Do plant and soil systems contribute to global carbon cycling as a sink of CO2?

Major conclusions from our two projects focussing on carbon cycling in terrestrial ecosystems are as follows: 1) A rural system or a farmland system tends to be a source of carbon dioxide. However, it was possible 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. Nearly the same amounts of carbon as that stocked in the timbers before harvesting accumulated in 70-80 years after the cutting. 3) These results indicate the possibility of soils in terrestrial ecosystems as the major sink of atmospheric carbon dioxide.