Abstract: In this paper,soil respiration chamber,a simple and precise method,was used to measure the stem respiration of trees.LI-6400-09 respiration chamber serving as a system is usually used in soil respiration,but we made polyvinyl chloride (PVC) collar and fixed it on the stem surface to measure the stem respiration.From May to October 2003,the stem respiration of Pinus koraiensis, the dominant tree species in Changbai Mountain,was measured in different time and different places using this technique.Meanwhile,the temperatures in the stems and in the forests were measured.The results showed that the stem respiration rate had a remarkably seasonal tendency with a single peak,the maximum was in August and the minimum was in February.The stem respiration rate had an exponential relationship with stem temperature,and the curve exponential regressions for stem respiration rate and temperature factor of trees with big DBH were better than those with small DBH.The stem respiration in different DBH trees was higher in the south stem face than that in the north stem face,and the variance of respiration rate between south and north decreased with a decrease of DBH trees. During the growing season from May to October,the average maintenance respiration accounted for 63.63% in different DBH trees,and the maintenance respiration contribution to total respiratory consumption increased with increasing DBH,which was 66.76,73.29% and 50.84%, respectively. The tem respirationQ₁₀ values ranged from 2.56～3.32 in different DBH of trees,and the seasonal tendency for stem R_t and R_m in different DBH of trees was obtained by using respiration Q₁₀.Therefore,the differences between different parts of stem and different DBH of trees should be considered in estimating the respiration model in ecosystem.

Key words: Dinoflagellate cyst, Changjiang River estuary, Red tide