沙漠研究 23-4, 167 -172 (2014 )－APCSEET2013 Refereed Papers－

Journal of Arid Land Studies

Preliminary Study of Phytoremediation and Biomass Production
by Salix Species on Abandoned Farmland Polluted with Heavy Metals
Yuichi ISHIKAWA *1), Satomi SATO1), Yasuji KURIMOTO2), Hajime YAMADA2),
Atsushi HAYAKAWA1) and Shin HIDAKA1)
Abstract: The objective of this study was to clarify the growth properties of Salix species on abandoned farmland polluted withheavy metals in order to use such an area for cultivation as well as land remediation. Four clones of willow, Salix pseudolinearis(FXM), S. pet-susu (HB471, KKD), and S. sachalinensis (SEN) were cultivated within two sites ("HM" and "LHM") with different
heavy metal content. AT site HM, the total Cd was 2.57 ± 0.18 mg/kg dry weight (DW) and total Zn was 227 ± 22 mg/kg DW, andat site LHM, the total Cd was 0.114 ± 0.036 mg/kg DW and total Zn was 3.48 ± 0.96 mg/kg DW. The fresh weight of Salix after one
season of growth at site HM was approximately one-thousandth that of plants at LHM. The poor growth in HM was due to dry soil
lacking plastic mulch. KKD was the fastest growing of the four clones at both sites. Although soil Cd and Zn content at site HM
was approximately 22-92 times higher than their corresponding content at site LHM, the range of heavy metal content of plants at bothsites was almost the same. The accumulation capability differed. Of the four clones, FXM showed the highest Cd and Zn content.
Compared with hyperaccumulating plants (Arabidopsis halleri ssp. gemmifera), FXM salvaged 38.9% of the Cd accumulated by thehyperaccumulator, even when the site was contaminated with only low levels of heavy metal. We concluded that the FXM clone
performed the best as a heavy metal collector, and the KKD clone was the best for biomass production.
Key Words: Biomass production, Phytoremediation, Salix, Willow.

1. Introduction
As the combustion of fossil fuels is becoming widely
understood as resulting in both global warming and exhaustionof these fuels, there is increasing focus on biomass as a sourceof renewable energy. C4 plants such as maize or sugarcane
are well known as energy crops; however, it is a concern that
their use conflicts with food security because of their highvalue as staple foods. Therefore, lignocellulosic feedstocks
offer the potential to provide “second generation” biofuels(Simpson-Holley et al., 2007, Naik et al., 2010) because they
are free from conflicting demands for food. Willow, seaweed,
galingale, Japanese pampas grass, sunflower, and rape seed arelisted as second generation biomass crops in Japan (EXResearch Institute, 2011a).
In Sweden and Canada, willow species have already beenused to produce commercial fuel (Juga et al., 1999). Use ofthis biomass is currently limited to direct combustion andformation of biogas, though fermentation for bioethanol
production is being studied (Sassner et al., 2006). Willow
and Salix species are widespread in the Northern Hemisphereand can grow in diverse environments. Various trials havebeen conducted for use of willows as biomass resources inJapan. In Hokkaido, some studies on a business model for
cultivation and ethanol production from willow have been
carried out (Hokkaido Development, 2011, Orihashi et al.,2012). A trial in Saitama was conducted to convert a boiler
from heavy oil/coal oil to wooden chips in greenhouses forhorticultural use and to grow willow on abandoned farmlands
as sources of wooden chips (EX Research Institute, 2011b).
In the cold climate of the southern Tohoku region, Mitsui et al.
(2010) selected four superior clones for biomass production.
Along with an increase in the average age of farmers, thearea of abandoned paddy fields in Akita Prefecture increased
from 4,002 ha in 2000 to 6,789 ha in 2005. Most farmers
renounced cropping rice not only because of their age, but also
because of falling rice prices. Abandoned farmland can cause
problems such as the spread of pests and weeds to neighboring
farms, wild animal invasion, and difficulties managing
irrigation and drainage facilities; therefore, it is critically urgent
to develop other uses for the abandoned land to maintaincommunity environments.
Heavy metal contamination of cropland and pollution ofagricultural products are other environmental problems founddownstream of mining areas worldwide. In the case of Japan,
7,575 ha of agricultural land has been assigned as polluted
areas due to contamination with heavy metals, especially Cd,（Received, September 21st, 2013; Accepted, January 17th, 2014）* Corresponding Author: yu_ishikawa@akita-pu.ac.jp
241-438, Shimoshinjo-Nakano, Akita-Shi , 010-0195, Japan
1) Faculty of Bioresource Sciences, Akita Prefectural University

2) Institute of Wood Technology, Akita Prefectural University

of which 794 ha remain untreated (Environment Management
Bureau, Department of Environment, Japan, 2012).
A main countermeasure to heavy metal contamination ofsoil is covering the land with unpolluted soil; however, this isincreasingly difficult because of a lack of fresh soil. Anothertechnology for land rehabilitation from pollution is
phytoremediation. Willow species have been selected forphytoremediation of heavy metal pollution in some studies(Berndes et al., 2004; Maxted et al., 2007). On the other
hand, very few trials have been conducted with willow
plantations for phytoremediation in Japan.
From the above background, use of heavy metal polluted
land for biomass resource production is meaningful for both
agricultural land rehabilitation and use of the land for
production of inedible species. The objective of this study
was to clarify the growth properties of Salix species on heavy
metal polluted abandoned farmland in order to use the area for
cultivation as well as land remediation.

Table 1. Typical topsoil properties at the two experimental sites.
Site

HM

LHM

Soil type

Gray Lowland Soil

Gray Lowland Soil

pH (H2O)

6.26 (0.059)

6.53 (0.028)

Total C*mg/g

0.329 (0.032)

0.111 (0.003)

Total N*

mg/g

0.0273 (0.0028)

0.0111 (0.0040)

Total Cd**mg/kg

2.57 (0.184)

0.114 (0.036)

Total Cu**

mg/kg

1070 (232)

N.T.***

Total M n**

mg/kg

1200 (304)

N.T.***

Total Zn**

mg/kg

227 (22.2)

3.48 (0.958)

The values in parentheses mean standard deviation.
*: Total carbon and nitrogen were determined by combustion method.
**: Total Cd, Cu, M n, Zn were determined by an ICP atomic emission
spectrometer (ICAP 6000, Thermo Fischer Scientific, K. K.).
***: Not tested.

season, no irrigation was used. The whole shoot wascollected to survey growth before new sprouts emerged in
April 10, 2012.

2. Materials and Methods
2.1. Site outline
Two sites were selected for study; one site is a heavy metal
contaminated area previously used for rice cropping in Daisen
city, Akita Prefecture, Japan (site HM) and the other site is a
low-pollution fallow land, used as a control, at the Center ofField Education & Research, Akita Prefectural University,
Ogata village, Akita Prefecture, Japan (site LHM). Typical
topsoil properties of the two sites are shown in Table 1. The
heavy metal content at site HM was total Cd 2.57 mg/kg DW
and total Zn 227 mg/kg DW, and at site LHM was total Cd
0.114 mg/kg DW and total Zn 3.48 mg/kg DW.
2.2. Salix cultivation
Four clones of Salix were cultivated in the study: Salix
pseudolinearis (FXM), S. pet-susu (HB471), S. pet-susu(KKD), and S. sachalinensis (SEN), selected by Mitsui et al.
(2010). Branches were cut into 30 cm long segments 2-7days before transplanting. Cuttings of each clone were stuck
into soil up to 20 cm deep in the ground. At site HM,
cultivation started May 8, 2012 with no fertilizer. Threecuttings of each clone were planted randomly at one-meterintervals. Insecticide was applied around each stem on July
31. During the growing season, no irrigation was used. The
whole shoot was collected on October 15. At site LHM,
cultivation started May 8, 2010, without fertilizer but withplastic mulch. For each clone, 66 cuttings were placed at 0.5
m intervals with 1.4 m between clones (i.e. a planting densityof 12,000 trees per hectare). Insecticide was applied aroundthe stem in July of 2010 and 2011. During the growing

2.3. Sample preparation and analysis of heavy metal
content
At site HM, collected shoots were divided into leaves andstems, and the fresh weight was measured before oven-drying.
The samples were dried in a 70°C oven for 3 days before
determining dry weight, and then cut with scissors into 2-3 cm
sections. The samples were powdered with a ball mill. At
site LHM, collected shoots were divided into timber and bark
and were air-dried in a greenhouse for a week, then weighed todetermine fresh weight. Dry samples were weighed again to
determine dry weight and were then milled with a cutting milland sieved through a 40-100 µm mesh. Litter was collected
between lines of clone of KKD and FXM on the same day,April 10, 2012. Fresh weight and dry weight were
determined in the same manner as timber and bark. Dry
leaves were powdered with a coffee mill.
Samples were digested with nitric acid and perchloric acidon a hot sandbath. Cd, Mn, and Zn contents were determinedwith an ICP mass spectrometer (ICAP Q, Thermo Fisher
Scientific, K. K.). Uptake of Cd, Mn, and Zn was calculated
as dry weight multiplies by each heavy metal contents.

3. Results and Discussion
3.1. Growth of trees
The fresh weight of the four Salix clones at the two sites isshown in Table 2. The fresh weight in site HM ranged from
0.44 to 3.6 g per a plant was approximately a thousandth lower
than those in LHM ranged from 0.7 to 1.5 kg per a plant.
Salix species are known as a fast growing species and thus

Table 2. Fresh weight of four clones of Salix at two sites.

g/plantg/plant

kg/plant

kg/plant

FXM *
HB471

0.44
2.6±2.4

0.19
1.7±2.1

0.8±0.3
1.0±0.3

9.3±5.5
7.9±1.1

KKD
SEN

3.6±2.8
2.5±0.5

4.5±3.4
2.5±0.2

1.5±0.6

14.6±3.7

0.7±0.3

8.1±1.8

The values show means±standard deviation.
* Only one FXM cutting at site HM survived during the study.

trees in LHM showed same ranged growing as other trials(Mitsui et al., 2010). Heavy metal content may affect anegative effects on their growth, however in another trial withplastic mulch adjacent to the site HM, all the four clones
showed the almost same growth (2.02, 1.83, 2.31 and 2.14 mof height for FXM, HB471, KKD and SEN, respectively foreleven month growing) as in LHM (2.1, 1.8, 2.7 and 2.2 m ofheight for FXM, HB471, KKD and SEN, respectively for

Heavy metal content(mg/kg)

Site LHM
1st year stem 2nd year stem

Heavy metal content(mg/kg)

stem

Site HM
leaf

Heavy metal content(mg/kg)

Line

a) Cd

8
7
6
5
4
3
2
1
0

b) Mn
40
30
20
10
0

c) Zn
200
150
100
50
0

FXM

HB471

KKD

SEN

Leaf Stem Leaf Stem Leaf Stem Leaf Stema) Cd

Heavy metal content(mg/kg)

10
8

and stem of four Salix in site LHM. Error bar means

6

standard deviation.

4
2

Heavy metal content(mg/kg)

f

0

800

b) Mn

700
600
500

twelve month growing). Therefore the poor growth in HM
caused from soil water condition being dry because of lack ofplastic mulch in the moment.
KKD grew the fastest of the four clones at both sites. As
Mitsui et al. (2010) concluded, KKD produced the mostbiomass; the tendency of growth for the four clones was thesame at the two sites.

400
300
200
100
0

160

c) Zn

140

Heavy metal content(mg/kg)

Fig. 2. a) Cadmium, b) manganese, and c) zinc content in leaf

120
100
80
60
40
20
0
FXM_leaf
FXM_stem
HB471_leaf
HB471_stem
KKD_leaf
KKD_stem
SEN_leaf
SEN_stem

FXM

HB471

KKD

SEN

Leaf Stem Leaf Stem Leaf Stem Leaf Stem
Fig. 1. a) Cadmium, b) Manganese, and c) zinc content in leaf
and stem of four Salix in site HM. Error bar means
standard deviation.

3.2. Heavy metal content in Salix
Figures 1 and 2 show the Cd, Mn, and Zn content in thefour Salix clones at site HM and LHM, respectively. The
content of Cd and Zn was very similar in every clone. At siteHM, the content ranged from 2.8 mg/kg in stems of SEN to 8.1
mg/kg in stems of FXM for Cd and from 30.3 mg/kg in leavesof HB471 to 135 mg/kg in leaves of FXM for Zn. At site
LHM, the content ranged from 0.5 mg/kg in timber of KKD to
4.8 mg/kg in bark of FXM for Cd and from 10.7 mg/kg in
timber of KKD to 157 mg/kg in bark of FXM for Zn. Cd andZn belong to the same group of elements, therefore, their
behavior is quite similar. Plants take up Cd by the same
pathway as Zn; consequently, plants tend to accumulate acertain level of Cd if Cd is present in the soil. The Mncontent showed a different trend from those of Cd and Zn.
The soil Cd and Zn content at site HM were respectively
approximately 10 and 30 times higher than at site LHM,
whereas the range of content of these heavy metals in plants at

a) CdUptake of heavy metal (mg/pl ant)

7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
FXM

KKD

SEN

Lines

b) Mn

180

Uptake of heavy metal (mg/pl ant)

HB471

160
140
120
100
80
60
40
20
0
FXM

HB471

KKD

SEN

Lines
c) Zn

Uptake of heavy metal (mg/pl ant)

120
100
80
60
40
20
0
FXM

HB471

KKD

SEN

Lines

Fig. 4.

Uptake of a) cadmium, b) manganese, and c) zinc by fourSalix in site LHM.

have differently shaped leaves; therefore, the different range ofaccumulation may be a result of the shapes of their leaves.

Fig. 3. Uptake of a) cadmium, b) manganese, and c) zinc by fourSalix in site HM.

both sites was almost the same. However, the accumulation
capability differed among cultivars and clones. Maxted et al.
(2007) reported the results of field trials of phytoremediation
by S. caprea × cineria × viminalis on soil that contained
41.6±0.58 mg Cd/kg and 2418 ± 81.8 mg Zn/kg; the plants
contained 8.20 mg/kg Cd and 12 mg/kg Zn. Compared to thestudy by Maxted et al. (2007), the four clones we tested
showed from one-tenth to the same range of heavy metal
content, although the soil content was 20 to 40 times lower.
In the four clones, FXM showed the highest Cd and Zn content.
Harada et al. (2010) reported that Salix accumulates Cd and Zn
at the tips of the serrations in leaves. The four Salix lines

3.3. Cd uptake by Salix
Figures 3 and 4 show Cd, Mn, and Zn uptake in the fourSalix lines at sites HM and LHM, respectively. At HM,
uptake of Cd and Zn was very similar in every clone. At siteHM, uptake of Cd was in the order KKD > HB471 > SEN >>FXM and uptake of Zn was KKD > SEN > HB471 > FXM,
whereas at site LHM, uptake of Cd was FXM > KKD >HB471 > SEN and uptake of Zn was FXM = SEN > HB471 >KKD. The heavy metal uptake at site HM was exponentiallysmaller than at site LHM because of the difference in plant
growth between the sites. The difference in the order
between the four clones arose from the growth performance at
HM; in particular, FXM grew only to one-fifth the weight ofthe others.
The salvage of heavy metals from the soil can be calculated
by multiplying the uptake of heavy metals by planting density.

The salvage of Cd from site LHM amounted to 77, 26, 43, and
4.0 g Cd/ha by clones FXM, HB471, KKD, and SEN,
respectively. Ishikawa et al. (2009) found that 199 g/ha of Cd
was collected by hyperaccumulating plants (Arabidopsis
halleri ssp. gemmifera) from site HM. FXM salvaged 38.9%of the Cd at site LHM, as high as the hyperaccumulator, evenwhen the site was only contaminated with low levels of heavy
metals.
One use of Salix biomass is as material for formation ofparticle board. Yamada et al. (2013) produced willow
particle board from wood chips obtained in the first year of
cropping at site LHM, and reported that willow particle board
showed a lower modulus of elasticity and modulus of rupture,
but the same internal bonding strength and thickness swellingon water absorption compared to cedar boards. Direct
combustion is another option for its use, but these boards
contain more heavy metal than common boards; i.e. Ono(2005) showed that the median heavy metal content in woodchips from construction waste is 0.05 mg Cd/kg, 45 mg Mn/kg,
and 29 mg Zn/kg. Use as particle board is preferable to avoid
the chemical hazards of combustion.

4. Conclusion
All four clones selected in this study showed growthcomparable to that found in previous studies and a yield ashigh as >10 t/ha･y, even in a cold snowy area in the northern
Tohoku region when appropriate treatments such as mulchingwere given. From the viewpoint of phytoremediation, theFXM clone was concluded to be the best accumulator of heavy
metals because its heavy metal content was almost five times
that of the other three clones. To produce the maximum
biomass, the KKD clone was the best because it had thehighest plant weight.
The study did not prove
phytoremediation performance directly in heavy metal
contaminated land; therefore, further study is needed to clarify
whether the performance can be maintained on such land.

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