Cycles of Temperature and Carbon Dioxide Evolution From Litter and Soil

Periodic measurement of CO2 evolution from various biotopes reveals a daily cycle in soil respiration with a predawn minimum and an afternoon maximum that parallels the daily temperature cycle. A second maximum occasionally occurs between midnight and dawn when soil temperatures exceed temperature of the surface air. This predawn flush may result from thermal convection of CO2—rich subsurface air to the surface. The time of measurement must be considered for comparisons of rates of CO2 evolution from different sites, and measurements should be made over a 24—hr period for estimates of daily CO2 evolution.