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

Background/Question/Methods

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 forests. We conducted E_S measurements over a 9-month period in 2007 on ten dominant tree species of secondary forests of the region: Mongolian oak (Quercus mongolica), Amur linden (Tilia amurensis), aspen (Populus davidiana), white birch (Betula platyphylla), Manchurian ash (Fraxinus mandshurica), Manchurian walnut (Juglans mandshurica), maple (Acer mono), elm (Ulmus propinqua), Dahurian larch (Larix gmelinii), and Korean pine (Pinus koraiensis). Using the mature tissue approach, we separated E_S into maintenance (E_M) and growth components.  E_S at a common temperature (15^oC; E₁₅) was also calculated.  Other measurements included stem temperature at the surface and 1 cm depth, soil moisture, stem diameter, and mean annual growth increment. Our specific objectives were to: (1) quantify annual E_S and its relation to mean annual growth increment and tree size; and (2) examine seasonal patterns in E_S and correlated environmental factors.

Results/Conclusions

E_S was strongly positively correlated to stem temperature at 1 cm depth (Ts) and stem diameter in 8 of the 10 species measured. E_M was also positively correlated with stem diameter. There was also a linear relationship between mean E_S and mean annual increment.  There was a significant interaction of Ts and stem diameter on E_S in 3 species, Dahurian larch, Mongolian oak and elm. The sensitivity of E_S to Ts (Q₁₀) ranged from 1.87 for Manchurian ash to 2.61 for aspen. Although Q₁₀ varied among species, it did not vary with diameter class. The Q₁₀ of trees in large, medium, and small diameter classes ranged from 1.86 to 3.12, 1.97 to 2.89 and 1.79 to 2.60 within each diameter class, respectively.  Seven of the species showed no change in E₁₅ over time, indicating a lack of acclimation to seasonal changes in temperature. Mean efflux of the deciduous species were slightly higher than those of the coniferous species. We conclude that E_S can be accurately predicted for most of these species from measurements of stem temperature and stem diameter.  However, a few of the species will require further study to determine why they were exceptions to this pattern.