Effects of flow rate and chamber position on measurement of stem respiration rate with an open flow system in a Japanese red pine

The effects of air flow rate and chamber position on measuring stem respiration rate (Rstem) were examined using an open flow system on six Japanese red pine (Pinus densiflora Sieb. and Zucc) trees. Rstem was more closely correlated with stem temperature observed 2-6 h earlier than with current stem temperature. Rstem was not affected by the air flow rate passing through the stem chamber. Although there were no differences in stem temperatures between azimuth angles, there were significant differences in Rstem between azimuth angles (except for only one case) of each sample stem. The distance from below the bark to the stem centre varied at each azimuth in the samples, and was significantly positively correlated with R0 (p < 0.01). The chamber type did not affect the measurement of stem respiration, because the mean Rstem of four azimuth angles measured with in a rectangular chamber was almost the same as Rstem measured with in a circular chamber. From these results, we suggest that a whole circumference estimate made by either: