Stem CO2 efflux of ten species in temperate forests in Northeastern China

Stem CO2 efflux (ES) is an important component of forest ecosystem carbon budgets and net ecosystem CO2 exchange, but little is known about ES in temperate forests in Northeastern China, an area with a large extent of forest. We measured ES along with stem temperature at 1 cm depth (Ts) over a 9 month period in 2007 on ten dominant tree species of secondary forests of the region. Other measurements included the autotrophic component of soil CO2 efflux (EA) and stem diameter at breast height (DBH). Our objectives were to (1) examine the seasonal patterns and species differences in ES, and (2) determine the correlations between ES and Ts, DBH and EA. Mean ES for the measurement period ranged from 1.09 to 1.74 μmol CO2 m−2 s−1 among the ten species. The sensitivity of ES to Ts (Q10) ranged from 1.87 to 2.61. Across the ten species 57–89% of variation in ES was explained by TS and DBH. There was also a linear relationship between mean ES and EA. ES was better predicted by Ts in the dormant season than the growing season, indicating that additional factors such as growth respiration and internal transport of CO2 in the xylem became more important contributors to ES during the growing season. Stem CO2 efflux increased, and Q10 decreased, with increasing DBH in all species. Although temperature exerts strong control on the rate of cellular respiration, we conclude that in tree stems in situ, TS, DBH and many other factors affect the relationship between CO2 evolution by respiring cells and the diffusion of CO2 to the stem surface.