DO PLANT AND SOIL SYSTEMS CONTRIBUTE TO GLOBAL CARBON CYCLING AS A SINK OF CO2 - EXPERIENCES FROM RESEARCH PROJECTS IN JAPAN

Major conclusions from our two projects focussing on carbon cycling in terrestrial ecosystems are as follows: 1) A rural system or a farmlan d system tends to be a source of carbon dioxide. However, it was possi ble to increase carbon dioxide sequestration in soil by changing soil or paddy/upland-field management systems. 2) A model simulation showed that a carbon budget in a natural forest was balanced before cutting but the large minus (source) was observed just after cutting. But the balance changed from minus to plus (sink) in 10 years after cutting. N early the same amounts of carbon as that stocked in the timbers before harvesting accumulated in 70-80 years after the cutting. 3) These res ults indicate the possibility of soils in terrestrial ecosystems as th e major sink of atmospheric carbon dioxide.