No. 56 Improvement of Terrestrial Ecosystem Model in terms of High CO2 ResponseAkihiko Ito *, Atsuhiro Iio, Minaco Adachi, Masako Senda, Tomohiro Hajima, Koki Hikosaka, Ichiro Terashima

* Correspondence: National Institute for Environmental Studies, Japan; Japan Agency for Marine-Earth Science and Technology; e-mail: itoh@nies.go.jp

45

50

55

60

65

70

75

0.8

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

1900 1920 1940 1960 1980 2000

NPP

AET

WUE

Year

NP

P (P

g C

/ yr

) or A

ET

(10

3 km

3 /

yr)

WU

E (g

C /

kg w

ater

)

0 100 200 300 400 500 600

-80

-60

-40

-20

0

20

40

60

80

Fekete et al. 2002 (WBM)Fekete et al. 2002 (CMP)

VISIT (this study)

0 100 200 300 400 500 600

-80

-60

-40

-20

0

20

40

60

80

Cramer et al. 1999VISIT (this study)

(a) Runoff

(km3 / yr) (Tg C / yr)

(b) NPP

La

titu

de

(d

eg

ree

)

canopy

actual evapotranspiration (AET)[65.0]

precipitation[107.2]

photosynthesis[124.6]

net primary production (NPP)[59.5]

water-use efficiency (WUE)[ 0.915 g-carbon / kg-water ]

ecosystemrespiration

auto

rtoph

ic

trans

pi-

ratio

n

evap

orat

ion

inte

rcep

tion

hete

rotro

phic

leaf-stomata

leaf area

runoff [42.2]

water erosion [1.2]

plantbiomass[519.7]

stocks (flows)[Pg C (/ yr)]

stocks (flows)[103 km3 (/ yr)]

soilorganicmatter

[1289.6]

soilmoisture

(root uptake)

(sap flow)

(litterfall)

fire, BVOC, CH4, etc.

(a)

(b)

0°

60°

90°

30°

-30°

-60°

0°

60°

90°

30°

-30°

-60°0° 60°-60° 120°-120° 180°-180°

0° 60°-60° 120°-120° 180°-180°

AET(kg m–2 yr–1)

NPP(kg C m–2 yr–1)

0

1000

800

600

400

200

0

1.0

0.8

0.6

0.4

0.2

(a)

(b)

0°

60°

90°

30°

-30°

-60°

0°

60°

90°

30°

-30°

-60°0° 60°-60° 120°-120° 180°-180°

0° 60°-60° 120°-120° 180°-180°

WUES(g C kg–1)

0.0

2.0

1.5

1.0

0.5

WUEL(g C kg–1)

0

45

40

35

30

25

20

15

10

5

PhotosynthesisPEPPs model

RespirationPEPPs model

AllocationPEPPs model

N absorptionPEPPs model

CO2

Leaf areaReproduction

C/N balance

Plant hormone

Signal transfer

Consortium target

CO2NET study(CO2 response information transfer network )

Acclimation

Soil N

Stomata PEPPsmodel

Model plantsFACE/OTC

・ High CO2 exp.・ N-level manipulat.• Omics analysis• PEPPs obs.・ Leaf gas exchange・ Growth analysis• Isotope tracer・ etc.

-300

-200

-100

0

100

200

Disturbance

Elevated CO2

Temperature

Precipitation

Radiation

Non-linearity

GPPRENEP

Car

bon

budg

et, 1

994–

2009

(g C

m –

2 yr

–1 )

Sca

ling

coef

fici

ents

(–)

-2

-1

0

1

2

3

Disturbance

Elevated CO2

Temperature

Precipitation

Radiation

GPPRENEP

-50

0

50

100

150

200

250

300

350

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

-50

0

50

100

150

200

250

300

350

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

-50

0

50

100

150

200

250

300

350

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

Year

Obs.VISIT (control)

(a) GPP

(b) RE

(c) NEP

CO

2 flu

x (g

C m

–2

mon

th –

1 )

Leaf Stem Root

Leaf Stem Root

Dead leaf Dead stem Dead root

Active Intermediate Passive

talltrees

litter

humus

floorplants

Atmospheric CO2

allocation

photosynthesis respiration

decomposition min

eral

izat

ion

litter fallallocation

FGPP

GPP – AR – HR = –NEENEP

Auto. Resp.

Eco. Resp.

Hetero. Resp.

Soil Resp.

=

Comprehensive studies of plant responses to high CO2 world by an innovative consortium of ecologists and molecular biologists

Model development : VISIT

Study 1:Detection and attribution of global change and disturbance impacts on a tower-observed ecosystem carbon budget: a critical appraisal

Study 2 : Water-use efficiency of the terrestrial biosphere: a model analysis focusing on interactions between the global carbon and water cycles

Observations worldwide are providing an increasing amount of atmosphere–ecosystem flux

data. Thus, establishing a data-mining methodology to detect significant trends and attribute

changes to specific factors is important. This study examined the possibility of detecting

significant trends in observed data at a test site with one of the longest records of flux

measurements (Takayama, Japan). Statistical tests using non-parametric methods showed

a ‘likely’ trend (i.e., detected at 66–90% confidence levels) of increasing carbon

sequestration. To investigate the change in carbon sequestration in relation to biological

and environmental factors (ambient CO2, temperature, radiation, precipitation, and

disturbance), mechanistic and numerical methods were applied. A process-based model

was used for the mechanistic attribution of change, and an optimal fingerprinting method in

combination with model-based sensitivity simulations for numerical attribution. At the study

site, local disturbances appeared to exert an impact on the observed carbon sequestration,

whereas climatic factors made moderate contributions. These results indicate the feasibility

of detection and attribution using current flux measurement data, although more evidence is

needed to confirm global coherence.

Carbon and water cycles are intimately coupled in terrestrial ecosystems, and

water-use efficiency (WUE, carbon gain at the expense of unit water loss) is

one of the key parameters of ecohydrology and ecosystem management. In this

study, the carbon cycle and water budget of terrestrial ecosystems were

simulated using a process-based ecosystem model, called Vegetation

Integrative SImulator for Trace gases (VISIT), and WUE was evaluated: WUEC

defined as gross primary production (GPP) divided by transpiration, and WUES

defined as net primary production (NPP) divided by actual evapotranspiration.

Total annual WUEC and WUES of the terrestrial biosphere were estimated as

8.0 and 0.92 g C kg–1 H2O, respectively, for the period 1995–2004. Spatially,

WUEC and WUES were only weakly correlated. WUES ranged from <0.2 g C

kg–1 H2O in arid ecosystems to >1.5 g C kg–1 H2O in boreal and alpine

ecosystems. The historical simulation implied that biospheric WUE increased

from 1901 to 2005 (WUEC, +7% and WUES, +12%) mainly as a result of the

augmentation of productivity in parallel with the atmospheric carbon dioxide

increase. Country-based analyses indicated that total NPP is largely determined

by water availability, and human appropriation of NPP is also related to water

resources to a considerable extent. These results have implications for (1)

responses of the carbon cycle to the anticipated global hydrological changes;

(2) responses of the water budget to changes in the terrestrial carbon cycle; and

(3) ecosystem management based on optimized resource use.

ReferencesIto A (2012) Detection and attribution of global change impact on a

tower-observed ecosystem carbon budget: a critical appraisal. Environmental Research Letters, 7, 1–6.

Ito A, Inatomi M (2012) Water-use efficiency of the terrestrial biosphere: a model analysis on interactions between the global carbon and water cycles. Journal of Hydrometeorology, 13, 681–694.

Scales

Targets

Mutant / transgenic p

lant

Omics

Inter-specifi

c compariso

n

Model parameterization

Simulation / validation

Molecule / cell

Individual / o

rgan

Ecosystem

Earth

Molecular biology

Ecophysiology

Simulation study

This project explores “inclusive elucidation of plant

response to elevated atmospheric CO2

concentration” , i.e., an urgent issue to establish a

basis to make prediction of the plant CO2 fixation in

response to global environmental change, through the

formation of a consortium of ecologists and molecular

physiologists. First, we raise plants under high CO2

conditions and analyze the dynamics of information

network concerning environmental response by

means of targeted omics, allowing us to grasp the

whole features of plant CO2 response. Then, we

specify analytical factors and apply them to

representative species of natural ecosystems

including tree species, in order to clarify the plant high

CO2 response with respect to environmental

dependence and inter-species differences in a

quantitative and inclusive manner. Based on these

findings, we develop a molecular physiological model

of individual plant high CO2 response, which will be

provided to ecosystem model researchers. Finally, we

break a new direction of molecular physiology to

make effective contribution to plant individual-level

studies and to make substantial progress in botanical

science.

To achieve these purposes, we analyze

phenotypic ecophysiological parameters (PEPPs)

such as stomatal conductance, photosynthetic rate,

respiration rate, C/N balance, allocation (aboveground

/ belowground, leaf / stem and branching), and

growth, which are usually used in ecophysiological

studies, by means of indoor remote sensing,

high-definition gas exchange measurement, stable

isotopic tracer experiment, and other methods,

utilizing previously-identified mutant plants that have

functional loss and gain in CO2 response factors. In

parallel with the PEPPs responses, we elucidate the

whole features of plant CO2 response by

understanding the dynamics of CO2 response

information-transfer network (CO2NET) through

targeted omics for plant metabolites and hormones.

We establish and maintain a platform to measure the

group of marker factors such as genes, enzymes,

metabolites, and hormones, which play key roles in

the CO2NET.

This study used the process-based terrestrial model: Vegetation Integrated

SImulator for Trace gases (VISIT: Inatomi et al 2010; Ito 2010). The model

consists of sub-modules simulating radiation budget, hydrology, phenology, and

carbon and nitrogen cycles. The ecosystem structure is simplified into four

sectors of carbon stock: canopy trees, floor plants, dead biomass (litter), and

mineral soil (humus). Each carbon stock sector is then divided into several

carbon pools; for example, the tree sector is composed of leaf, stem, and root

pools (see Ito et al [2005] for a schematic diagram). Photosynthetic CO2

assimilation, which is gross primary production (GPP) at the ecosystem scale, is

estimated as a function of leaf area index (LAI; estimated from the leaf carbon

pool and specific leaf area), canopy light absorption coefficient, and leaf-level

photosynthetic parameters (Ito and Oikawa 2002). Plant and soil respiration rates

are estimated from the pool-specific respiration rate, pool size, and response to

temperature. Total respiration is called ecosystem respiration (RE). Net

ecosystem production (NEP; equivalent to net CO2 exchange with the

atmosphere) is calculated as the difference between GPP and RE.

Photograph. Members of the project: Comprehensive studies of plant responses to high CO2 world by an innovative consortium of ecologists and molecular biologists.

Figure 1. Phenotypic ecophysiological parameters [PEPPs] in relation to plant CO2 response investigated by the project.

Figure 2. Scales and research targets of the project, in which consortium of molecular biology, ecophysiology, and simulation study will be formed.

Figure 3. Schematic diagram of carbon cycle in the VISIT model.

Figure 5. Scaling coefficients estimated by the optimal fingerprinting method for the carbon budget change at the Takayama site.

Figure 6 Contributions of different factors to net carbon sequestration observed at the Takayama site. Results of the mechanistic attribution on the basis of process-based model (VISIT) simulations.

Figure 4. Comparison between the observed and model-estimates CO2 fluxes.

Figure 10. Latitudinal distribution of (a) runoff discharge and (b) net primary production (NPP) of terrestrial ecosystems around 2000, as simulated by the Vegetation Integrated SImulator for Trace gases (VISIT) model. The model estimations are compared with those of Fekete et al. (2002) for runoff, who used a water-balance model (WBM) and reported a composite result based on observational data (CMP), and Cramer et al. (1999) for NPP, who used 17 terrestrial ecosystem models.

Figure 6. Summary schematic diagram of the carbon cycle and water budget of terrestrial ecosystems estimated by the VISIT model for 1995–2004.

Figure 9. Global distribution of (a) annual actual evapotranspiration (AET) and (b) annual net primary production (NPP), simulated by the VISIT model for 1995–2004.

Figure 8. Global distribution of (a) canopy-level water-use efficiency (WUEC, defined as NPP/AET) and (b) stand-level water-use efficiency (WUES, defined as GPP/TR), simulated by the VISIT model for 1995–2004.

Figure 7. Interannual variability in the global net primary production (NPP), actual evapotarnspiration (AET), and water-use efficiency (WUE) simulated by the VISIT model for 1901–2005.