Can the soil geology and chemistry analysis of a site predict the geographic origin of wild edible mushrooms (Porcini group)?


1 of 15Published by Polish Botanical Society

Acta Mycologica

ORIGINAL RESEARCH PAPER

Can the soil geology and chemistry analysis 
of a site predict the geographic origin of 
wild edible mushrooms (Porcini group)?

Elia Ambrosio1*, Pietro Marescotti1, Gian Maria Niccolò Benucci2, 
Grazia Cecchi3, Michele Brancucci4, Mirca Zotti3, Mauro Giorgio 
Mariotti1,5

1 Department of Earth, the Environment and Life Science (DISTAV), University of Genoa, Corso 
Europa 26, 16132 Genoa, Italy
2 Department of Plant, Soil and Microbial Sciences, Michigan State University, 48824 East Lansing, 
MI, USA
3 Laboratory of Mycology, Department of Earth, the Environment and Life Science (DISTAV), 
University of Genoa, Corso Europa 26, 16132 Genoa, Italy
4 GEOSPECTRA S.r.l. Spin off University of Genoa,  Via Palmaria 9/6 L, 16121 Genova, Italy
5 Laboratory of Plant Biology, Department of Earth, the Environment and Life Science (DISTAV), 
University of Genoa, Corso Europa 26, 16132 Genoa, Italy

* Corresponding author. Email: elia.ambrosio.10@gmail.com

Abstract
This study aimed to assess the element content of Porcini mushrooms collected 
from broadleaf Mediterranean forests (NW Italy) and underlying soil layers, and 
to elucidate the chemical connection between the mushrooms and their geographic 
site of origin. Comparing the elements in mushrooms with those in soil samples, 
we observed that the concentration of some microelements detected in mushrooms 
had similar distribution as that measured in both the soil layers assessed, especially 
with surface soil. Statistical analyses showed that the microelement pattern in 
mushrooms reflects the soil site of origin. Moreover, by comparing our results with 
other studies, we observed that the soil where Porcini grow is characterized by a 
high concentration of zinc. Some toxic elements were also detected in mushroom 
samples. Analysis of elements in mushrooms and soil layers can be used for qual-
ity assurance of natural products and help distinguish them from uncertified and 
unknown-origin products.

Keywords
wild edible mushrooms; Boletus edulis group; traceability; soil element content; 
mushroom safety

Introduction

It is well known that mushrooms are able to accumulate diverse chemical elements 
from the environment (e.g., air, water, and soil) or substrates (e.g., wood) where they 
grow [1–4]. Although accumulation capability and the presence of chemical elements 
in sporocarps [5] varies according to nutritional requirements and fungal genotypes, 
several authors have shown that the element content of mushrooms is mainly influ-
enced by the chemical composition of the growing substratum, specifically the soil 
[6,7]. Despite these results, the majority of studies only analyze the presence of heavy 
metals inside a few fungal species from both polluted and unpolluted sites [4–8]. To 
the best of our knowledge, only few studies have analyzed the influence of geology, 
soil-mineralogy, and soil-chemistry on the element content in sporocarps, as well as 
the correlation between chemical elements in mushrooms and in the underlying soil 
layers [9–11].

DOI: 10.5586/am.1130

Publication history
Received: 2019-06-15
Accepted: 2019-08-29
Published: 2019-12-30

Handling editor
Andrzej Szczepkowski, Faculty 
of Forestry, Warsaw University of 
Life Sciences – SGGW, Poland

Authors’ contributions
EA conducted the fieldwork, 
did the species identification, 
analyzed the data, and wrote 
the manuscript; GMNB 
contributed to the statistical 
analysis; PM and MB performed 
the chemical analysis; GC 
and MZ contributed to the 
fieldwork; MGM coordinated 
the PhD project; EA, PM, and 
MZ contributed equally to the 
study plan

Funding
This study was carried out in the 
framework of a PhD project in 
Applied Botany in Agriculture 
and the Environment, University 
of Genoa, Italy. EA was 
supported by MIUR (Ministry 
of Education, Universities 
and Research – Italy) doctoral 
fellowship (2012–2014).

Competing interests
No competing interests have 
been declared.

Copyright notice
© The Author(s) 2019. This is an 
Open Access article distributed 
under the terms of the 
Creative Commons Attribution 
License, which permits 
redistribution, commercial and 
noncommercial, provided that 
the article is properly cited.

Citation
Ambrosio E, Marescotti P, 
Benucci GMN, Cecchi G, 
Brancucci M, Zotti M, et al. 
Can the soil geology and 
chemistry analysis of a site 
predict the geographic origin 
of wild edible mushrooms 
(Porcini group)? Acta Mycol. 
2019;54(2):1130. https://doi.
org/10.5586/am.1130

mailto:elia.ambrosio.10%40gmail.com?subject=Can%20the%20soil%20geology%20and%20chemistry%20analysis%20of%20a%20site%20predict%20the%20geographic%20origin%20of%20wild%20edible%20mushrooms%20%28Porcini%20group%29?
https://doi.org/10.5586/am.1130
http://creativecommons.org/licenses/by/4.0/
http://creativecommons.org/licenses/by/4.0/
https://doi.org/10.5586/am.1130
https://doi.org/10.5586/am.1130


2 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

Wild edible mushrooms are the most valuable nonwood forest products in the 
world [12,13]. Currently, more than 2,000 fungal species are known to produce edible 
sporocarps, which are harvested, consumed, and marketed in more than 85 countries 
[14,15]. Current estimations assign edible mushrooms a global market value that is at 
least $2 billion higher than that of timber products [16–20]. In particular, “Porcini” 
(Boletus edulis s. s., a group that also includes the species B. aereus Bull., B. pinophilus 
Pilát & Dermek, and B. reticulatus Schaeff ) are among the most valuable and widely-
consumed groups of wild mushrooms worldwide. From 20,000 to 100,000 metric tons 
of Porcini are estimated to be consumed annually, at fresh-mushroom prices that varied 
from $60 to $200/kg in 2009 [21,22].

Over the last few decades, consumer demand for specialty and high quality agri-
food products has grown incredibly, and the market is greatly expanding [14–16]. For 
these reasons, the concept of traceability, in terms of detecting the origin and quality 
of products, has become an important criterion in the food sector [23–25]. Despite 
the existence of a legal system [26–28], there is a further need to distinguish between 
high- and low-quality produce and to develop new methods and technologies for 
food traceability. Identifying a product’s geographic site of origin means that we can 
then identify possible risks to human health. Most fraudulent products do not satisfy 
food safety requirements, and they can profoundly damage confidence in typical food 
products.

Molecular analysis of proteins and fatty acid profiles as well as DNA barcoding have 
been widely used to identify the origin of food products [29–33]. Although molecular 
techniques are theoretically informative and precise, they involve high processing costs 
and do not allow us to clearly distinguish product authenticity, i.e., the geographical 
site of origin.

Different chemical and physical approaches, such as gas chromatography, mass 
spectrometry, NIR spectroscopy, and the analysis of trace elements and stable isotopes 
have been developed as alternatives to establish the geographical origin of agri-food 
products [34–38]. Several authors agree that soil elements can be favorably used as 
“signatures” of the geographic provenance of a sample [9,10,24]. For instance, Nik-
karinen and Mertanen [9] analyzed the element content in a Boletus edulis group and 
Lactarius trivialis (Fr.) Fr., growing in two different geological regions in Finland, to 
determine whether geochemical fingerprints can be detected in mushrooms. They 
found that fungal samples differed considerably in trace content based on the geologi-
cal and geographic site of origin. Because soil elements can be used as fingerprints of 
the geographic provenance of an organic sample, we analyzed the chemical content in 
mushrooms and soil layers to detect the origin, quality, and authenticity of the group 
of wild edible mushrooms known as Porcini.

The aims of this study was (i) to investigate the relationships between the element 
content of Porcini mushrooms and the underlying soil layers; (ii) to clarify the chemical 
connection between the mushrooms and their geographic site of origin; (iii) to assess the 
presence of toxic elements in the mushrooms; (iv) to identify possible soil-geochemical 
markers that can be used to trace Porcini mushrooms to their harvesting site; and (v) 
to chemically characterize the soil of selected Porcini sites.

Material and methods

Study area

This study was carried out in two sites, an oak wood and a beech forest, located in 
Liguria (province of Savona) in NW Italy (Fig. 1).

The first site (Site 1), near the province of La Maddalena (44°30'14" N, 8°29'17" E), 
covers an area of approximately 7,500 m2 with an altitude ranging from 340 to 380 m a.s.l. 
The area is dominated by Quercus cerris L., and the site is classified as a high forest.

The second site (Site 2) is located near the province of Vereira (44°27'3" N, 8°32'42" 
E) and covers a total area of approximately 10,000 m2. The altitude is 1,000 m a.s.l. The 
area is dominated by Fagus sylvatica L., and it is classified as a high forest.



3 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

Site 1 lies in a geologically complex area characterized by soils deposited on four dif-
ferent rocks: serpentine schists, calceschists, chlorite-actinolite schists, and conglomerates 
belonging to the Tertiary Piedmont Basin’s stratigraphic succession. In contrast, Site 
2 lies in a geologically homogeneous area characterized by soils deposited exclusively 
on calceschist rock.

The climate is temperate oceanic sub-Mediterranean for both sites [39]. The mean 
annual temperature is 12°C [from 0°C (min) in January to 25°C (max) in July)]. Mean 
annual rainfall is 912 mm [33 mm (min) in July; 122 mm (max) in October] [40].

Sample collection

In spring and fall 2014 and 2015, 20 samples of Boletus reticulatus Schaeff (Fig. 2), were 
collected from the two study sites. The mushroom samples are labeled in Tab. 1, Tab. 6, 

and Tab. 7 and Fig. 5–Fig. 7 with the identifiers 
“M1–M20”. Species identification was carried out 
for both fresh and dried specimens by macro- 
and microscopic observations and a series of 
monographs and keys [41–43]. Nomenclature 
and author abbreviations were used in accordance 
with Hibbett et al. [44], Ima [45], and CBS [46]. 
Two soil samples (1 kg each) were collected be-
neath each mushroom: one soil sample from the 
surface layer (from 0 to 20 cm, labeled SL1–SL20), 
and the other from the deeper layer (from 20 cm 
to 40 cm, labeled DL1–DL20).

To characterize each site from a geochemical 
and mineralogical perspective, we also randomly 
collected 10 soil samples (1 kg each) at each site, 
at a depth between 5 and 20 cm (labeled S1–S20). 
These soil samples were recorded in the center 
of 10 circular plots (4-m radius) selected along 
a transect line as proposed by Feest [47]. All soil 
samples were sieved in situ to remove particles 
>2 cm.

Fig. 1 Geographic location of the study sites.

Fig. 2 Picture of B. reticulatus Schaeff.



4 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

Chemical and physical analysis

The complete sporocarps (cap and stipe) and soil samples were brushed in the field, 
washed with distilled water, and dried at 60°C for 48 hours. They were then powdered, 
sieved and stored in hermetic plastic containers in the laboratory. Elements were detected 
by a field-portable energy dispersive X-ray fluorescence (FP-EDXRF) spectrometer 
(X-MET7500; Oxford Instruments). This is one of the simplest, most accurate, and 
most economic analytical tools to detect the chemical composition of many mineral 
and organic substrates [6,25,48–52]. A total of 5 g of each sample was exposed to X-rays 
and related element concentrations were expressed in ppm.

The pH was measured using the WTW Multiline P3 Set pH meter after equilibrating 
the soil fraction (<2 mm) in deionized water for 12–16 hours. The soil granulometry 
(% of clay, silt, and sand) was classified according to Folk [53].

Statistical analyses

For each mushroom and soil sample, descriptive statistics (min, max, mean, standard 
deviation) were calculated for element concentration, and differences in element content 
were displayed using boxplots.

Pearson’s correlation (r) was used to test the hypothesis of linear independence 
between two variables. This coefficient indicates how well two data sets are intercon-
nected (positively, negatively, or no connection) [54]. In this study, variables were 
represented by element concentration detected in the sporocarps and in both the soil 
portions (surface and deep layers).

A set of multivariate analyses was used to measure the degree of dissimilarity be-
tween mushrooms and soil samples. Specifically, the hierarchical cluster analysis (CA) 
(using the Bray–Curtis dissimilarity index and unweighted pair group method with 
arithmetic mean UPGMA) was performed to discern the geographic site of provenance 
of the samples using their degree of dissimilarity in chemical composition [54].

Principal component analysis (PCA) was used to reduce dimensionality and sum-
marize all variables into a few principal components, which explain the greatest amount 
of variance in the data and can be visualized graphically. PCA was calculated in R using 
FactomineR and factoextra packages [54,55].

Finally, the indicator species analysis (ISA) technique was performed on the element 
concentration matrix in order to identify possible fungal and soil chemical markers 
[54,55].

Before performing statistical analyses, data were normalized using the formula f(x)
x/sum(x).

Data analyses were performed using the R software environment for statistical 
computing and graphics version 3.5.1 [56].

Results

Element content in mushrooms and soil layers

Overall, we analyzed the elements in 80 samples: 20 sporocarps (10 recorded at Site 1 and 
10 at Site 2) and underlying soil samples (20 from the surface layer and 20 from the deep 
soil). In addition, 20 soil samples were taken from a depth between 5 and 20 cm from 
the top of the soil, to perform a general geochemical characterization of the sites.

Chemical element concentrations measured in the B. reticulatus samples are sum-
marized in Tab. 1. Full details on the elements detected in the mushroom samples 
(M1–M20) are provided in Appendix S1. Altogether, we detected the presence of 10 
different elements: Ca, Ti, Mn, Fe, Cr, Ni, Cu, Zn, Sr, and Sb. In some samples, the 
concentration of certain elements (Ti, Fe, Sr) were below or very close to the detection 
limit [43 ppm, 10 ppm, and 1 ppm, respectively (Appendix S1)]. Conversely, high Zn 
concentration was found in most of the analyzed mushroom samples, specifically; 105 
and 311 ppm were the maximum values detected at Site 1 and Site 2, respectively.



5 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

Element concentrations measured in soil samples (SL1–SL20 and DL1–DL20), 
collected beneath each mushroom sample, are summarized in Tab. 2 and Tab. 3, and 
detailed concentration values are listed in Appendix S2 and Appendix S3, respectively. 
Altogether, 26 elements were detected in both the soil layers. In some samples, levels 
of P, Mo, and Sb were below the detection limit, whereas the concentration of other 
elements such as Cr, Co, Ni, Cu, and Zn was very high in both surface and deep soil 
layers (Appendix S2 and Appendix S3).

Specifically, in the surface soil layer the concentration of Cr varied from a minimum 
value of 261 to a maximum of 683 ppm at Site 1, and from 595 to 1,129 ppm at Site 2. 
In contrast, Ni concentration varied from 308 to 554 ppm at Site 1, and from 385 to 
932 ppm at Site 2. The presence of Zn was considerable and it also varied from 89 to 
114 ppm at Site 1, and from 64 to 120 ppm at Site 2.

Similar to the surface layer, we detected a high concentration of Cr, Ni, and Zn in 
the deep soil layer as well. More precisely, in this soil portion, the content of Cr varied 
from 298 to 915 ppm at Site 1, and from 720 to 1,216 ppm at Site 2. The Ni concentra-
tion ranged from 516 to 915 ppm at Site 1, and from 413 to 959 ppm at Site 2. Finally, 
the content of Zn varied from a minimum value of 79 or 96 to a maximum of 115 ppm 
at Sites 1 and 2, respectively.

Soil mineralogy, lithology, and chemistry of the sites

In the soil samples collected at a depth between 5 and 20 cm, we identified the presence 
of 26 elements (Tab. 4), including a high concentration of some microelements (Cr, 
Ni, and Zr) (Appendix S4, S1–S20). More precisely, the highest range of Cr (75–1,871 
ppm), Ni (257–1,371 ppm), and Zr (97–305 ppm) values were detected at Site 1. The 
distribution of macroelements was similar at both the sites.

The geology of Site 1 is different than that of Site 2 (Tab. 5). Site 1 is characterized by a 
high level of geodiversity: the parent rock consists of siliciclastic conglomerate, serpentine 
schist, and calceschist; whereas, the Site 2 is characterized by only calceschist.

The two sites showed variable pH values according to the parent rock (see caption in 
Appendix S4). The lowest pH value corresponds to siliciclastic conglomerate; whereas, 
the highest values were found on calceschist and serpentine schist. More precisely, 
Site 1 soil samples had pH values ranging from 4.27 to 5.83, whereas at Site 2, the pH 
varied from 4.20 to 4.90.

Finally, according to grain size analysis (Tab. 5), the soil texture was classified as 
gravelly sand to muddy gravel for Site 1, and sandy gravel to gravelly mud for Site 2.

Tab. 1 Summary of the element content detected in 20 mushroom samples.

Macroelements (wt %) Microelements (ppm)

Ca Ti Mn Fe Cr Ni Cu Zn Sr Sb

Site 1 Mean 0.128 0.004 0.007 0.022 40 55 48 81 1 60
SD 0.061 0.000 0.008 0.032 9 60 17 18 1 20

Min 0.061 0.004 0.002 0.001 30 5 24 40 1 13
Max 0.269 0.004 0.025 0.095 58 209 73 105 3 84

Site 2 Mean 0.126 0.031 0.006 0.265 45 32 36 152 8 67
SD 0.068 0.040 0.006 0.337 18 24 21 59 11 32

Min 0.057 0.004 0.001 0.001 29 6 20 110 1 13
Max 0.294 0.104 0.017 0.907 90 92 86 311 28 140

Mushroom samples are labeled M1–M20 in Appendix S1.



6 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

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7 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

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8 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

Chemical correlation among mushrooms and soil layers

In order to observe the differences between the element concentration detected in spo-
rocarps and the underlying soil layers, we used a graph based on descriptive statistical 
measurements (see “Material and methods”). Fig. 3 and Fig. 4 display the results of 
the macro- and microelement content detected in mushrooms and soil samples from 
Sites 1 and 2, respectively.

In both sites, the mushroom content differed from the soil samples for some mac-
roelements (Fe, Ca) (Fig. 3). Regarding microelement content, the concentration of 
Zn, Cu, Sr, and Sb did not differ between the mushrooms and the soil layers (Fig. 4). 
Conversely, the content of Cr and Ni was lower in the mushrooms than in the soil 
portions, where we found a high concentration of these elements.

The degree of correlation among the element contents detected in each sample level 
was also calculated by Pearson’s coefficient. Overall, the highest correlation values were 
observed among the soil layers for the majority of the detected elements at both sites. 
For example, a strong positive correlation value (r = 0.91) was obtained for Cr and Zn 
detected in the soil layers in both Sites 1 and 2, respectively (Tab. 6).

The element content measured in the mushrooms, however, did not show strong 
positive correlation values compared to those detected in the underground soil samples. 
The highest positive correlation value in this group (r = 0.57) was observed between the 
Mn content quantified in the mushrooms and in the surface soil layer (Tab. 6).

ns ns ns ns

0.0

0.5

1.0

1.5

2.0

CaO TiO2 MnOFe2O3
Chemical element

pp
m

A
*** * ** **

0.0

2.5

5.0

7.5

10.0

12.5

CaO TiO2 MnOFe2O3
Chemical element

B
ns ns ns ns

0.0

2.5

5.0

7.5

10.0

12.5

CaO TiO2 MnOFe2O3
Chemical element

C

Fig. 3 Boxplot of macroelement content in mushrooms (A), surface soil layer (B), and deep soil 
layer (C) collected at Site 1 (red) and Site 2 (blue). The element concentration is expressed in ppm. 
Statistical significance: **** α = 0.001; *** α = 0.01; ** α = 0.05; * α = 0.1; ns – not significant values.

ns ns ns **** ns ns

0

50

100

150

200

Cr Ni Cu Zn Sr Sb
Chemical element

pp
m

A
**** ** *** ns ns ns

0

400

800

1,200

Cr Ni Cu Zn Sr Sb
Chemical element

B
** ns ** ns * ns

0

400

800

1,200

Cr Ni Cu Zn Sr Sb
Chemical element

C

Fig. 4 Boxplot of microelement content in mushrooms (A), surface soil layer (B), and deep soil layer (C) collected at Site 
1 (red) and Site 2 (blue). Element concentration is expressed in ppm. Statistical significance: **** α = 0.001; *** α = 0.01; ** 
α = 0.05; * α = 0.1; ns – not significant values.



9 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

Multivariate analyses

A set of multivariate analyses was used to measure the degree of dissimilarity among the 
mushroom and soil layer samples. In detail, the result of cluster analysis (Fig. 5, Fig. 6) 
showed that the mushrooms and soil samples do not form clearly distinctive clusters 
based on origin site with regard to macroelements (Fig. 5). Instead, microelement 
concentrations define separate groups based on geographic site of growth (Fig. 6).

The PCA analysis showed that two axes explained 76.1% of the total data variance 
(Fig. 7). Specifically, when considering all the samples together, the different concentra-
tion of some macro- (Ca, Fe, Ti) and microelements (Sb, Zn, Cu, Cr, Ni) separate the 
samples by spatial distribution (M vs. DL and SL).

The ISA results (Tab. 7) emphasize that some elements had a significant indicator 
value (IV). Specifically, we found that some macroelements, such as Fe, Sr, and Mn, 
were significant for mushroom samples, whereas Ca and Ti were significant elements 
for the deep soil layer. For both the surface and deep soil layers, Cr was a common 
significant element.

Discussion

Our results supported the hypothesis that the soil lithology, mineralogy, and chemistry of 
a site can influence the element content in Porcini (here Boletus reticulatus). We showed 
that at both study sites, most elements detected in the sporocarps almost completely 
reflected the content detected in the underlying soil layers (Fig. 3, Fig. 4). In more detail, 
we showed that the concentration of some microelements (Cu, Zn, Sr, Sb) detected in the 
mushrooms is very similar to that measured in both the soil layers (Fig. 4). Conversely, 
some other elements (Cr and Ni) showed a different distribution.

The distribution of macroelements appeared to be variable among the mushrooms 
and the underlying soil samples, especially that of Ca and Fe. We surmised that the 
variation in the macroelement content is due to the wide distribution that these ele-
ments have in soil.

The correlation values obtained (Tab. 5) also emphasized the above-described 
element distribution. The highest correlation values were observed between the soil 
portions, SL and DL (Tab. 5), rather than the same elements compared between either 
soil layer and the mushroom samples. Moreover, the strongest Pearson’s values (0.61 < 
r < 0.91) were obtained by performing the correlation between the element content in 
the surface layer and deep soil, confirming that some microelements have low mobility 
between soil layers.

Tab. 6 Pearson correlation values (r) among the mushroom samples (M) versus the soil layers (surface soil – SL and deep soil – DL).

Samples 
code

Elements

Ca Ti Mn Fe Cr Ni Cu Zn Sr Sb

Total M vs. SL 0.10 0.14 0.40 0.23 0.28 −0.34 −0.03 −0.47 −0.24 0.16
M vs. DL 0.06 −0.55 −0.33 −0.30 0.04 −0.15 0.00 0.07 −0.09 0.36
SL vs. DL 0.48 0.29 0.34 0.29 0.87 0.11 0.73 0.65 0.45 −0.19

Site 1 M vs. SL 0.35 0.00 0.57 −0.58 0.03 −0.30 −0.68 0.03 0.12 0.04
M vs. DL −0.21 0.00 −0.25 −0.47 −0.13 −0.10 −0.28 −0.28 −0.30 0.56
SL vs. DL −0.44 0.79 0.34 0.04 0.91 −0.71 0.68 0.69 −0.24 −0.04

Site 2 M vs. SL −0.11 −0.11 −0.44 −0.08 0.37 −0.39 −0.08 −0.52 −0.51 0.22
M vs. DL 0.18 −0.55 −0.52 −0.60 −0.08 −0.49 −0.24 −0.32 −0.64 0.29
SL vs. DL 0.79 0.50 0.78 0.64 0.68 0.68 0.33 0.91 0.71 −0.28

Positive moderate (0.40 < r < 0.59), strong (0.60 < r < 0.79), and very strong (0.80 < r < 1) correlation values are indicated in bold.



10 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

M
1

M
5 M
3

M
4

M
20 M

7
M

13 M
2

M
14

M
8

M
9

M
6

M
10

M
15

M
19

M
11

M
18

M
12

M
16

M
17

SL
1

SL
11

SL
3

SL
4

SL
5

SL
14

SL
20 DL
11

SL
2

SL
16

SL
17 DL
4

DL
6

DL
10

SL
15

SL
19

SL
13 DL
1

DL
2

DL
5

DL
8

DL
9

DL
16

DL
14

DL
17

DL
15

DL
18

DL
20 SL

18
DL

3
DL

19 DL
7

DL
12

SL
12

DL
13 SL

6
SL

8
SL

9
SL

10 SL
7

0.
0

0.
2

0.
4

0.
6

0.
8

1.
0

He
ig

ht

Site 1
Site 2

M
1

M
2

M
10 M
3

M
6

M
5

M
7 M
8

M
9 M

11
M

16
M

17 M
12

M
13

M
20 M
19

M
15

M
14

M
4 M
18

SL
1

SL
3

SL
2

SL
4

DL
4

DL
1

DL
5 DL

3
DL

2
SL

5
SL

6
DL

13
DL

14
DL

18 SL
8

SL
13 SL
9

SL
14

SL
20 S

L7
SL

10
SL

11
SL

19
SL

18
DL

16
DL

19
SL

15
DL

20
DL

15
DL

17 SL
16

SL
17 DL

6
DL

8
DL

10 DL
7

DL
9 DL
11

SL
12

DL
12

0.
0

0.
2

0.
4

0.
6

He
ig

ht

Site 1
Site 2

−3

0

3

6

−5.0 −2.5 0.0 2.5
Dim1 (63.7%)

D
im

2 
(1

2.
4%

) Sample
DL

M

SL

A

CaO
TiO2

MnO
Fe2O3

Cr
Ni

Cu

Zn
SrSb

−1.0

−0.5

0.0

0.5

1.0

−1.0 −0.5 0.0 0.5 1.0
Dim1 (63.7%)

D
im

2 
(1

2.
4%

)

0.25

0.50

0.75

cos2

B

Fig. 5 Cluster dendrogram of the samples (mushrooms, surface soil layer, and deep soil) based on their macroelement content. Des-
ignations of M1–20, SL1–20, and DL1–20 indicate the mushrooms (M), surface soil layer (SL), and deep soil samples (DL), respectively.

Fig. 6 Cluster dendrogram of the samples (mushrooms, surface soil layer, and deep soil) based on microelement content. Designa-
tions of M1–20, SL1–20, and DL1–20 indicate the mushrooms (M), surface soil layer (SL), and deep soil samples (DL), respectively.

Fig. 7 Graphical representation of principal component analysis. (A) Ordination graph of the first two principal components. 
Ellipses are drawn around the 95% confidence interval for each sample group centroid. (B) Correlation circle between a vari-
able and a principal component (PC). The cos2 value indicates the quality of representation of the variable on the principal 
component. M – mushroom samples; SL – surface soil samples; DL – deep soil samples.



11 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

The degree of chemical dissimilarity among the 
samples is also shown by the cluster analysis (CA) result 
(Fig. 5, Fig. 6). Both dendrograms indicate that mush-
room samples form a distinctive group apart from the 
soil layers. This confirms that our collected mushrooms 
had a different chemical content for some elements (Ca, 
Fe, Ni, and Cr), than that of the soil layers. The analyzed 
mushrooms have accumulated, in fact, a minority of ele-
ments (10 of the 26 analyzed) from the soil. Moreover, 
the CA results also displayed a high degree of similarity 
between the surface and deep soil samples, establishing 
a unique group in the cluster dendrograms.

The result of CA also showed that considering the 
microelement concentration, mushroom samples (M1–
M10 and M11–M20) as well as soil samples established 
distinctive groups on the basis of their geographical sites 
of origin (Fig. 6). This result supported our hypothesis 
that soil geology of origin influences the chemical com-
position of wild edible mushrooms, and suggested that 

some microelements can be used as fingerprints to indicate the geographic provenance 
of a sample.

Additionally, the PCA result confirmed that when considering the whole chemical 
element pattern, the mushrooms samples formed a distinctive group (Fig. 7A) because 
of their higher content of Sb, Zn, and Cu than the soil layers (Fig. 7B).

The chemical analysis performed on our mushrooms and soil samples also revealed 
the presence of some toxic elements in the two sites: Zn, Ni, Cr, Co, and Cu. However, 
it is important to highlight that the high concentrations of some heavy metals (e.g., Cr) 
in the two Ligurian sites is due to natural geological background factors (in this case, 
the presence of serpentine schist parent rocks) of this geographic area, rather than an 
anthropogenic source of pollution. The concentration of these elements is in fact very 
common, and high in soil developed on ophiolitic and ultrabasic rocks [57–59]. The 
presence of toxic elements in mushrooms confirms the mushrooms’ ability to take up 
heavy metals from the growing substratum [1–4,7]. However, it should also be empha-
sized that the content of Cr detected in the sporocarps samples did not exceeded the 
limits of the law, in which tolerable intake values for heavy metals are set by regulatory 
agencies [14,15,60].

Comparing our results with those from different studies is quite difficult, since very 
few studies fully describe the chemical content of wild edible mushrooms, especially 
Porcini, as well as the geology of their sites of growth/origin. Based on the available 
literature, interesting aspects emerge from the comparison of our results with those 
obtained by Nonnis Marzano et al. [10]. These authors analyzed trace element concen-
tration in some Boletus species recorded in Central Italy. Despite a different geology in 
their studied area, concentrations of Zn in both the mushrooms and the soil samples 
were very similar to our results. Also, Giannaccini et al. [61] analyzed the content 
of microelements in the (top)soil and in some edible mushrooms (viz. B. edulis and 
Macrolepiota procera), growing on sedimentary-clastic rocks (prevalently limestone), 
in Central Italy (Tuscany). Specifically, this group found a level of Zn similar to our 
results in both B. edulis and soil samples. Based on these similarities, it may be supposed 
that some specific Italian sites favorable for the growth of Porcini are characterized by 
similar levels of Zn ([Zn] > 100 ppm ca. in the mushrooms and [Zn] < 100 ppm ca. 
in the soil), despite differing in soil geology (for parent rock). In contrast, as variables 
influenced by natural geological background factors, the Cr, Ni, and Sb content detected 
in our sites (and mushroom samples) was higher compared to the other Italian areas 
[7,10,61]. Moreover, in another recent study on the element content of Boletus aereus 
from volcanic areas in South Italy (Sicily), the authors found a high concentration of 
Z, Zn, Cu, Se, and Ti in the analyzed fungal samples [62].

Despite some evidence that emerged from comparing our results with those of 
Nonnis Marzano et al. [10], characterization of the soil chemistry of naturally-growing 
Porcini habitats is quite difficult to perform. Based on these gaps in knowledge, we 
performed statistical analysis (Tab. 7) to detect possible soil and mushroom chemical 

Tab. 7 Summary of the ISA technique.

Element Sample IV p

Ca DL 0.746 0.03*
Ti DL 0.730 0.03*
Fe M 0.997 0.010**
Sr M 0.926 0.020*
Mn M 0.890 0.040*
Cr DL 0.853 0.005**
Cr SL 0.848 0.005**
Ni DL 0.759 0.015*

M, SL, and DL indicate mushrooms, surface soil layer, and deep 
soil samples, respectively. IV – indicator value. Significance: *** 
p = 0; ** p = 0.001; * p = 0.01.



12 of 15© The Author(s) 2019 Published by Polish Botanical Society Acta Mycol 54(2):1130

Ambrosio et al. / Chemical elements in mushrooms and soil layers

indicators. Based on our results, some elements (Ca, Ti, Mn, Sr, and Cr), had a signifi-
cant value, which indicated that they may be considered potential soil and mushroom 
geomarkers.
In conclusion, the results obtained by our study highlight that mushrooms and soil 
samples, with different substrata of origin, differ considerably in their chemical compo-
nents, especially with regard to microelements. This finding leads us to recommend that 
geological and chemical soil information should be included in food traceability.

Based on our results, the application of this method could be the basis for performing 
quality assurance on natural products. The study of chemical content in the mushrooms 
and in the soil layers can protect genuine products and distinguish them from uncerti-
fied and unknown-origin products.

Since the application of geochemical approaches in the mycological field has not been 
widely adopted, future efforts should include more extensive sampling to implement 
this method in protecting human health and food safety.

Acknowledgments

Authors are grateful to G. Nardi for the graphic images, to F. Boccardo for his collaboration in 
the field survey and the picture of Porcini, and to the Managing/Production Editor and T. Hunt 
for linguistic revision. Anonymous reviewers are also acknowledged for useful comments and 
observations.

Supplementary material

The following supplementary material for this article is available at http://pbsociety.org.pl/
journals/index.php/am/rt/suppFiles/am.1130/0:

Appendix S1 Element content detected in the mushroom samples.

Appendix S2 Element content in surface soil layer (0–20 cm) samples (SL1–SL20).

Appendix S3 Element content in deep soil layer (20–40 cm) samples (DL1–DL20).

Appendix S4 Element content in soil layer (5–20 cm) samples (S1–S20).

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	Abstract
	Introduction
	Material and methods
	Study area
	Sample collection
	Chemical and physical analysis
	Statistical analyses

	Results
	Element content in mushrooms and soil layers
	Soil mineralogy, lithology, and chemistry of the sites
	Chemical correlation among mushrooms and soil layers
	Multivariate analyses

	Discussion
	Acknowledgments
	Supplementary material
	References