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b i om a s s an d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 4 1 0e1 4 1 8
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Biomass productivity and phytoremediation potentialof Salix alba and Salix viminalis
Miros1aw Mleczek a, Pawe1 Rutkowski b,*, Iwona Rissmann a, Zygmunt Kaczmarek c,Piotr Golinski a, Kinga Szentner a, Katarzyna Stra _zy�nska b, Agnieszka Stachowiak b
aUniversity of Life Sciences in Poznan, Department of Chemistry, Wojska Polskiego 75, 60-625 Poznan, PolandbUniversity of Life Sciences in Poznan, Department of Silviculture, Wojska Polskiego 69, 60-625 Poznan, Polandc Institute of Plant Genetics, Polish Academy of Sciences, Strzeszynska 34, 60-479 Poznan, Poland
a r t i c l e i n f o
Article history:
Received 20 May 2009
Received in revised form
17 March 2010
Accepted 16 April 2010
Available online 11 May 2010
Keywords:
Accumulation
Biomass
Heavy metals
Salix clone
Soil
Abbreviations and definitions: BAF, bioaccumhigh level of a metal to a specified concPAH, polycyclic aromatic hydrocarbons; PCrender harmless toxic compounds contamin* Corresponding author. Tel.: þ48 608295052.E-mail address: [email protected] (
0961-9534/$ e see front matter ª 2010 Elsevdoi:10.1016/j.biombioe.2010.04.012
a b s t r a c t
The aim of this work was to determine selected Salix clones’ capacities for biomass
production and accumulation of heavy metal ions. Determination of the relationship
between sorption of metals and biomass productivity was a further purpose of this study.
Eight Salix viminalis cultivars and one Salix alba cultivar were analyzed. The taxa charac-
terized by greatest biomass production were S. alba var. Chermesina and S. viminalis ‘1056’
(respectively 6.8 and 4.3 kg of fresh mass per shrub per year).
The results have revealed significant differences among clones. The clones most
effective in accumulating all five metals were S. viminalis ‘1154’ and ‘1054’. The studied Salix
population was significantly diverse as regards accumulation efficiency. The differences
between the highest and lowest heavy metal content in extreme clones were for: Cd 84%,
Cu 90%, Hg 167%, Pb 190% and Zn 36%. At the same time, significant differences were
observed in Salix structure. The greatest cellulose content was observed in S. viminalis
‘Sprint’ (49.69%) and the lowest in S. viminalis ‘1059’ (42.09%).
ª 2010 Elsevier Ltd. All rights reserved.
1. Introduction energy option for the future, its implementation in Europe at
Energy production from biomass currently has a high political
priority, as for example shown by the European Union target
of a 20% share of renewable energy by 2020 [1]. It can be
expected that the cultivation of short rotation coppice (SRC)
and perennial energy grasses (PEG) for heat and power
generation will become more important after 2010 when new
technologies enter the market and bio-heat options are
further developed. Nevertheless, even if the cultivation of PEG
and SRC is often considered as a very promising renewable
ulation factor; Hyperacentration or to a specifiB, polychlorinated bipheating the environment; T
P. Rutkowski).ier Ltd. All rights reserve
the end of 2006 was still very limited [2]. A similar situation
currently exists in Poland.
Salix is a diverse genus as regards biomass productivity,
capacity for heavy metal ions’ sorption and resistance [3e5].
Almost 20% of Salix taxa have features useful or essential in
biomass and contaminants accumulation. This is connected
withuseof theplants inmanythematicallydiversestudies [6,7].
The most important features are: high biomass productivity,
easy adaptation to new environmental conditions, relatively
high resistance to impurities present in soil and selective
cumulator plant, metallophyte that accumulates an exceptionallyed multiple of the concentration found in non-accumulators;nyl; Phytoremediation, use of plants to accumulate, remove orPH, total petroleum hydrocarbon.
d.
b i om a s s a n d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 4 1 0e1 4 1 8 1411
accumulation of contaminants [8e11]. Compared to other
plants Salix are quite effective as regards biomass productivity
[12,13]. At the same time, variation in biomass productivity is
observed within species [14e16]. Biomass production depends
on several factors, the most important of which are: site
conditions, andpresenceofpollutants [17e20]. Thesignificance
of biomass is all the more important that demand for Salix
materials as an energy source is increasing, but the use of
biomass has some limitations connected with the way of
exploiting it [21e23].
Some willow species have been found to be efficient in
absorbing: heavy metal ions, organic compounds (PAH, PCB,
TPH) and even selected explosives [7,24e28]. Like Populus, Salix
clones are characterized by wide differences in metal accu-
mulation dependent on structure as well as amounts ofmetals
available in the soil [29]. Hydroponic and environmental
studies show that phytoremediation by selected Salix clones
can be a useful tool in technical replenishmentmethods in soil
remediation [13,30]. Although Salix is not a hyperaccumulator
plant, a lot of clones can grow fast in heavily polluted areas
[31,32]. Salix growth in contaminated soil or amended mine
tailings can be assisted or restrained by soil conditions, the
presence of other plants orweather conditions [6,33]. Efficiency
of phytoextraction with Salix use in contaminated and uncon-
taminated areas among other things depends on: species or
even variety, soil conditions and plant age [25,31,34,35].
2. Materials and methods
2.1. Willow materials
Salix materials were collected from the salicarium belonging
to the Department of Silviculture, Pozna�n University of Life
Sciences. The salicarium consists of two parts. The first,
smaller part (0.2 ha), where materials were collected, is situ-
ated near Gaj Ma1y village, 40 km north-west of Poznan (the
co-ordinates of the middle of the salicarium are: 52� 390 24.6200
N, 16� 310 15.2300 E). The second, bigger part (0.4 ha), where
other Salix varieties were collected, is situated near Wielisla-
wice village (51� 150 14.3900 N, 18� 090 42.6200 E). The material in
the collection is mixed e from the wild and from breeding
program e and both parts of the salicarium have scientific
character only.
Two Salix species were tested e Salix viminalis and Salix
alba. All S. viminalis clones were planted on April 2005. Salix
alba clones were planted exactly one year earlier, as 20-cm
dormant cuttings, straight into the soil, without any prepa-
ration of the ground. The distance between rows was 0.5 m,
and the distance between shoots was 0.4 m in each row. The
area was not fertilized andweedsweremowed twice annually
in the first and second growing season only.
On January 2008 height and circumference at the base of all
shrubs were measured (72 shrubs totally, representing one
cultivar of S. alba and 8 cultivars of S. viminalis).
The following willow varieties were selected for further
analyses:
� S. alba var. Chermesina
� S. viminalis ‘1047’ (two samples e S.v. ‘1047’ and S.v. ‘1047’-a)
� S. viminalis ‘1053’
� S. viminalis ‘1054’
� S. viminalis ‘1056’
� S. viminalis ‘1057’
� S. viminalis ‘1059’
� S. viminalis ‘Turbo’ (two samples e S.v. ‘Turbo’ and S.v.
‘Turbo’-a)
� S. viminalis ‘Sprint’
(numbers and names in apostrophes refer to cultivated
varieties).
From all of the planted shrubs, the tallest shrubs and those
with the greatest diameter at the base of the trunk were cut
down on January 2008 and chosen for measurement of fresh
mass and dry mass, dried at a temperature of 105�C. In order
to preserve the collection it was necessary to leave other
measured shrubs uncut. It was assumed at the same time that
measuring the tallest shrubs and those with the greatest
diameter at the base of the trunk would show the maximal
production possibility in the given site conditions.
2.2. Location description
The terrain of the research area is flat and situated in the
lowland part of Poland. The upper layer of the ground is clay,
with the thickness of clay of 25 cm, brought from the nearest
excavation, and laid on the arable brown soil e one of the
most fertile types of soil in Poland.
The 25-cm clay layer is connected with the history of the
salicarium and was not laid owing to the described experi-
ment, but in the interpretation of results of this paper it is
important, due to the homogeneity of the soil substrate. The
clay was extracted and laid 2 years before planting of the first
willow shrubs, from the depth of 1e2 m below ground level.
An important factor limiting growth of plants is low annual
rainfall. According to data received from the meteorological
station in Zielonka, belonging to the University of Life
Sciences in Pozna�n, the average annual rainfall from the year
1986e2008 was 525.6 mm. When the investigated willows
were planted (2005) the annual rainfall was 468.3 mm (from
April 1st to September 30th 238.8 mm). In the next year
(2006) it was 512.5 mm (IV-IX: 335.3 mm), in 2007 it was
624.5mm (IV-IX: 308.4mm) and in 2008 it was 519.5mm (IV-IX:
233.0mm). This variability of rainfall in the years 2005e2008 is
similar to the trend observed in the long-term period.
2.3. Sampling
To the chemical analyses the plant material was collected in
the form of 10 cm parts of shoots from a height of 0.95e1.05 m
from 3 shrubs for each clone (1 sample from 1 shrub e total 3
samples for each clone). Material in the amount of about 100 g
fresh weight was placed in polypropylene vials. After being
transported to the laboratory the experimental material was
dried in an electric dryer for 72 h at a temperature of 105 �C.Material of approximately identical dimensions in terms of
the diameter and length of shoots was ground in an electric
ball mill. The fraction of sawdust used in the heavy metals
content analyses was 0.25e0.35 mm in size. Material was
mineralized in a closed Mars 5 Xpress microwave sample
b i om a s s an d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 4 1 0e1 4 1 81412
mineralization system by CEM using HNO3 and H2O2. Collec-
tion and transport of material for analyses were conducted
according to procedures described in PN-R-04031:1997 [36] and
PN-ISO 11464:1999 [37].
Soil samples were collected at the beginning of the experi-
ment at first from the entire studied area in order to determine
the degree of soil homogeneity. Taking into consideration
the exceptionally homogeneous character of the soil it was
sampled around specimens of individual genotypes, marking
a square of about 1 m2 around them. Soil material was
collected with a soil sampling tube (6 cm), and 25 soil drillings
were performed around each plant. Material was collected
from a depth of 0.25 m, then it was placed in polypropylene
containers and transported to the laboratory. After drying in an
electric dryer (105 �C and 96 h), grinding in a ball mill and
sifting through a sieve (mesh size 0.12 mm), three soil samples
(3 g) were extractedwith aqua regia according to the procedure
specified in Polish Standard PN-ISO 11466:2002 [38].
The bioaccumulation factors (BAFs) were calculated as the
ratio of heavy metal concentration in Salix shoots to concen-
tration of this metal in soil. Depending on BAF values, accu-
mulation efficiency was estimated using one of four groups:
1e0.1 (intensive), 0.1e0.01 (medium), 0.01e0.001 (weak) and
0.001e0.0001 (lack) [39]. Efficiency of studied heavy metals’
accumulation was determined by means of metal concentra-
tions in Salix shoots at the time of Salix planting (unpublished
data). The ranking of taxa was prepared based on the deter-
mination of the difference between heavy metal contents in
shoots, recorded in this study, and next a comparison of
accumulation between taxa.
2.4. Heavy metal analysis
The analysis of heavy metal contents in plant material and
soil was conducted by electrothermal atomization absorption
spectrometry (ETAAS) aswell as flame atomization absorption
spectrometry (FAAS) using an AA Varian Spectra 200 spec-
trometer. In all analyses hollow-cathode lamps (HCL) by Var-
ian and Perkin Elmer were exclusively used (lamps for one
element were used only). For each of themarked elements the
apparatus optimization procedure was performed, mainly in
a range of temperatures and times of individual stages of
analysis (ETAAS). To reduce the errors in matrix indication,
the deuterium background correction was applied. Contents
of selected heavy metals in willow sawdust were determined
within the procedures based on the guidelines for analyses of
environmental materials by atomic absorption spectrometry.
However, the analysis of soils was executed according to the
procedure described by Polish Standard PN-ISO 11047:2001
[40]. The selection of determined elements was the conse-
quence of an analysis of preliminary determination of twenty
metals by AAS techniques (ETAAS and FAAS as well as ICP-
OES and ICP-MS).
2.5. Wood analysis
Apart from heavy metal contents, physical and chemical
properties of wood were determined, such as the thickness of
completely dry wood (the stereometric method), the content
of minerals (ash), cold and hot water soluble substances (test
method T207 cm-08) as well as those soluble in an ethanol/
benzene mixture (1:1), contents of cellulose (according to
Seifert) and lignin (according to Komaroff) [41]
Experimental material (10 cm parts of shoots) after being
transported to the laboratory was dried and ground in an elec-
tric ball mill, the same as in the case of heavy metals. Sawdust
with a diameter of 0.30e0.43 mm was used for chemical anal-
yses of cellulose and lignin, while other parameters were
determined in the fraction of 0.49e0.75 mm.
To define differences between individual genotypes we
estimated the ratio of core, wood and also bark. Proportions of
bark, wood and core were estimated in 2 cm long fragments of
10 cm parts of shoots collected the same way as for selected
physico-chemical parameter analysis. Whole shoots were
weighed, debarked and mechanically separated into wood,
core and bark. All three fractions were weighed, dried at
105 � 5 �C for 24 h, seasoned in desiccators, the material was
weighed again and moisture was calculated. Percentages of
particular tissue contents (bark, wood and core) in shoots
were calculated based on constant weight of all three tissues
(water-free systems), according to which the total mass of
three Salix tissues is 1.
2.6. Soil analysis
During the experiment basic values of soil properties were
determined: active and replaceable acidity (PN-ISO 10390:1997)
[42], total content of organic carbon (PN-ISO 14235:2003) [43],
redox potential (EN-ISO 11271:2002) [44], granulometric anal-
ysis (PN-R-04032 [45]:1998, PN-R-04033:1998 [46]) and concen-
trations of studied heavy metals, as well as other metals that
play an important role in soil. The total content of potassium
was also measured by AAS method and magnesium according
to Schachtschabel’s method [47]. The analyses of assimilated
form of phosphorus content were done using the Egner-Riehm
method [47].
The soil was clayey with a great capacity for absorption of
water. Its favourable conditions are connected with the ability
of clay to absorb spring thaw water and store the water until
June,which isvery importantduringa springandearlysummer
drought period.
The analyzed soil is distinguished by low concentration of
heavy metals in comparison to the most frequent contents of
these metals in Polish soils. The soil characteristics are pre-
sented in Table 1.
2.7. Verification of obtained results
To minimize the error of the complex matrix, the deuterium
background correction was applied. The fresh standard curve
was delineated every day for the prepared standard solution
and sample solutions exhibiting concentrations within the
range up to 75% of the standard curve were prepared. Results
were validated on the basis of certified reference materials:
NIST 1575a (Pine Needles) and NCS DC 73350 (Leaves of
Poplar), analyzed in every tenth measuring set (Table 2), and
simultaneous analyses of randomly selected samples using
the ICP-OES method with a Vista MPX instrument by Varian
and the ICP-MS UltraMass-700. Two certified reference
Table 1 e Mean metal contents and physico-chemicalproperties of soil during the experiment and ranges ofselected heavy metals concentration in Polish soils.
Element Mean annualvalue
Concentration inPolish soilsa
Unit
C 0.411 � 0.028 e %
Ca 0.084 � 0.007 e %
Cd 0.623 � 0.048 0.2e0.8 mg kg�1
Cr 9.642 � 0.341 15e740 mg kg�1
Cu 7.482 � 0.052 5e23 mg kg�1
Fe 0.385 � 0.014 e %
Hg 0.023 � 0.001 0.05e0.2 mg kg�1
Mg 0.025 � 0.002 e %
Mn 0.038 � 0.002 0.024e0.057 %
N 0.043 � 0.003 e %
P 0.058 � 0.004 e %
Pb 6.105 � 0.175 10e25 mg kg�1
Zn 31.298 � 2.005 45e100 mg kg�1
Parameter Mean annual value Unit
pH H2O 5.32 � 0.04 e
pH KCl 4.24 � 0.03 e
Eh 284.38 � 16.24 mV
Porosity 29.74 � 2.05 %
Humidity 18.93 � 0.57 %
Conductivity 387.29 � 19.55 mS cm�1
Granulometric analysis
Fraction diameter [mm] Proportions of individualfractions [%]
2.0e0.5 11.2
0.5e0.25 15.31
0.25e0.10 19.79
0.10e0.05 8.7
0.05e0.02 13
0.02e0.005 8
0.005e0.002 11
<0.002 13
a data presented in Kabata-Pandias and Pendias (1993) as typical
range of elements concentration in Polish soil.
b i om a s s a n d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 4 1 0e1 4 1 8 1413
materials were used because of a lack of material exhibiting
certified values for each of the seven metals.
2.8. Statistical analyses
The experimental data were analyzed statistically with uni-
and multivariate methods. To examine the differences in
Table 2 e Comparison of results of heavy metal analyses [mg ktwo certified reference materials, NIST-1575a and NCS DC 733
Metals NIST-1575a (Pine Needles)
Certified value Authors’ result
Cd 0.233 � 0.004 0.232 � 0.009
Cu 2.8 � 0.2 2.84 � 0.18
Hg 0.0399 � 0.0007 0.0388 � 0.0011
Pb 0.167 � 0.015a 0.167 � 0.019
Zn 38 � 2 38.08 � 2.11
a reference values.
biomass productivity, structure and accumulation of heavy
metal ions for particular taxa, an analysis of variance for the
one-way classification was performed. Such an analysis
makes it possible to verify the general and specific hypotheses
concerning taxa (through the calculation of the least signifi-
cant differences, LSD at P < 0.05). In order to study the
differences between Salix taxa in respect of all heavy metals,
a multivariate analysis of variance (MANOVA) was conducted
[48,49]. For a graphic presentation of the tested clones with
regard to all five heavymetals jointly, a canonical analysiswas
used [4]. As a result of these analyses, the 5-dimensional space
(defined by the five heavy metals) was reduced with only
a slight loss of information to a plane described by the first two
canonical variates V1 and V2. The canonical variate analysis
(CVA) is closely connected with the partition of the F-statistic
used for testing the general multivariate hypothesis of no
differences in mean values of all studied heavy metals
between several taxa clones. To test the hypothesis that there
is no difference in mean values of the five heavy metals
between each two taxa clones, Mahalanobis distances were
calculated. Mahalanobis distance was suggested as a measure
ofmultivariate taxa clones’ similarity, whose significance was
verified by means of the critical value Da called “the least
significant difference”. On the basis of Mahalanobis distances,
calculated for all pairs of taxa clones, the shortest dendrite
can be drawn. For configuration of cloneswith regard to all ten
physico-chemical parameters of wood (only one observation
of each parameter for particular clones), principal compo-
nents analysis was performed [50].
3. Theory/calculation
Salix do not show a simple relationship between amount of
accumulated heavymetal ions and biomass productivity. That
is a result of different development of individual taxa
(biomass of Salix top ends) and the way of translocation of
heavy metal ions to different tissues. More than once it was
possible to observe the presence of Salix clones capable of
efficient biomass production without high accumulation of
metal ions. The reverse situation is also observed, but the
most frequent is the combination of those two observations.
During transpiration Salix accumulate water, including
metal ions, and their amount is probably regulated by defen-
sive mechanisms operating depending on pace of plant
growth.
gL1] on the basis of standard curve and after corrections by50.
NCS DC 73350 (Leaves of Poplar)
s Certified value Authors’ results
0.32 � 0.07 0.33 � 0.09
9.3 � 1.0 9.26 � 0.74
0.026 � 0.003 0.024 � 0.002
1.5 � 0.3 1.46 � 0.11
37 � 3 37.13 � 2.25
b i om a s s an d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 4 1 0e1 4 1 81414
4. Results
4.1. Biomass productivity
The investigated taxa are characterized by significant vari-
ability of biomass production (from 0.14 kg of fresh mass per
year per shrub of S. viminalis ‘1047a’, to 6.81 kg for one shrub of
S. alba var. Chermesina) (Table 3).
The ratio of dry mass to fresh mass was from 0.40 to 0.56
(the most frequent was 0.46).
4.2. Heavy metals in plants
Total concentration of selected heavy metals in individual
Salix shoots was significantly diverse. Results in mean values
are presented in Table 4.
In order to determine accumulation efficiency, bio-
accumulation factors (BAFs) for each taxon (Table 4) were
calculated and the ratio of accumulated metals in the plant
and in the soil was calculated. For tested clones only intensive
(I) or mean (M) accumulation was determined.
4.2.1. CadmiumThe higher cadmium accumulating plants were S. viminalis
‘1054’ and S. viminalis ‘1059’, while the least were S. viminalis
‘1056’ and S. viminalis ‘1047’. Taking the medium cadmium
concentration in the soil into consideration, Salix taxa were
characterized by high increase of metal concentration.
Differences in cadmium accumulation were over 85%; thus
they can be considered diverse. Accumulation of cadmium for
all clones was intensive, pointing to the significance of sorp-
tion dynamics.
4.2.2. CopperAccumulation of copper was at a medium level with the
exception of S. viminalis ‘1054’, this plant being the most
effective copper accumulating plant. The lowest concentra-
tion was observed for S. viminalis ‘1059’. The difference
between the highest and lowest metal concentration was
almost 90%.
Table 3 e Morphometric characteristics of investigated Salix al
Salix taxa Age(year)
High(cm)
Thicknessa
(cm)Fresh massof one shrub
(kg)(1
Salix alba var.
‘Chermesina’
4 634 7.0 27.24
S. viminalis ‘1156’ 3 452 5.5 12.790
S. viminalis ‘Sprint’ 3 451 6.0 6.670
S. viminalis ‘1053’ 3 371 5.1 3.140
S. viminalis ‘1047’ 3 402 4.6 2.745
S. viminalis ‘1054’ 3 393 3.0 2.765
S. viminalis ‘Turbo’ 3 335 4.0 2.395
S. viminalis ‘Turbo’a 3 352 4.2 2.430
S. viminalis ‘1059’ 3 407 3.5 1.125
S. viminalis ‘1057’ 3 341 3.1 1.005
S. viminalis ‘1047’a 3 357 2.3 0.405
a thickness at the base of trunk.
4.2.3. MercuryThemost intensively accumulatedmetal out of all metals was
mercury. The greatest mercury concentration was observed
for S. viminalis ‘1059’ and S. viminalis ‘1053’, and the lowest for
S. alba var. Chermesina and S. viminalis ‘Turbo’. The bio-
accumulation factor values were in a wide range, pointing to
significant diversity in individual Salix clones’ abilities to
accumulate mercury from soil. The difference in mercury
accumulation between extremes of high and low accumu-
lating taxa was over 160%.
4.2.4. LeadLead accumulation was at a medium level (BAF) with the
exception of S. alba var. Chermesina, this plant being themost
effective lead accumulating plant. The lowest lead concen-
tration was observed for S. viminalis ‘1047’a. It was lower than
for S. alba var. Chermesina by over 190%. Taking the similar
bioaccumulation factor values into consideration, the values
between the extremes of accumulation of cadmium by taxa
(190%) and also well known lead transport limited in the
rhizosphere, significant differences in lead accumulation by
individual Salix taxa were confirmed.
4.2.5. ZincAll taxa were capable of intensive zinc accumulation. The
greatest concentration of this metal was observed for Salix
viminalis Turbo’a, S. alba and Salix ‘1053’, and the lowest for
Salix ‘1047’a and Salix ‘1054’. The difference between taxa with
extremes of accumulation of zinc was over 35%. Taking metal
amounts in soil into consideration the differences in Salix
accumulation abilities were similar (except for aforemen-
tioned taxa).
4.2.6. All heavy metals jointlyThe most effective Salix taxa as regards accumulation of
all metals at the same time were S. viminalis ‘Turbo’a and
S. viminalis ‘1054’. Simultaneously, S. viminalis ‘Turbo’a was
the most effective plant for zinc and second for lead accu-
mulation. Selective accumulation of cadmiumand copperwas
observed for S. viminalis ‘1054’. That is particularly important
ba and S. viminalis largest individuals.
Dry mass05 �C) of oneshrub (kg)
Drymass/fresh
mass
Fresh mass ofone shrub/year
[kg]
Dry mass ofone shrub/year
[kg]
11.025 0.40 6.81 2.76
6.995 0.55 4.26 2.33
2.735 0.41 2.22 0.91
1.445 0.46 1.05 0.48
1.250 0.46 0.92 0.42
1.270 0.46 0.92 0.42
1.140 0.48 0.8 0.38
1.180 0.49 0.81 0.39
0.625 0.56 0.38 0.21
0.460 0.46 0.34 0.15
0.185 0.46 0.14 0.06
Table
4e
Conce
ntrationofse
lectedheavym
etals
[mgkgL
1]in
analyze
dso
ilandSalixsh
oots
andth
era
nkofclonesin
accum
ulationofallm
etals
sim
ultaneously.
Salixclone
Heavym
etal
Clone
position
Therankofth
em
ost
effectiveclonea
Therankofth
em
ost
effectivecloneb
Cd
Cu
Hg
Pb
Zn
Soil
0.623�
0.048
7.482�
0.052
0.023�
0.001
6.105
�0.175
31.298�
2.005
S.vim
inalis‘1047’
1.9834(I)
5.1842(M
)0.1290(I)
2.8392(M
)52.8259(I)
1S.vim
inalis‘Turb
o’a
S.albavar.
Cherm
esina
S.vim
inalis‘1047’a
2.4739(I)
5.9482(M
)0.1118(I)
2.3566(M
)46.5762(I)
2S.vim
inalis‘1054’
S.vim
inalis‘Sprint’
S.vim
inalis‘1056’
1.9472(I)
6.7877(M
)0.0960(I)
3.3764(M
)53.7994(I)
3S.vim
inalis‘1059’
S.vim
inalis‘1056’
S.vim
inalis‘1059’
3.4822(I)
4.0445(M
)0.1420(I)
4.8492(M
)56.2389(I)
4S.vim
inalis‘Turb
o’
S.vim
inalis‘1054’
S.vim
inalis‘1057’
2.7445(I)
5.4829(M
)0.1238(I)
3.3816(M
)50.7029(I)
5S.vim
inalis‘1053’
S.vim
inalis‘1053’
S.vim
inalis‘Turb
o’
2.4925(I)
6.4239(M
)0.0872(I)
4.9942(M
)57.1304(I)
6S.albavar.
Cherm
esina
S.vim
inalis‘Turb
o’
S.vim
inalis‘Turb
o’a
2.8237(I)
6.0821(M
)0.0995(I)
5.2814(M
)63.4672(I)
7S.vim
inalis‘Sprint’
S.vim
inalis‘1047’
S.vim
inalis‘1054’
3.6488(I)
7.6725(I)
0.1279(I)
3.4873(M
)48.4779(I)
8S.vim
inalis‘1057’
S.vim
inalis‘Turb
o’a
S.vim
inalis‘1053’
2.0036(I)
6.8247(M
)0.1328(I)
2.8342(M
)59.3849(I)
9S.vim
inalis‘1056’
S.vim
inalis‘1059’
S.vim
inalis‘Sprint’
2.0462(I)
6.2894(M
)0.0974(I)
4.0508(M
)56.9821(I)
10
S.vim
inalis‘1047’
S.vim
inalis‘1057’
S.albavar.
Cherm
esina
2.4837(I)
5.8745(M
)0.0532(I)
6.8372(I)
59.9242(I)
11
S.vim
inalis‘1047’a
S.vim
inalis‘1047’a
LSD
0.05
0.0262
0.0296
0.0280
0.0334
0.0338
Theletters
IandM
represe
ntacc
umulation:Ie
intensive(BAFs>
1),M
emedium
(1>
BAFs>
0.1)ofmetals
acc
umulation.
ataxaarrangedacc
ord
ingto
acc
umulationabilitiesdecreasingforallheavymetals
tested(byMANOVA)simultaneously.
btaxaarrangedacc
ord
ingto
acc
umulationabilitiesdecreasingforallheavymetals
simultaneouslytreatedto
plantbiomass
pro
ductivity.
b i om a s s a n d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 4 1 0e1 4 1 8 1415
because CdeCu antagonism is well known. Amounts of
accumulated metals and sorption of selective ions by indi-
vidual taxa, and their rank, are presented in Table 4. The taxa
were arranged according to decreasing capacities for accu-
mulation of particular heavy metals in relation to sorption of
all heavymetals simultaneously (*). The ranking was prepared
taking into consideration differences in studied heavy metals’
concentration in particular plants.
The data presented in Table 4 point to selective accumu-
lation of metals by selected taxa with simultaneous sorption
limited for other metals (an exclusion mechanism was
present in the majority of plants). The ability of Salix taxa to
accumulate all metals is considered simultaneously with
plant biomass productivity in the second ranking (**). This
rank well characterizes the studied taxa, because it takes
diversity of metal accumulation by different Salix parts into
consideration (unpublished results).
4.3. Physico-chemical parameters of wood
The results of selected physico-chemical parameters of Salix
taxa are presented in Table 5.
The greatest differences as regards bark, wood and core
content were in Salix shoots. Extreme values for those
parameters were: 45, 16 and 65%. The results are particularly
significant as regards bark (usually technological strap mate-
rial in industrial processing) and wood (valuable material in
wood-based industry).
Cellulose content was at below amedium level for the total
Salix population analyzed at the Salix plantation (unpublished
data) with the exception of two taxa: S. viminalis ‘Turbo’ and S.
viminalis ‘Sprint’. The determined cellulose content (respec-
tively 48.12 and 49.69%) with relatively low lignin content
(21.87 and 22.04%) and ash content (1.94 and 2.40%) could
point to great usefulness of those taxa in the paper industry.
Simultaneously, there were not large amounts of substances
soluble in all media and significant differences were found
between individual taxa (S. viminalis ‘Sprint’ and S. viminalis
Turbo’a).
4.4. Statistical analyses
4.4.1. Heavy metalsTesting of the detailed hypothesis allowed us to confirm that
the accumulation of individual metals by all eleven taxa
together was significantly diverse (P ¼ 0.01). Simultaneously,
accumulation of each metal by successive taxa individually
was significantly diverse with the exception of cadmium
accumulation by S. viminalis ‘1047’a and S. viminalis ‘Turbo’.
The greatest differences among accumulation by all taxa were
observed for zinc and next for: lead, cadmium and mercury.
The variable characteristics allowed determination of
changeability factors which decreased according to the
formula: Pb > Hg > Cd > Cu>Zn. Canonical analysis indicated
statistically significant diversity among Salix taxa as regards
accumulation of all metals. The differences among taxa are
presented in Fig. 1.
On thebasis ofMahalanobis analysis data presented in Fig. 1
were confirmed. Simultaneously, significant differences were
found in accumulation of all metals together by S. viminalis
Table 5 e Contents of selected soluble fractions, mineral substances, lignin, cellulose and proportional composition ofindividual parts of Salix shoots. Statistical characteristic.
Salix clone Fraction soluble in Ash[%]
Lignin[%]
Cellulose[%]
Percentage in shoots [%]
Coldwater [%]
Hotwater [%]
EtOH/benzene[%]
Bark Wood Core
S. viminalis ‘Sprint’ 0.22 0.66 3.02 2.40 22.04 49.69 27.95 71.17 0.88
S. viminalis ‘Turbo’ 1.04 1.53 3.51 1.94 21.87 48.12 29.68 69.44 0.88
S. viminalis ‘1057’ 1.42 2.04 3.13 1.95 22.89 44.17 33.67 65.62 0.70
S. viminalis ‘1056’ 2.19 2.72 3.42 2.07 20.63 43.95 27.53 71.77 0.70
S. viminalis ‘1054’ 1.97 2.22 4.94 2.34 21.49 43.17 27.66 71.59 0.75
S. viminalis ‘1053’ 1.61 2.25 3.25 1.88 22.32 42.88 31.96 67.16 0.88
S. viminalis ‘Turbo’a 2.48 2.41 4.75 2.15 20.57 42.85 27.88 71.19 0.93
S. viminalis ‘1047’a 1.29 2.27 3.82 2.12 21.36 42.83 28.99 69.84 1.16
S. alba var.
Chermesina
2.01 2.59 3.49 1.91 21.48 42.74 23.10 76.13 0.77
S. viminalis ‘1047’ 1.48 2.46 4.75 2.18 20.74 42.37 27.21 71.78 1.01
S. viminalis ‘1059’ 1.87 2.89 4.28 2.01 21.53 42.09 28.73 70.22 1.05
Mean � SD 1.60 � 0.62 2.19 � 0.62 3.85 � 0.71 2.09 � 0.17 21.54 � 0.72 44.08 � 2.49 28.58 � 2.71 70.54 � 2.71 0.88 � 0.15
Coefficient of
variation [%]
38.88 28.44 18.35 8.25 3.36 5.64 9.49 3.85 16.84
b i om a s s an d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 4 1 0e1 4 1 81416
Turbo’a without consideration of biomass productivity for
individual taxa.
4.4.2. Physico-chemical parameters of woodTo indicate the differences in individual wood parameter
values principal components analysis was performed. The
analysis is closely related to the canonical variates analysis. In
Fig. 2, Salix taxa are plotted in the space of the first two prin-
cipal components.
As the result of transformation of the ten original variables
(physico-chemical parameters) into two new variables (prin-
cipal components) the loss of information is equal to about
35%. However, more than 65% of variation indicates the
general tendency in differentiation of clones.
The greatest differences as regards including all parame-
ters were observed between S. viminalis ‘Sprint’ and S. alba var.
Chermesina taxa, and also between S. viminalis ‘1056’ and S.
viminalis ‘1057’. In the first case the substantial diversity
probably resulted from significant differences in cellulose and
ash content and also the difference in wood and bark content.
In the case of S. viminalis ‘1056’ and S. viminalis ‘1057’ taxa the
Fig. 1 e Graphical representation of Salix taxa in the space
of the first two canonical variates with the shortest
dendrite superimposed on it and determined on the basis
of Mahalanobis distances.
differences were significant for all studied parameters. It is all
the more interesting that such significant differences in wood
structure did not correspond to differences in heavymetal ion
accumulation by individual taxa.
5. Discussion
Usually the results of biomass production from the willow
plantations are given per hectare per year. In the present
research single shrubs were investigated. This means that the
obtained results should bemultiplied by the number of shrubs
growing on 1 ha. Most often 10e20 thousand willow cuttings
are planted on such an area. If the results are multiplied by
10 000, this means 1e68 tonnes per ha per year of fresh mass
could be obtained (0.46e27 tonnes of dry mass/ha/year). But it
is necessary to emphasize that the results were obtained from
the best growing shrubs, from the best growing taxa. This
means that the real results for the average willow plantations
must bemuch lower.Moreover, results recorded for individual
shrubs may not be directly multiplied by 10 000 or particularly
20 000. This results from the mechanism of competition,
Fig. 2 e Graphical representation of individual wood
parameter values for Salix taxa in the space of the first two
canonical variates.
b i om a s s a n d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 4 1 0e1 4 1 8 1417
which appears when the number of plants per unit area
increases. Willows in the salicarium grow in a smaller spacing
than shrubs grown at commercial plantations of fast-growing
species. Having more space they produce a greater biomass,
as e.g. S. alba, which producing the highest biomass occupied
in this study an area of approx. 4 m2. Such a spacing corre-
sponds to 2500 plants per ha. In such a case it would yield, at
the biomass obtained by S. alba, 17 t of fresh and 7 t of dry
matter per ha annually. Here it also needs to be stressed that it
is the best result, not only among all the analyzed clones, but
also among all examined shrubs in each of the clones, at the
same time not exceeding 7 t of dry matter per ha, which is
considered the profitability threshold in the production of
biomass.
6. Conclusions
The use of tested willow taxa on a wide scale solely as sources
of biomass for energy purposes may prove to be economically
unjustified. Single, best growing specimens (S. alba var. Cher-
mesina), growing under highly favourable conditions, yielded
drymatter, which did not exceed 7 t per 1 ha. However, locally
S. alba may constitute a valuable source of wood, which
proportion in relation to bark and the core was highest among
all the tested willows, at the simultaneous very low ash
content.
The use of tested plants as phytoremediators may turn out
to be promising. In this respect S. viminalis ‘Turbo’ proved to be
best, although in terms of biomass increment higher amounts
of heavy metals may be accumulated by S. alba.
From the point of view of pulp and paper industry, Salix
viminlis ‘Sprint’ seems to be most promising among the tested
cultivars, as it was characterized by the highest cellulose
content.
Acknowledgements
The experimental part of this study was supported by the
Ministry of Science and Higher Education (State Committee
for Scientific Research KBN), Grant No. N N 305 372538.
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