Our main research subjects in FY 1996 were (1) climate change and variability of agricultural production in East Asia, (2) gas flux measurements of CH4 and CO2 in the Arctic tundra of Alaska, Kushiro wetland in Hokkaido and rice paddies in Okayama, and (3) development of a rice growth model for a cool-weather damage forecast. We had three themes under the Bilateral International Joint Research program with special coordination funds from the Science and Technology Agency entitled “Accurate evaluation and modeling of methane at the Arctic Tundra ecosystem ”, and “Gas flux measurement at rice paddies by use of Inverse Lagrangian technique”. Thus, we are taking the lead in international collaboration researches in our institute.
Topic1
Net Primary Productivity and its Seasonal Variation under the Doubled CO2 Concentration in Japan
The increasing CO2 concentration in the atmosphere and the accompanying global warming due to human activities are predicted to have enormous effects on crop productions in the future.The net primary productivity of natural vegetation affected by the global warming was evaluated, using the climate change scenarios derived from three general circulation models (GCMs) of the Geophysical Fluid Dynamic Laboratory (GFDL),the Goddard Institute for Space Studies (GISS) and the United Kingdom Meteorological Office (UKMO).
The annual values of the net primary productivity increased in the whole of Japan under the doubled CO2 concentration. In the summer season,when most natural plants are growing, the net primary productivity increased by about 20% compared with now in Tohoku and Hokkaido districts because of the direct beneficial effects of CO2, where summer mean temperature increased by 4-C simulated by GFDL. On the contrary, the net primary productivity decreased by 15 to 20% in Tokai and Chugoku districts, and the southern part of Shikoku (Fig.1), where summer mean temperature increased up to 3.5-C of the present. This was because the direct beneficial effects of CO2 could not compensate for the remarkable decrease in net primary productivity due to more active plant respiration and the higher temperature stresses.
Topic2
Micrometeorological measurements of trace gas fluxes in various ecosystems
In order to reveal the contribution of terrestrial ecosystems on global change, we have been measuring trace gas flux under natural conditions using micro-meteorological methods.We improved the flux evaluation techniques,and developed a NDIR (Non-Dispersive Infra-Red) -CH4 analyzer to continuously measure CH4 flux. We applied these techniques to various ecosystems such as the Japanese rice paddy field, Kushiro mire, and Alaskan Tundra (Fig.2). From our field studies,CH4 flux was determined as 30-370 mg CH4 m-2 d-1 in flooded rice field during cultivation periods, around 200 mg CH4 m-2 d-1 at Kushiro mire in mid-summer, and 10-60 mg CH4 m-2 d-1 in Alaskan moist tundra with seasonal variations (Fig.3). Furthermore we found sink CH4 flux of 30-60 mg CH4 m-2 h-1 in dry grassland in Japan. Field studies are now continuing in various ecosystems. These results obtained under natural conditions are very valuable for the global inventory studies and useful for parameterization in Global Circulation Model studies.
Topic3
Absorption of CH4 and CO by Soil
The atmospheric concentrations of CH4 and CO have been increasing rapidly after the industrial revolution. The role of the agro-ecosystem is extremely important for controlling the concentrations of these gases.
CH4 and CO were absorbed by soil microorganisms, and the vertical profiles of CH4 and CO concentrations showed positive gradients (Fig.4). The gradient of CO was greater than that of CH4. Our measurements at NIAES by chamber methods showed that CH4 downward flux and CO destruction velocity ranged from 0 to 0.06µg m-2s-1 and from 0 to 0.08cm s-1, respectively. CH4 absorption depended not only on the soil temperature but also on the gas-filled porosity of the surface soil. CO absorption was mainly controlled by the gas-filled porosity of the surface soil.
Fig.1 The spatial distribution of net primary productivity during summer season under the doubled CO2 concentration compared with the present, evaluated using the climate change scenarios derived from the Geophysical Fluid Dynamic Laboratory's model.
Fig.2 View of meadow tundra observation site at Happy Valley, Alaska in June,1995.
The equipment shown at the center is an eddy correlation system with open path IRGA and sonic anemometer,
the tower at the LHS is used to measure micro-meteorology such as wind speed, temperature, gas concentration profiles.
Fig.3 Intra-seasonal trends in CO2 flux and CH4 flux measured over the Arctic moist tundra at Sagavanirktok,
Alaska in 1996.
CO2 flux was determined by EC and CH4 flux using an improved gradient method with a NDIR-CH4 analyzer.
Fig.4 Soil atmospheric concentrations of a) CH4 and b) CO.
The samples were taken at an upland field in NIAES during the summer of 1995.