Aims Soil respiration is an important component of terrestrial carbon budgets, but the effects of land use on soil respiration are inadequately understood. The objective of this study was to examine soil respiration in natural mixed (Betula platyphylla and Populus davidiana) secondary forest and primary Korean pine (Pinus koraiensis) forest in the Changbai Mountain, China.
Methods An infrared gas analyzer (IGA) linked to a 50 cm×50 cm×15 cm chamber without a bottom was used to measure soil respiration. Three 50 cm×50 cm steel frames were inserted into the soil to 3-5 cm in plots randomly selected one day prior to measurement. When measuring, the chamber was put on the steel frame to make a closed container capturing CO₂ from the soil surface. Soil respiration was measured every 20-30 days during the 2003-2005 growing seasons.
Important findings Diurnal variations of soil respiration were mainly affected by soil temperatures, and maximum soil respiration appeared 1-2 hours earlier in secondary than in primary forests. Soil respiration was the greatest in August. There was a significant exponential relationship with soil temperature at 5 cm depth, but no significant relationship with soil water content in both plots. During the growing season (May-September), total CO₂ efflux from natural secondary forests was estimated as 3 449.4 g·m^-2, about 1.3 times that in primary forests (2 674.4 g·m^-2). The secondary forests had higher soil temperature and lower soil water content, which enhanced roots activity and soil microorganism metabolism.