比较利用静态箱式法测定长白山原始阔叶红松林(Pinus koraiensis)和次生杨桦混交林的土壤呼吸作用表明，两者土壤呼吸作用的日动态均主要受温度影响，次生林土壤呼吸作用的日变化极值出现时间较原始林提前1～2 h；两者具有明显的季节动态，其中8月土壤呼吸速率最大；在生长季，土壤呼吸速率与土壤含水量关系不显著，而与土壤5 cm温度呈显著的指数关系；生长季(5～9月)次生林土壤释放CO2量(3 449.4 g·m－2)约为原始林(2 674.4 g·m－2)的1.3倍，这可能是由于次生林内具有比原始林较高的温度和较低的土壤含水量，更有利于根系生长代谢和土壤微生物的活动引起的。
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.