SRM values were below detection limit. See Table 1.1 for the numbers of the preanalysed SRMs and their missing values. The two laboratory batches (A20-02249, A20-02250) are distinquised by colour.

The following elements were discarded due to poor precision and repeatability when compared to the reference values: B, Ga, Ge, Nb, Pd, Th, Tm, Zr, Ca, K, P, and Na.

Of these elements, also the main elements Ca, K, P, and Na exhibited poor statistical performance. Despite this, the X-charts for these elements showed a somewhat consistent pattern. This suggests that the issues may stem from factors such as the OES measurement process or potential problems with dry weight measurements, rather than inherent issues with the elements themselves.

Given this, Ca, K, P, and Na were retained in the selection and were not discarded, as their behavior could be attributed to measurement artifacts rather than actual analytical errors.

Thus, only these elements should be discarded due to poor performance in the reference materials: B, Ga, Ge, Nb, Pd, Th, Tm, Zr.

1.2 Step 2: Drift and offset correction

Drift and offset correction was made based on the routine samples, laboratory and field replicate samples.

1.2.1 Before drift correction

Figure 1.5: Raw data concentrations of routine samples, laboratory and field replicates of presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.6: Raw data concentrations of routine samples, laboratory and field replicates of presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.7: Raw data concentrations of routine samples, laboratory and field replicates of presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.8: Raw data concentrations of routine samples, laboratory and field replicates of presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.9: Raw data concentrations of routine samples, laboratory and field replicates of presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.10: Raw data concentrations of routine samples, laboratory and field replicates of presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

1.2.2 After drift correction

Figure 1.11: Drift and offset corrected concentrations of routine samples, laboratory and field replicates presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.12: Drift and offset corrected concentrations of routine samples, laboratory and field replicates presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.13: Drift and offset corrected concentrations of routine samples, laboratory and field replicates presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.14: Drift and offset corrected concentrations of routine samples, laboratory and field replicates presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.15: Drift and offset corrected concentrations of routine samples, laboratory and field replicates presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

Figure 1.16: Drift and offset corrected concentrations of routine samples, laboratory and field replicates presented in the sequence analysed in the laboratory. The two laboratory batches (A20-02249, A20-02250) are presented with colours.

1.3 Step 3: Uncertainty modelling and laboratory precision

Uncertainty modelling was performed using laboratory replicate samples. The relative standard deviation (RSD) was calculated based on existing replicate samples. Then, an uncertainty function was fitted to the RSD and mean replicate value pairs. This model was developed by Hawkins (2014) in A Model for Assay Precision doi link. The laboratory precision for each sample was then calculated based on the fitted function and the sample’s concentration value.

Table of number of lab replicates per tissue.

Table 1.5: Table 1.6: Number of laboratory replicates used for uncertainty modelling and calculation of the laboratory precision.

Tissue	n
Norway spruce bark	5
Norway spruce needle	9
Scots pine bark	5
Common juniper needle	3
Norway spruce twig	7
Common juniper twig	2

Examples for the uncertainty functions:

For each sample and each element, a modelled measurement uncertainty is calculated based on these functions and expressed as RSD. As the concentration levels of various tissue types can differ widely, the uncertainty can also vary significantly between tissue types. Therefore, the elements considered potentially difficult due to high uncertainty are considered separately by tissue type.

Table 1.7: Median of the modelled measurement uncertainty, expressed as relative standard deviation (RSD). Elements with high median RSD (>15%) were excluded from further analysis (show as red in the table).

Tissue	Ag	Al	As	Au	B	Ba	Bi	Ca	Cd	Ce	Co	Cr	Cs	Cu	Dy	Er	Eu	Fe	Ga	Gd	Ge	Hf	Hg	Ho	In	K	La	Li	Lu	Mg	Mn	Mo	Na	Nb	Nd	Ni	P	Pb	Pd	Pr	Pt	Rb	Sb	Se	Sm	Sn	Sr	Ta	Tb	Te	Th	Ti	Tl	Tm	U	V	Y	Yb	Zn	Zr
Common juniper twig	17	8	22	42	7.3	2.2	8.1	1	2.7	4.9	2.5	14	7.2	1.9	11	16	4.8	4	22	12	74	22	4.9	17	31	2.1	8.3	16	420	1.8	1.9	12	3.9	8.7	9.5	3.3	2.1	3.6	8	8.7	21	1.9	39	33	13	110	1.3	5.2	17	49	13	11	9.6	20	20	4.3	13	17	1.9	18
Norway spruce bark	4	8	2.8	49	12	2	4.4	0.88	2.6	4.3	3.4	15	6.5	1.9	9.7	16	3.9	3.8	17	9.6	19	25	3.6	17	19	2.1	8.2	36	440	1.8	1.5	17	3.3	15	9.2	4.9	4.6	3.1	6.6	8.4	47	1.9	17	31	10	59	1.2	4.6	16	48	13	11	3.6	21	14	2.8	13	14	1.4	19
Scots pine bark	15	8	5.6	59	29	3.6	5.3	2.5	2.6	6.5	4.6	16	6.7	1.9	16	17	7.9	4.4	11	17	9.4	32	3.7	17	33	2.1	9.1	52	490	1.8	2.1	15	5.2	22	11	5.8	6.1	3.3	15	13	28	1.9	14	33	19	56	1.5	6.4	21	50	13	11	2.9	26	21	3	13	20	2.1	25
Common juniper needle	38	8	74	63	6.6	2.6	9.3	1.1	3.2	8.7	2.4	16	6.9	1.9	19	18	6	4	76	22	0	34	4.4	18	54	2.1	9.7	39	310	1.8	1.6	7.6	16	16	14	2.9	2	7.9	7.6	17	52	1.9	66	39	29	140	1.3	7.9	28	46	13	11	30	32	42	7.6	13	29	2.2	29
Norway spruce twig	3.8	8	17	32	8.1	2.1	12	2.7	2.9	5	2.9	13	5.6	1.8	11	16	4.2	4	15	12	29	22	4.9	17	51	2.1	8.5	9.5	260	1.8	1.5	13	3	7.3	9.5	3.1	2	3.6	8.9	8.8	43	1.9	42	40	14	96	1.3	6.7	16	49	13	11	2.7	22	20	4.3	13	16	1.5	17
Norway spruce needle	11	8	59	52	7.5	2.3	22	2	6.4	24	3.9	18	5.5	2.1	36	22	6	4.9	41	63	310	73	5.3	25	93	2.1	19	10	720	1.8	1.5	41	8.7	50	32	3.5	2	16	11	54	45	1.9	160	33	68	330	1.4	8.3	62	48	13	14	3	48	100	13	13	47	1.5	58

1.4 Step 4: Field precision

Field precision was assessed using replicate samples collected in the field.

Table 1.8: Table 1.9: Number of field replicate pairs per tissue type

Tissue	V1
Scots pine bark	9
Norway spruce bark	10
Norway spruce twig	10
Common juniper needle	10
Norway spruce needle	10
Common juniper twig	10

For the field replicates, the decision process focuses on the log-ratios of elements because raw concentrations can vary due to mass dilution effects. The variability of these log-ratios across different elements is considered, as it can differ at various locations. The aim is to filter out elements with high variability in their log-ratios across multiple locations.

To do this, we count how many times the relative standard deviation (RSD) of a log-ratio exceeds 20% for each location. The values range from 0 to 10, where 0 means the RSD is always less than 20% for that log-ratio, and 10 means it’s always greater than 20%.

Only elements that passed the measurement uncertainty QAQC test for the specific tissue were used for these log-ratios.

Examples for the log-ratio variability decision triangles:

To determine which elements most frequently contribute to high log-ratio variability in the field, we counted how often each element was involved in log-ratios with high variability. This count was done for both elements in the log-ratio (numerator and denominator), and then the average of these counts was calculated for each element.

1.5 Step 5: Summary of elements

Here is a summary of the elements that were carried forward to the statistical analysis.

Table 1.10: Table 1.11: Element selection across different sample types. Elements which passed all QAQC steps are denoted by ‘+’. ‘MU’, ‘FU’ or ‘SRM’ indicates why the element had been discarded. ‘MU’ stands for Measurement Uncertainty, ‘FU’ denotes Field Uncertainty, and ‘SRM’ refers to Standard Reference Material. Note that FU analysis was only carried out for elements which passed the MU QAQC step.

Element	Common juniper needle	Common juniper twig	Norway spruce bark	Norway spruce needle	Norway spruce twig	Scots pine bark
Ag	MU	MU	FU	FU		MU
Al
As	MU	MU		MU	MU
Au	MU	MU	MU	MU	MU	MU
B	SRM	SRM	SRM	SRM	SRM	MU, SRM
Ba
Bi				MU	FU
Ca
Cd
Ce				MU
Co
Cr	MU		MU	MU		MU
Cs
Cu
Dy	MU			MU		MU
Er	MU	MU	MU	MU	MU	MU
Eu			FU	FU
Fe
Ga	MU, SRM	MU, SRM	MU, SRM	SRM	SRM	SRM
Gd	MU			MU		MU
Ge	SRM	SRM	MU, SRM	SRM	SRM	FU, SRM
Hf	MU	MU	MU	MU	MU	MU
Hg
Ho	MU	MU	MU	MU	MU	MU
In	MU	MU	MU	MU	MU	MU
K
La				MU
Li	MU	MU	MU			MU
Lu	MU	MU	MU	MU	MU	MU
Mg
Mn
Mo			MU	MU		MU
Na	MU
Nb	MU, SRM	SRM	MU, SRM	MU, SRM	FU, SRM	MU, SRM
Nd				MU
Ni
P
Pb				MU
Pd	SRM	SRM	SRM	SRM	SRM	MU, SRM
Pr	MU			MU
Pt	MU	MU	MU	MU	MU	MU
Rb
Sb	MU	MU	MU	MU	MU
Se	MU	MU	MU	MU	MU	MU
Sm	MU			MU		MU
Sn	MU	MU	MU	MU	MU	MU
Sr
Ta	FU		FU	FU
Tb	MU	MU	MU	MU	MU	MU
Te	MU	MU	MU	MU	MU	MU
Th	SRM	FU, SRM	FU, SRM	SRM	FU, SRM	SRM
Ti
Tl	MU	FU	FU	FU	FU	FU
Tm	MU, SRM	MU, SRM	MU, SRM	MU, SRM	MU, SRM	MU, SRM
U	MU	MU		MU	MU	MU
V
Y
Yb	MU	MU		MU	MU	MU
Zn
Zr	MU, SRM	MU, SRM	MU, SRM	MU, SRM	MU, SRM	MU, SRM

2 Environmental variables

2.1 Field precision

The ten field replicates had the following relative standard deviations: