Principal Research Results

Carbon Migration in Deciduous Forest - Soil System− Carbon Storage and Soil Respiration−
Background
Forest - soil system is expected as a sink of carbon dioxide (CO2) for controlling global warming. CRIEPI (Central ResearchInstitute of Electric Power Industry) started a systematic observation for carbon fluxes and stock of organic carbon in forest - soil system in July 2001. Observation site (Kita - Saku Site) is located in Central Japan (N 36 °24 , E138° 34 , 1360~1380m a.s.l.).
Vegetation type is deciduous forest with easy gradient. Although carbon is stocked as soil organic matter in the same level with above
ground biomass, it is difficult to estimate carbon reaction in soil, and quantitative analysis method is not established. It is necessary toestablish a systematic observation method to evaluate the spatial distribution of soil respiration (CO2 efflux from soil surface) and carbon stock in soil.

Objectives(1) Development of accurate estimation method for soil respiration with spatial and seasonal variation.
(2) Evaluation of carbon storage, flux, distribution and chemistry in forest soil - atmosphere system.

Principle Results
1. Development of New Soil Respiration Observation Method(Gas Circulation Chamber)
Portable observation apparatus for daily soil respiration was developed (Fig.1). In foregone apparatus, it is difficult to control CO2 concentration in an observation chamber. The new circulation chamber is able to observe soil respiration actually by synchronize CO2 concentration in the chamber with ambient concentration. Based on this new apparatus results, foregone method results andsoil temperature, soil respiration estimation method at a low cost and accuracy was developed.
2. Soil Respiration in Observation Site
Base on statistical analysis about spatial variation of observed CO2 respiration, optimum arrangement of observation points
for accurate evaluation in an observed area was proposed. Using this method and observed soil temperature, annual respiration in KitaSaku site was estimated as 6-7t C/ha/yr (Fig.2, May 2001 - Apr 2003).
3. Chemistry and Distribution of Soil Organic Carbon
Vertical distribution and chemistry of soil organic carbon (SOC), which is a source of soil respiration, was analyzed in Kita saku site. SOC with 34 t C/ha was observed in layer between ground surface and 20cm depth. This storage was about 30-40% of carbon storage in forest - soil system. The most labile component in SOC was distributed in the layer upper than 15cm depth. SOC with
1.1 t C/ha was decomposed annually and released to atmosphere. On the other hand, runoff of carbon with leakage of soilwater wasnegligible.

Future Developments
Development of prediction method for SOC storage in future by enlarged applicability of soil organic matter models toJapanese mountainous forest soil.
Main Researchers:
Hideshi Ikeda, Ph. D., Research Engineer, and Shinji Yasuike, Ph. D., Research Scientists, Geospheric and Hydrospheric Environment
Sector, Environment Science Research Laboratory
Reference
Yasuike, S. et al,:Development of an evaluation method for spatial distribution of soil-CO2 efflux in forest sites. CRIEPI Report :U03010 (2003, September, in Japanese)
Ikeda H. et al., :Migration and Fixation of Organic Carbon in Vegetation - Forest soil System, Geochimica et Cosmochimica Acta,67(18S), 2003.p A167.

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C. Harmonization of energy and environmentFig.1 Schematic diagram of gas circulation chamber

1614121086420May
JunJulAug
Sep
Oct
Nov
Dec
JanFebMar
AprMayJunJulAug
Sep
Oct
Nov
Dec
JanFebMar
AprSoil respiration (gCO2/m2/day)

An on/off flow controller connected with the air pump keeps the CO 2 concentration in thechamber at a set value. The mechanism enables the precise measurement of CO2 efflux from soil
surface (Jap. Pat. JP2001-296215A)

Date (2001-2003)

Fig.2 Seasonal change of soil respiration measured by gascirculation chamber (from May 2001 to Apr. 2003)

Soil respiration highly depends on soil temperature andconsequently the value increased during the summer
season and decreased during winter.

Fig.3 Depth Profile of SOC

More than 50% of SOC is observed in layer 20cm
depth. It shows seasonal variation; high in summer
and low in winter.

AtmosphereVegetation
Biomass
60〜 70

Soil Respiration
6.0〜7.0
Throughfall
0.1

Litterfall
1.4

Ground Surface
Soil Organic Carbon 34.0
Annual Increase
0.3

Release from root
Decay of death root

CO2 in Soil Air
Decay ofOrganic Carbon

5.0〜6.0Leakage with Soilwate

1.10.1

RiverSoil・Soilwater： Flux as Solid： Liquid： GaseousFig.4 Storage and Annual Carbon Flux in Forest−Soil System (t C/ha, August 2001〜July 2002)

Organic carbon, 1.4 t C/ha annually, was supplied as litterfall. Carbon was distributed to 0.3 t
C/ha as storage in soil, and 1.1 t C/ha as decay in soil. Decayed organic carbon and released CO2
from root are sources of soil respiration (6.0〜7.0 t C/ha).

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