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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oil

Su

rfa

ce

CO

2 F

lux (

g C

in C

O2

m-2

da

y-1

)

0

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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

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32

So

il M

ois

ture

(%

v/v

)

0.25

0.30

0.35

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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

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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: [email protected] 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