Yudai Sumiyoshi , Susan E. Crow Time (month) · 2015-06-03 · 9 9 9 10 10 Mar 10 Apr 10 10 10 ul 10 Aug 10 Sep 10 10 10 10 11 11 Mar 11 Apr 11 11 11 ul 11 ce CO 2 Flux (g C in CO
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Oct 9Nov 9
Dec 9Jan 10
Feb 10Mar 10
Apr 10May 10
Jun 10Jul 10
Aug 10Sep 10
Oct 10Nov 10
Dec 10Jan 11
Feb 11Mar 11
Apr 11May 11
Jun 11Jul 11S
oil
Su
rfa
ce
CO
2 F
lux (
g C
in C
O2
m-2
da
y-1
)
0
2
4
6
8
Guinea
Napier
CB
CG
Oct 9Nov 9Dec 9Jan 10Feb 10Mar 10Apr 10May 10Jun 10Jul 10Aug 10Sep 10Oct 10Nov 10Dec 10Jan 11Feb 11Mar 11Apr 11May 11Jun 11Jul 11
So
il te
mp
(C
)
20
22
24
26
28
30
32
So
il M
ois
ture
(%
v/v
)
0.25
0.30
0.35
0.40
0.45
0.50
0.55
OG03OG05
K06MG04
Local
PurplePxD
254 CB CGCum
ula
tive
So
il C
O2 F
lux (
g C
in
CO
2 m
-2)
0
1000
2000
3000
0.2250.2000.1750.1500.1250.1000.0750.050
4400
4200
4000
3800
3600
3400
3200
3000
Root Decay Constant
So
il C
in
EM
S 0
.2 t
m-2
(g
m-2
) Guinea
Napier
0.2250.2000.1750.1500.1250.1000.0750.050
4200
4100
4000
3900
3800
3700
3600
3500
3400
Root Decay Constant
So
il C
in
EM
S 0
.2 t
m-2
(g
m-2
) Guinea
Napier
OG03OG05
K06MG04
Local
PurplePxD 254 CB CG
Root B
iom
ass C
(g m
-2)
0
50
100
150
200
250
300 2010
2011
OG03OG05 K06
MG04Local
Purple PxD 254 CB CG
Changes in S
oil
C S
tock (
%)
-15
-10
-5
0
5
10
15
OG03OG05
K06MG4
Local
PurplePxD
254 CB CG
So
il C
in
EM
S 0
.2 t
m-2
(g
m-2
)
0
1000
2000
3000
4000
5000
6000
2010
2011
Guinea Napier
Roo
t D
ecay c
on
sta
nt
0.00
0.05
0.10
0.15
0.20
OG03 OG05 K06 MG04 Local Purple PxD 254
Roo
t D
ecay C
onsta
nt
0.00
0.05
0.10
0.15
0.20
0.25
Belowground Carbon Cycle of Napier and Guinea Grasses Yudai Sumiyoshi1, Susan E. Crow1, Creighton M. Litton1, Jonathan L. Deenik2
1. Department of Natural Resources and Environmental Management, 2. Department of Tropical Plant and Soil Sciences,
University of Hawaiʻi at Mānoa, Honolulu, HI, United States.
Results Discussion Introduction
Objectives and Hypotheses
Materials and Methods
Conclusion
Acknowledgements References
• Gifford, R. M., & Roderick, M. L. (2003). Soil carbon stocks and bulk density: spatial or cumulative mass coordinates
as a basis of expression? Global Change Biology, 9(11), 1507-1514.
• Golchin, A., Oades, J., Skjemstad, J., & Clarke, P. (1994). Study of free and occluded particulate organic matter in
soils by solid state 13C Cp/MAS NMR spectroscopy and scanning electron microscopy. Australian Journal of Soil
Research, 32(2), 285-309.
• Raich, J. W., Russell, A. E., & Valverde-Barrantes, O. (2009). Fine root decay rates vary widely among lowland
tropical tree species. Oecologia, 161(2), 325-330.
Many thanks to Dr. Creighton M. Litton for Li-6400 portable photosynthesis system, Ray Uchida for Cyclone Micromill,
and Dr. Rebecca Ostertag for advises on litterbag decay study. Also thanks to Mataia Reeves, Meghan Pawlowsky, Heather
Kikkawa, Anne Quidez, John Wells, Mariko Panzella and Alisa Davis who helped me in various tasks in lab and field.
Finally thanks to entire bioenergy feedstock team and especially Guy Porter and Roger Corrales (Field manager,
Waimanalo Research Station) for the maintenance of the field. This collaborative study was made possible by funding
provided by the US Department of Energy (DE-FG36-08G088037 awarded to A. Hashimoto, CTAHR University of
Hawaii Manoa).
For additional information, contact Yudai Sumiyoshi:
1910 East West Road Sherman lab 101 Honolulu, Hawaii 96822
E-mail: yudais@hawaii.edu Phone: (808)956-5435
• Napier grass (Pennisetum purpureum) and Guinea grass
(Urochloa maxima) are perennial C4 grasses with high
capacity to produce large amounts of both aboveground and
belowground biomass.
• Additional carbon (C) stored in soil can offset the CO2
emissions associated with growing feedstock and producing
bioenergy (Fig. 1).
• In this study, both grasses were ratooned (no-till) to leave belowground biomass intact and
facilitate C accumulation through improvement of soil aggregation.
• To date, no information on belowground C cycle for Guinea and Napier grasses is available.
• An accurate assessment of C sequestration potential is needed for grass accession selection
and environmental benefit assessment of the bioenergy system as a whole.
Objectives
1. Measure the quantity and quality of belowground C input.
2. Observe and explain the differences between accessions and species.
3. Determine how these two factors affect changes in soil C pools.
Hypotheses
• H1: Roots with recalcitrant characteristics will result in a slower decomposition rate than one
with a more labile nature.
• H2: Grass accessions with higher quantity of belowground carbon input results in higher
amount of C stored in soil.
• H3: Grass accessions with recalcitrant belowground biomass characteristics result in higher
amount of C stored in the soil.
Litter Decay Area
CG4
CG2CG3
Control Grass (CG) 1
CB4
CB3
CB2
CBare 1
Variety Trial Plot
Environment
• Waimanalo, Oahu, Hawaii (21°20’15” N, 157°43’ 30” W).
• Soil: Very-fine, mixed, superactive, isohyperthermic Pachic Haplustolls
• Randomized complete block of 2 m by 3 m plots with 4 reps.
• 8 accessions were chosen as accessions of interest.
• Guinea: OG03, OG05, K06, MG4
• Napier: Local, Purple, PxD, 254
• Planted on Oct 2009, ratooned on March, Nov 2010, and July 2011.
• Two controls: 4 plots each in tilled bare (Control Bare: CB) and fallow no
tilled areas (Control Grass: CG) (Fi. 2).
Belowground Input Quantity
Soil CO2 Flux:
• Measured monthly with Li6400 Portable Photosynthesis system (5 collars
per plot) (Fig. 4).
• Annualized Soil CO2 flux by and converted to g C in CO2 m-2 yr-1.
Root Biomass C:
• Measured on April 2010 and Aug 2011.
• Roots were collected on 0.5 mm sieve after dispersing soil core with 10 %
sodium hexametaphosphate solution.
• Root C concentrations were analyzed with elemental analyzer (EA).
Belowground Input Quality
• Analyzed for root lignin concentration by Van Soest Method and nitrogen
(N) concentration by EA.
• Roots (0.5 g ) buried in 5 cm by 5 cm, 132 micron mesh nylon bag (Fig. 4).
• Bags harvested on 1, 2, 3, 5, and 8 months after deployment.
• Root C remaining (%) over time plotted to determine “k” = decay constants
(Fig. 5).
• Higher decay constant => Faster decay
Soil Carbon Stock
• Measured from soil core (5 cm diameter, 2 per plot) collected in 0-30 cm
on April 2010 and August 2011.
• Used equivalent mass of soil (EMS) method (Gifford & Roderick, 2003).
• ∆ soil C = soil C stock at Aug 2011 – soil C stock at April 2010
• % change = ∆ soil carbon / soil C stock at April 2010 x 100
0 4 8 12 162Meters
Figure 4. Litterbag filled with root tissue
Figure 3. Li 6400 portable photosynthesis system
with soil respiration chamber.
I. Belowground Input Quantity
II. Belowground Input Quality
ARN: 1182028 PN: B11A-0469
I. Belowground Input Quantity
• Root biomass C more suited differentiator of accessions than cumulative
soil CO2 flux.
• No association between root biomass C and cumulative CO2 flux.
• Higher root biomass C but similar soil CO2 flux suggest that C input is
going to soil C instead of getting lost as CO2.
II. Belowground Input Quality
• Although no significant differences between accessions in decay
constant, there are some variability.
• Relationship between lignin to decay constant agrees with previous
literature (eg. Raich, Russell, & Valverde-Barrantes, 2009).
III. Soil C Stock
• Significant increase (p<0.05) in soil C from 2010 for Napier accessions
while none of Guinea accessions had significant increase.
• Significant decrease in CB (p<0.1) due to no inputs of C.
• None of quantity factors alone explained differences in soil C stocks or
change in two sampling dates.
• Grass accessions with greater root decay constants were associated with
greater soil C stocks.
H1. Roots with higher lignin to N ratio tend to decay slower compared to
ones with lower lignin to N ratio.
H2. Belowground input quantity factor themselves showed no effect on soil
C accumulation.
H3. Belowground input quality had effect on soil C where grass accessions
with easier to decay roots tend to have higher soil C than ones with more
recalcitrant roots.
C loss from root through decay = C gain in soil C stock, not C loss
through respiration.
Even though the study was conducted in short term, soil C stock increased
significantly in Napier accessions. In long term, management of continued
ratooning (no-till) of those grasses may realize in significant differences in
soil C stock compared to other land management practices.
Thus, long term study is needed to fully understand mechanisms of
changes in soil C due to Napier and Guinea grasses.
• Significant differences between two Napier accessions (Local
and 254) and bare soil (CB) (Fig. 7).
• No significant differences observed between accessions (Fig. 7).
• Significant increase in root biomass C in 0-30 cm depth from
April 2010 to August 2011 (Fig 8).
• Local (Napier) had significantly higher root biomass C than K06
and MG04 (both Guinea) in 2011 (Fig. 8).
• Significant difference in root biomass C was not associated with
cumulative soil CO2 flux (data not shown).
Fig. 12. Comparison of averaged root decay constant for two species
Fig. 10. Root decay constants of accessions
• Only Feb 2011 had significant difference in soil
CO2 flux rates for accessions (data not shown).
• No significant differences in monthly soil CO2
flux rates for species (Fig. 6).
• Flux rates increased after 2nd harvest due to
fertilization (Fig. 6).
ANOVA (p=0.007: r2 (adj) = 34.97%)
Tukey separation (error = 0.5)
ab ab ab ab
a
ab ab
a
b ab
Fig. 7. Cumulative soil CO2 flux from Aug 2010 to 2011 Figure 8. Root biomass in initial soil samples.
Figure 6. Monthly soil CO2 flux rates for two species averaged and controls
2nd ratoon
+ fertilization
1st ratoon
+ soil sampling
Fig. 9. Root C remaining over time in 8 month decay for accessions
Fig. 11. Root C remaining over time in 8 month decay for two species
No significant differences
ANOVA p=0.098
r2 (adj) = 19.37%
a
b
Fig. 13. Scatterplot of root initial lignin to N ratio against decay constant
• No significant differences in root C remaining
and root decay constants between accessions
(Fig. 9-10).
• Guinea accessions significantly higher root C
remaining for species over months of decay
(Fig. 11) and root decay constant (Fig. 12).
• Significant relationship between root initial
lignin to N ratio and root decay constant (Fig.
13).
Fig. 14. Soil C stocks in April 2010 and August 2011 Fig. 15. Changes in soil C stock for accessions and controls
Fig. 17. Scatterplot of root decay constant against soil C stock in 2011
Fig. 16. Scatterplot of root decay constant against soil C stock in 2010
• No significant differences in soil C stocks for accessions for both year (Fig. 14).
• Significant increase in soil C stock from 2010 observed in Napier accessions and CB
indicated by arrows (blue = p<0.05 and red = p<0.1) (Fig. 15).
• No relationship observed between cumulative soil CO2 flux, root biomass C, or root lignin
to N ratio against soil C stocks, ∆ soil C, or % changes in soil C stock.
• Root decay constant had significant relationship with soil C stocks in both April 2010 and
August 2011 (Fig. 16-17).
• Relationship became stronger in August 2011 (Fig. 17).
Fig. 2. Map of study site in Oahu, Hawaii
Fig. 1. Biofuel life cycle with associated energy inputs
2 mm sieved soil
Fig. 18. Three fractions of soil C by Golchin Method
3rd ratoon
+ Soil Sampling
Accession Trial Plots
Figure 5. Decay constant equation based on decay curve.
II. Soil C Stock
Next Step: Soil Fractionation
• Soil C pools may have shifted differently
than bulk soil C.
• Soil C will be fractionated into 3 different C
pools using the Golchin method (Golchin et
al., 1994) (Fig. 18).
Hypotheses
• Variability in bulk soil C stock is due to
difference in light C.
• Accession with higher decay constant
accumulate more C in light fraction.
Time (month)
0 1 2 3 4 5 6 7 8 9
Root C
Rem
ain
ing (
%)
0
20
40
60
80
100
OG03
OG05
K06
MG4
Local
Purple
P x D
254
Time (month)
0 1 2 3 4 5 6 7 8 9
C in R
oot R
em
ain
ing (
%)
0
20
40
60
80
100
Guinea
Napier Significant difference (p=0.004)
p=0.03
p=0.034 p=0.001
p=0.007
Eg. y = 100e-0.127x R² = 0.9743
0
20
40
60
80
100
120
0 2 4 6 8 10
Ro
ot
C r
emai
nin
g (%
)
Time (month)
Mt = M0 e -kt
p=0.0005
r2 (adj) = 33.3%
p=0.032
r2 (adj) = 12.0%
p=0.004
r2 (adj) = 23.0%
Planting
+ fertilization
a
b b
b b
2011
ANOVA (P=0.001: r2 (adj) = 45.1 %)
Tukey separation (error = 0.5)
No significant differences for
both year
No significant differences
in root C remaining
ab ab ab ab
ab
2010
2011
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