Chin J Plan Ecolo ›› 2017, Vol. 41 ›› Issue (4): 396-408.

• Orginal Article •

### Seasonality and drivers of stem CO2 efflux for four temperate coniferous tree species

Fei XU, Chuan-Kuan WANG*()

1. Center for Ecological Research, Northeast Forestry University, Harbin 150040, China
• Received:2016-05-31 Accepted:2017-04-05 Online:2017-04-10 Published:2017-05-19
• Contact: Chuan-Kuan WANG

Abstract:

Aims Stem CO2 efflux (Es) is an important component of annual carbon budget in forest ecosystems, but how biotic and environmental factors regulate seasonal and inter-specific variations in Es is poorly understood. The objectives of this study were: (1) to compare seasonal dynamics in Es for four temperate coniferous tree species in northeastern China, including Korean pine (Pinus koraiensis), Korean spruce (Picea koraiensis), Mongolian pine (Pinus sylvestris var. mongolica), and Dahurian larch (Larix gmelinii); and (2) to explore factors driving the inter-specific variability in Es during the growing and non-growing seasons.
Methods Ten to twelve trees for each tree species were sampled for Es and stem temperature at 1 cm depth beneath the bark (Ts) measurements in situ with an infrared gas analyzer (LI-6400 IRGA) and a digital thermometer, respectively, from July to October 2013 and March to July 2014. The daily stem circumference increment (Si), sapwood nitrogen concentration ([N]), and related environmental factors were monitored simultaneously.
Important findings The temporal variation in Es for the four tree species overall followed the changes in Ts throughout the study period, with the maxima occurring in the summer months (late May to early July) characterized by higher temperature and more rapid stem growth and the minima in spring (late March to April) or autumn (October) having lower temperature. Ts accounted for 42%-91% and 56%-89% of variations in Es during the growing (May to September) and non-growing (other months) seasons, respectively. Furthermore, apart from Ts, we also found significant regression relationships between Es and Si, relative air humidity and [N] during the growing season, but their forms and correlation coefficients were species-dependent. These results indicated that Ts was the dominant environmental factor affecting seasonal variations in Es, but the magnitude of the effect varied with tree species and growth rhythm. Mean Es for each of the four tree species was significantly higher in the growing season than in the non-growing season, whereas within the season there were also significant differences in mean Es among the tree species (all p < 0.05). The temperature sensitivity of Es (Q10 value) did not differ significantly among the tree species during the growing season, ranging from 1.64 for Dahurian larch to 2.09 for Mongolian pine, but did differ during the non-growing season which varied from 1.80 for Korean pine to 3.14 for Dahurian larch. Moreover, Korean spruce, Mongolian pine and Dahurian larch had significantly greater Q10 values in the non-growing season than in the growing season (p < 0.05). These findings suggested that the differences of the response of Es to temperature change for different tree species were mainly from the non-growing season. Because the seasonality and inter-specific variability in Es for these temperate coniferous tree species were primarily controlled by multiple factors such as temperature, we conclude that using a single annual temperature response curve to estimate the annual Es may lead to more uncertainty.