DIURNAL VARIATIONS OF SOIL TRACE GASES AND RELATED IMPACTING FACTORS
土壤温室气体昼夜变化及其环境影响因素研究

Diurnal variations of concentrations and surface fluxes of soil CO 2, N 2O, and CH 4, and soil temperatures at an untilled grassland site and a forest site in the Donglingshan, Beijing during the summer were introduced, and possible impacting factors were discussed in this paper. (1) The surface emission flux of soil CO 2 is large in day time and low in night time. The surface emission flux of soil N 2O fluctuates on an hourly scale not a semidiurnal scale. The fluctuation of soil CO 2 and N 2O concentrations is also on an hourly scale not a semidiurnal scale, and different from the fluctuation of their surface emission flux. Soil absorbs atmospheric CH 4 and is a sink for CH 4. (2) During the rainless period, the semidiurnal fluctuation of air temperature influences the surface fluxes of soil CO 2 and N 2O by affecting the gas diffusion process and soil CO 2-producing process in topsoils above 10 cm. There may be other factors or mechanisms inducing hourly-scaled variations of soil CO 2 and N 2O concentrations. (3) During the rainy period, soil seep-water leads air convection in soil that replaces the gas diffusion to be the major air-exchange manner between soil and atmosphere, resulting in the synchronal change of surface emission fluxes of soil CO 2 and N 2O. When rainwater dissolved more oxygen seeps into soil, more soil CO 2 is produced. (4) The soil CO 2 concentration is positively correlative with the soil N 2O concentration, demonstrating that their production ratio is relatively stable in soils. Soil available carbon (as dissolved organic carbon, DOC) may be an important factor resulting in the positive correlation between soil CO 2 and N 2O concentrations. The change of the oxygen concentration in soil air may lead the difference between fluctuations of soil CO 2 and N 2O concentrations.