evaluating silicon concentrations in biofuel feedstock crops miscanthus and switchgrass
TRANSCRIPT
b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 3
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Evaluating silicon concentrations in biofuel feedstock cropsMiscanthus and switchgrass
Krishna P. Woli a, Mark B. David a,*, Jenwei Tsai a, Thomas B. Voigt b, Robert G. Darmody a,Corey A. Mitchell a
aUniversity of Illinois at Urbana-Champaign, Department of Natural Resources and Environmental Sciences, W-503 Turner Hall, 1102 S.
Goodwin Av., Urbana, IL 61801, USAbUniversity of Illinois at Urbana-Champaign, Department of Crop Sciences, S-416 Turner Hall, 1102 S. Goodwin Av., Urbana, IL 61801, USA
a r t i c l e i n f o
Article history:
Received 19 July 2010
Received in revised form
7 February 2011
Accepted 4 March 2011
Available online 3 April 2011
Keywords:
Miscanthus � giganteus
Panicum virgatum
Combustion
Precipitation
Silicon
Temperature
* Corresponding author. Tel.: þ1 217 333 430E-mail address: [email protected] (M.B
0961-9534/$ e see front matter ª 2011 Elsevdoi:10.1016/j.biombioe.2011.03.007
a b s t r a c t
Silicon (Si) concentrations in biofuel feedstock crops have a critical role in combustion
processes. The purpose of this study was to quantify Si concentrations in plant biomass
samples and to evaluate the contributing factors for Si concentrations. We determined
total Si concentrations in Miscanthus � giganteus (M. � giganteus) collected from various
research trial plots in the eastern U.S. and in Miscanthus spp. and Panicum virgatum, ‘Cave-
in-Rock’ (switchgrass) from an additional eight trial plots established across Illinois. Whole
aboveground plant biomass at each site were air-dried and ground. Total Si concentrations
in plant samples were determined by dry-ashing plant tissue in a muffle furnace, followed
by alkaline fusion and then colorimetric analysis. Average Si concentrations in statewide
M. � giganteus plant samples ranged from 0.72% to 1.6% and samples from within Illinois
ranged from 0.55% to 2.4%. The overall median value of concentrations in M. � giganteus
samples among all sites was 1.08%. The median value in switchgrass samples (1.5%) was
1.4 times higher than that for M. � giganteus. Among six other Miscanthus spp. samples
from the Urbana trial plot in Illinois, Si concentrations were about 1/3 that of
M. � giganteus. Variation in Si concentrations tended to be associated with temperature and
precipitation of the location where the biofuel crops are being grown. We did not find any
relationship between soil type and plant Si concentrations. Long-term evaluations of soil
mineral concentrations and additional environmental factors are required to better
understand the contributing factors for Si concentrations.
ª 2011 Elsevier Ltd. All rights reserved.
1. Introduction Biofuels could reduce greenhouse gas emissions by 1.7 billion
A major fraction of global CO2 emission is from burning fossil
fuels that supply 85% of the total energy consumption [1], and
there is growing concern for developing viable alternatives to
non-renewable fossil fuels. Direct combustion of biomass is
reported to be the most energy-efficient alternative with the
highest potential for mitigating the CO2 emission problem [2].
8.. David).ier Ltd. All rights reserved
tons per year, which is equal to more than 80% of trans-
portation-related emissions and 22% of total emissions [3].
Relative to the fossil fuels they are capable of displacing,
greenhouse gas emissions are reduced 12% by the production
and combustion of ethanol and 41% by biodiesel [4]. The U.S.
Department of Energy has targeted developing biomass
conversion technologies since petroleum products are the
.
b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 32808
most limiting primary fossil energy resources, and conversion
of plant biomass provides the only anticipated renewable
feedstock to generate liquid transportation fuel [5]. The
plant materials-derived fuels can be cost-competitive with
gasoline and diesel, and can reduce global warming emis-
sions, improve air quality, reduce soil erosion, and diversify
agroecosystems [3,6].
Energy and fuels from biomass could provide tremendous
economic, environmental, and energy security. Perennial
grasses are burned to produce heat and electricity or treated
with enzymes, heat, and/or acids to produce sugars that can
then be used to produce cellulosic ethanol [7]. Such grasses
have been termed as biofuel feedstock crops which require
much less energy and financial inputs than annual arable
crops. Miscanthus � giganteus (M. � giganteus) is one of several
ideal biomass crops that can be used to generate heat, power,
and fuel, and can alleviate CO2 emissions [8,9]. It is a perennial
C4 grass with high yield potential [9,10], efficient conversion of
solar radiation to biomass, efficient use of nitrogen and water,
and good pest and disease resistance [11,12], considered as
a low input crop having a low environmental impact
[1,9,12,13]. Among other biofuel feedstock crops, the nitrogen,
energy, and land use efficiencies inM.� giganteus are reported
to be highest at the lowest nitrogen inputs [14]. The ratio
of energy output to energy input in the production of
M. � giganteus is 14.2e19.7 and thus much better than that of
whole grain crops at 8.5 [15]. Compared to other lignocellulose
plants, M. � giganteus biomass is reported to have a good
combustion quality [2].
The mineral concentration of herbaceous biomass has
a great impact on its suitability as a feedstock for thermo-
chemical combustion processes [16,17], and reduced mineral
content at harvest improves the combustion characteristics of
biomass [18]. Thermochemical conversion in a gasification
reactor involves heating the feedstock under restricted
oxygen conditions to produce syngas that is subsequently
converted to an energy product [19]. Biomass quality can
drastically impact the net energy output, both by influencing
the effectiveness of conversion plants and controlling the
heating value [16,20]. At operational temperatures where
carbon conversion efficiency is high, silicon (Si), which is
abundant in grass feedstocks, and sulfur react with aluminum,
chlorine, potassium, and other alkalis to form sticky glass-like
silicates and oxides referred to as slag, along with corrosive
alkali sulfates [21]. These ashes and inorganic elements
produced during combustion react to form slag deposits and
corrosive compounds at temperature in the range of 700 �C[16,22] and may cause a number of serious problems to power
plants through slagging, corrosion, and fouling [20]. Slag
formation and corrosive alkalis increase maintenance cost,
reduce the lifespan and utility of gasifier hardware, and
diminish economic feasibility of converting these feedstocks
to fuel [21]. Although Si can negatively impact thermo-
conversion of biomass to bioenergy, Si has beneficial biolog-
ical effects, including increased plant resistance to lodging
and drought [23], improved disease resistance [24,25], insect
and nematode resistance [26], soil nutrient availability,
nutrient balance within the plant (e.g., N, P, Zn, and Mn),
photosynthesis, improved reproductive fertility, and reduced
transpiration [27].
With respect to the role on the effectiveness of the ther-
moconversion process, minimizing mineral contents and
understanding their controlling factors is important in
a biofuel crop. However, relatively few studies have assess-
ed Si concentration in the heavily studied biofuel crops
M. � giganteus and Panicum virgatum (switchgrass). The
objectives of our study were to quantify Si concentrations and
to evaluate the controlling factors for Si concentrations in
M.� giganteus plant samples that were collected frombiomass
trial plots in the eastern U.S. Silicon concentrations, that were
determined for six other different varieties of Miscanthus spp.
and several ‘Cave-in-Rock’ switchgrass plant samples collected
from various trial sites in Illinois, were also included in the
study for comparison.
2. Materials and methods
The existing research trial plots established by the Illinois
Council for Food and Agriculture Research, University of Illi-
nois Energy Biosciences Institute, and Department of Energy/
Sun Grant Herbaceous Feedstock Partnership were used for
collecting plant biomass samples. M. � giganteus plant
samples were collected from biomass trial plots in Michigan,
Nebraska, New Jersey, Kentucky, Oklahoma, and Mississippi
in January 2010. Similarly, plant samples were collected in
December 2007 from eight Research and Education Centers
located at Dekalb, Havana, Urbana, Orr, Pana, Brownstown,
Fairfield, and Dixon Springs in Illinois. Four 10 � 10 m repli-
cated side-by-side trials of M. � giganteus and ‘Cave-in-Rock’
switchgrass have been established at Dekalb, Urbana, and
Dixon Springs in 2002 and at Havana, Orr, Pana, Brownstown,
and Fairfield in 2004 (Table 1) in Illinois along a longitudinal
gradient at these sites without fertilizer additions to examine
the response of these crops following the conversion from row
cropping [28]. Trial plots of aM.� giganteus fertility study were
established at Nebraska, New Jersey, and Kentucky in 2008
and unfertilized plots at Michigan, Oklahoma, and Mississippi
in 2009. Four sets of plant biomass samples were collected
from each location ensuring one from each replicated plot and
were used for Si analysis. Therefore, we had four replicates
per site, with each replicate analyzed in duplicate (see below).
Soil types ranged from Alfisols at Kentucky and Michigan,
Mollisols at Oklahoma and Nebraska, Ultisols at Mississippi
andNew Jersey to both Alfisols andMollisols at various sites in
Illinois (Table 1).
Whole plant samples were collected randomly from
different replicate plots at the senescence stage of plant
development. The collected plant materials were air-dried
and were ground in a Wiley mill (Arthur H. Thomas Co.,
Philadelphia, U.S.A.) and passed through 40-mesh screen
before analysis.
Total Si concentrations in plant samples were determined
using a ‘modified Hallmark’ procedure (Si determination
technique) developed by Hogendorp [29]. In general, this
technique involved dry-ashing plant tissue in a muffle
furnace, followed by alkaline fusion, and then colorimetric
analysis. Plant tissue samples (25 mg) were ashed in nickel
crucibles without covers at 550 �C for 5 h in a muffle furnace
(Hythermco, Pennsauken, NJ, U.S.A.). Sampleswere left to cool
Table 1 e Physical characteristics of the sites established for Miscanthus fertility study in the U.S., by latitude (north tosouth).
State/Location/Latitude
Planted year Soil type Soil class Mean annualtemperature/precipitation
MI/MSU Kellogg
Biological Station
42.3956359 N
2009 Kalamazoo loam (Alfisols) Fine-loamy, mixed, semiactive,
mesic Typic Hapludalfs
8.9 �C89.3 cm
IL/Dekalb
41.8441175 N
2002 Elpaso silty clay loam (Mollisols) Fine silty, mixed, superactive,
mesic Typic Endoaquoll
8.8 �C94.9 cm
NE/Univ. of Nebraska
41.1720000 N
2008 Tomek silt loam (Mollisols) Fine, smectitic, mesic Pachic
Argiudolls
9.8 �C70.4 cm
NJ/Rutgers Univ.
40.4631173 N
2008 Nixon loam and Sassafras-Urban
sandy loam complex
(Ultisols/Alfisols)
Fine-loamy, siliceous, semiactive,
mesic Typic Hapludults þFine -loamy, mixed, active, mesic
Aquic Fragiudalfs
11.4 �C123.9 cm
IL/Havana
40.2960410 N
2004 Disco sandy loam (Mollisols) Coarse-loamy, mixed, superactive,
mesic Pachic Hapludolls
10.8 �C96.0 cm
IL/Urbana
40.0425649 N
2002 Flanagan silt loam (Mollisols) Fine, smectitic, mesic Aquic Argiudoll 10.8 �C104.3 cm
IL/Orr
39.806104 N
2004 Winfield silt loam (Alfisols) Fine silty, mixed, superactive,
mesic Oxyaquic Hapludalf
10.8 �C97.7 cm
IL/Pana
39.443383 N
2004 Virden silty clay loam (Mollisols) Fine, smectitic, mesic Vertic
Argiaquolls
11.4 �C103.0 cm
IL/Brownstown
38.9500000 N
2004 Hoyleton silt loam (Alfisols) Fine, smectitic, mesic Aquollic
Hapludalfs
11.6 �C106.8 cm
IL/Fairfield
38.3810019 N
2004 Wynoose silt loam (Alfisols) Fine, smectitic, mesic Typic
Albaqualfs
12.2 �C114.3 cm
KY/Univ. of Kentucky
38.1277798 N
2008 Bluegrass-Maury silt loams
(Alfisols)
Fine silty, mixed, active, mesic
Typic Paleudalf þ Fine, mixed,
active, mesic Typic Paleudalf
12.9 �C116.6 cm
IL/Dixon Springs
37.4535770 N
2002 Grantsburg silt loam (Alfisols) Fine silty, mixed, Active, mesic
Oxyaquic Fragiudalf
14.5 �C122.5 cm
OK/Oklahoma State Univ.
35.991500 N
2009 Teller fine sandy loam (Mollisols) Fine-loamy, mixed, active, thermic
Udic Argiustolls
15.2 �C93.2 cm
MS/Mississippi State Univ.
33.424608 N
2009 Marietta fine sandy loam
(close to Ultisols)
Fine-loamy, siliceous, active, thermic
Fluvaquentic Eutrudept
16.8 �C140.8 cm
b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 3 2809
overnight with the door closed. Two grams of sodium
hydroxide (NaOH) were added to each ashed sample and
immediately heated with a Bunsen burner for 15min to create
a soluble sodium cake. Samples were swirled after first 5 min
of heating for proper mixing of the sample and NaOH. After
letting them cool for about 30min, deionized water was added
up to one-third of the crucible’s volume and let to stand
overnight. The solution of sodium silicate cake was then
transferred to 100 mL volumetric flasks, approximately 50 mL
of deionized water was added and 2 mL of H2SO4 solution was
added using a repeating pipette. After bringing up to the total
volume of 100 mL with deionized water and mixing well, total
Si concentrations (mg L�1) were analyzed on a Lachat Quik-
Chem 8000 flow injection analyzer (Lachat Instruments/Hach
Company, Loveland, CO) at 820 nm absorbance with
a minimum detection limit of 0.15 mg SiO2 L�1. A quality
control check standard (QCCS), representing the approximate
midpoint of the calibration range was included as the first
sample in each set and was repeated following every eighth
sample. All QCCS value determinations were within 10% of
the actual concentration. Each plant tissue sample was
analyzed in duplicate. Three blanks and three samples of San
Joaquin Soil (10 mg) of known value (29.66% Si) as standard
reference materials (U.S. Department of Commerce, National
Institution of Standard and Technology (NIST), Gaithersburg,
MD, U.S.A) were included in each batch of plant samples.
There are no plant reference materials with known Si
concentrations available, and the standard soil was the only
known standardwe could locate. However, we did utilize NIST
pine needle reference material as well, using it as a consis-
tency check from batch to batch, as there is no known Si
concentration given. Volumetrics of 500 mL were used for
standard soil samples to achieve a desired dilution. Analytical
duplicate and spiked samples were also prepared for every
seventh sample in each run to ensure accuracy and a precise
determination. Each of the concentrations of measured Si in
plant samples were adjusted based on the known values for
the standard San Joaquin soil reference material versus the
measured value in each batch, and in some cases with the
pine needle concentration.Most correctionswere<10%, but in
some batches the standard soil or pine needle had consistent
values within the batch, but different than either the known
soil or our established pine needle concentration, leading to
larger corrections. When the difference between duplicate
plant samples and triplicate soil standards exceeded 10% of
the concentration with each other, those samples were
reanalyzed. Calculation of descriptive statistics, two-sample t-
test, and regression analyses were performed in SAS using the
univariate (PROC UNIVARIATE), t-test (PROC TTEST), and
multiple regression (PROC GLM) procedures [30], respectively.
Table 3 e Silicon concentrations in switchgrass plantsamples collected from various trial plots in Illinois.
State/Location
Mean % � sd(n ¼ 4)
Median%
Maximum%
Minimum%
IL/Dekalb 1.58 � 0.21 1.61 1.76 1.33
IL/Havana 1.10 � 0.39 1.04 1.62 0.71
IL/Urbana 1.53 � 0.35 1.43 2.03 1.23
IL/Orr 1.26 � 0.42 1.20 1.74 0.73
IL/Pana 1.49 � 1.49 1.64 1.70 0.99
IL/Brownstown 2.38 � 0.57 2.39 2.94 1.79
IL/Fairfield 1.53 � 0.55 1.43 2.28 0.98
IL/Dixon
Springs
2.18 � 0.40 2.23 2.53 1.71
Overall 1.63 � 0.43 1.53 2.38 1.10
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3. Results
Silicon concentrations in M. � giganteus plant samples from
across the eastern U.S. ranged from 0.72% to 1.62%. (Table 2).
Among all values, the range of average Si concentrations was
greater for the eight sites in Illinois (0.55%e2.42%). Both the
lowest and highest limits of Si concentrations were thus
observed among trial plots of Illinois. Out of four replicates,
one each in Dekalb and Dixon Springs had very high concen-
trations (3.19% and 4.28%, respectively); exceeding the
maximum value obtained among rest of the samples (data not
shown). The overall mean value of Si concentrations in
M. � giganteus samples among all sites was 1.16% and the
overall median value was 1.08%.
Among the ‘Cave-in-Rock’ switchgrass biomass samples
collected from eight different trial plots in Illinois, the average
concentrations ranged from 1.10% to 2.38% (Table 3). The
upper limit was similar to that of M. � giganteus samples
whereas the lower level was about two-fold greater. Themean
Si concentration in M. � giganteus samples was significantly
lower (P < 0.01) than that in switchgrass (1.63%) and the
overall median value inM. � giganteus samples (1.08%) was 1.4
times lower than that for ‘Cave-in-Rock’ switchgrass (1.53%).
The result of six other types of Miscanthus spp. samples
from the Urbana trial plot in Illinois showed that Si concen-
trations were also highly variable (Table 4), ranging from
0.81% to as high as 3.56%. Themedian value was 2.78%, which
is about three times higher than that for M. � giganteus
samples.
Table 2 e Silicon concentrations in Miscanthus plantsamples from biomass trial plots.
State/Location
Mean% � sd(n ¼ 4)
Median%
Maximum%
Minimum%
MI/MSU Kellogg
Biological
Station
0.72 � 0.11 0.75 0.80 0.56
IL/Dekalb 1.59 � 0.96 1.25 3.19 0.66
NE/Univ. of
Nebraska
0.69 � 0.13 0.68 0.91 0.57
NJ/Rutgers
Univ.
0.88 � 0.13 0.96 0.96 0.73
IL/Havana 0.55 � 0.18 0.54 0.77 0.36
IL/Urbana 1.19 � 0.45 1.26 1.57 0.66
IL/Orr 0.79 � 0.25 0.81 1.00 0.53
IL/Pana 0.80 � 0.27 0.82 1.09 0.47
IL/Brownstown 0.99 � 0.26 0.90 1.43 0.79
IL/Fairfield 1.59 � 0.51 1.59 2.30 1.00
KY/Univ. of
Kentucky
1.62 � 0.33 1.74 1.87 1.14
IL/Dixon
Springs
2.42 � 1.30 1.96 4.28 1.50
OK/Oklahoma
State Univ.
1.20 � 0.08 1.20 1.30 1.08
MS/Mississippi
State Univ.
1.17 � 0.09 1.19 1.25 1.05
Overall 1.16 � 0.51 1.08 2.42 0.55
Multiple regression models were used to evaluate the
genotypeeenvironment interactions among M. � giganteus
and ‘Cave-in-Rock’ switchgrass samples and various factors
such as plant age, soil type, fertility, latitude, and mean
annual temperature and precipitation. The results showed
that there was no significant relationship between any of
these factors and Si concentrations (data not shown).
However, there was a strong tendency of higher Si concentra-
tions in the locationswith low latitude and greater temperature
and precipitation. This tendency was common both for
M. � giganteus and ‘Cave-in-Rock’ switchgrass samples. When
two remarkably higher values of Si concentration in
M. � giganteus samples were excluded, the correlation between
Si concentrations and temperature and precipitation became
significant at 5% level of significance (Fig. 1).
4. Discussion
High variability in mineral concentrations among promising
biofuel crops can be considerable as it depends on genetic and
environmental factors [31] as well as physiological and
morphological difference among crops [14,20]. In this study,
average percentage of Si concentrations in M. � giganteus
plant biomass samples varied widely among the locations.
Previous studies also reported high variability, ranging from
0.46e2.11% [32,33,34]. Another species of Miscanthus (i.e. Mis-
canthus sacchariflorus), had the reported values ranging from
0.55% to 1.42% [32,33,35], but our sample had a much higher
concentration (3.24%). Among the several cultivars of
Table 4 e Silicon concentrations in different genotypes ofMiscanthus plant samples collected from Urbana trialplots in Illinois.
Species Silicon (%)(n ¼ 1)
M. sacchariflorus 3.24
M. sinensis ‘Siberfeder’ 1.69
M. sinensis ‘Graziella’ 0.81
M. sinensis ‘Rigoletto’ 2.75
M. sinensis ‘Zebrinus’ 3.56
M. sinensis ‘Bluetenwunder’ 2.82
Mean annual temperature (°C)8 10 12 14 16 18
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Mean annual precipitation (cm)60 80 100 120 140 160
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
)%(
noitartnecnociSy = 0.0122x - 0.2092R2 = 0.31, p < 0.037
y = 0.0926x - 0.0228R2 = 0.32, p < 0.036
a
b
Fig. 1 e Relationship between Miscanthus Si concentrations
at each site and (a) mean annual temperature and (b) mean
annual precipitation.
Table 5 e Silicon concentrations in different species ofMiscanthus and switchgrass in this study and literatures.
Species Silicon (%) Reference
Miscanthus � giganteus 0.62e1.21 [32]
1.42e2.11 [33]
0.46e0.96 [34]
0.55e2.42 This study
(median value ¼ 1.08)
Miscanthus sacchariflorus 1.42 [35]
0.55e0.96 [32]
0.86e0.96 [33]
3.24 This study
Miscanthus sinensis 2.86 [36]
3.20 [35]
0.45e1.67 [20]
0.78e0.86 [32]
1.05e1.33 [33]
M. sinensis ‘Siberfeder’ 1.69 This study
M. sinensis ‘Graziella’ 0.81 This study
M. sinensis ‘Rigoletto’ 2.75 This study
M. sinensis ‘Zebrinus’ 3.56 This study
M. sinensis ‘Bluetenwunder 2.82 This study
Panicum virgatum 0.53e1.57 [20]
2.01 [23]
0.38e1.40 [37]
0.18e2.86 [38]
1.03e5.04 [39]
1.10e2.38 This study
b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 3 2811
Miscanthus sinensis measured in this study, the concentration
ranged from 0.81% to 3.56% (Table 5), which was similar to the
reported values, ranging from 0.45% to 3.20% [20,32,33,35,36].
‘Cave-in-Rock’ switchgrass also showed a high variability
in Si concentration ranging from 1.10% to 2.38% but the vari-
ability was lower compared to that for Miscanthus spp. A
similar range of Si concentration was reported by Monti et al.
[20], Hodson et al. [36], and El-Nashaar et al. [37] (Table 5). El-
Nashaar et al. [38] studied various elements such as Si, chlo-
rine, sulfur, phosphorus, and potassium in native temperate
grasses grown in thewesternU.S. and reported a greater range
of Si concentrations in switchgrass (0.18e2.86%). Even higher
values were reported by Lanning and Eleuterius [39] ranging
from 1.03% to 5.04% in various parts of switchgrass plants.
Among the studied biofuel feedstock crops switchgrass and
different genotypes of Miscanthus, M. � giganteus grown in
research trial plots of different states had the lowest Si
concentrations (median value 1.08%). This result favors the
suitability of this crop for producing biofuel with efficient
combustion process because lower Si concentration enhances
better thermochemical conversion [18]. Comparing the
combustion quality among coal, straw, wood, cereal, andM.�giganteus, Lewandowski and Kicherer [2] reported that
M. � giganteus biomass had very good combustion quality due
to its low water concentration as well as its low chlorine,
potassium, nitrogen, sulfur, and ash concentrations. It
appeared that M. � giganteus could be a promising biofuel
feedstock crop in the U.S. given its reduced level of Si
concentration together with its superiority in nitrogen and
water use efficiency, good pest and disease resistance [11,12],
and high yield potential [10].
There is not enough known about the contributing factors
to Si concentrations in these biofuel feedstock crops. Visser
and Pignatelli [34] attributed variability in Si concentration
in plant biomass to difference in harvesting methods or in
soil types. Our study did not exhibit apparent relationships
between soil types and Si concentrations in plant biomass. A
previous study also reported that variations in mineral
concentrations including Si in plant biomass samples were
not related to soil chemistry [38]. In a study conducted for
different genotypes of switchgrass in five locations in the U.S.,
El-Nashaar et al. [37] reported that location had a strong
impact on mineral concentrations including Si and latitude of
origin impacted the Cl and Si concentrations in plant tissues.
They reported that the least Si occurred in plants grown at the
two coolest locations of Wisconsin, whereas the greatest Si
concentrations were observed in plants grown in Kansas with
warm mid-summer temperature. Our findings also indicated
that warmer locations with relatively higher precipitation
amount had a tendency of greater Si concentration in both
M. � giganteus and ‘Cave-in-Rock’ switchgrass samples. There
could be a strong influence of location on the biomass quality
due to the influences on the development of the plant, and due
to precipitation, which causes the leaching of minerals [2]. At
locations with temperate climates, soil freezing and thawing
cycles in winter could have potential impact on weathering
b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 8 0 7e2 8 1 32812
and leaching of soil minerals that could influence mineral
uptake by plants, resulting in greatermineral concentration in
plant biomass. Studies of Si accumulation during heat adap-
tation suggest that warmer temperatures are accompanied by
an increased formation of Si bodies and increased Si-con-
taining leaf pubescence in grasses [40].
5. Conclusions
Among the plant biomass samples of M. � giganteus collected
from six different eastern U.S. states and eight trial plots in
Illinois, ‘Cave-in-Rock’ switchgrass from eight plots in Illinois,
and six different genotypes of Miscanthus in Urbana, M. �giganteus had the lowest level of Si concentrations in plant
tissues, indicating its greater potential with respect to biofuel
quality. Locations with warmer temperature and greater
precipitation generally had higher Si concentrations in plant
biomass. Further research to assess the long-term impact of
soil Si concentrations in different locations and other possible
environmental factors such as magnitude of leaching associ-
ated with duration of snow-cover and freezing-thawing
processes might be of importance and help understand
M. � giganteus, one of the most promising biofuel crops.
Acknowledgments
Funding was provided by the State of Illinois through the
Illinois Council on Food and Agricultural Research (C-FAR),
Biomass Energy Crops Strategic Research Initiative and by
the Energy Biosciences Institute. We thank cooperators for
providing biomass samples.
r e f e r e n c e s
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