ABSTRACT
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 Concept of Carbon Cycle in Agroecosystems . . . . . . . . . . . . . . . . . . . . . . . . 208 Carbon Fixed and Respired by Crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 Soil Respiration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
East Asian Monsoon Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 Northern Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 Soil Respiration in Agricultural and Natural Ecosystems . . . . . . . . 217
CO2 Released from the Snow Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 Net Ecosystem Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
East Asian Monsoon Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 Northern Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Mitigation Potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
INTRODUCTION
Since the increased emission of greenhouse gases, especially carbon dioxide, into the atmosphere may become a serious environmental problem in the world, quantitative studies on the carbon cycle are essential to predict the CO2-induced warming effect on the earth. The carbon cycle in a terrestrial ecosystem involves the circulation of carbon among the atmosphere, vegetation, and soil as carbon pools. Of these carbon pools, soil is the largest reservoir (1500 Pg on a global scale, or twice the atmospheric carbon pool; Watson et al., 1990). Therefore, relevant discussions about the carbon cycle require
information on the carbon flux between soil and the atmosphere or between soil and vegetation.
