Stem CO₂ efflux of ten species in temperate forests in northeastern China.

摘要

Stem CO₂ efflux (E_S) is an important component of forest ecosystem carbon budgets and net ecosystem CO₂ exchange, but little is known about E_S in temperate forests in Northeastern China, an area with a large extent of forest. We measured E_S 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 (E_A) and stem diameter at breast height (DBH). Our objectives were to (1) examine the seasonal patterns and species differences in E_S, and (2) determine the correlations between E_S and Ts, DBH and E_A. Mean E_S for the measurement period ranged from 1.09 to 1.74 micro mol CO₂ m-2 s-1 among the ten species. The sensitivity of E_S to Ts (Q₁₀) ranged from 1.87 to 2.61. Across the ten species 57-89% of variation in E_S was explained by T_S and DBH. There was also a linear relationship between mean E_Sand E_A. E_S 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 E_S 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, T_S, DBH and many other factors affect the relationship between CO₂ evolution by respiring cells and the diffusion of CO₂ to the stem surface.