Abstract: The mountainous areas of eastern Liaoning Province have a long and cold winter with deep snow cover. At the beginning and end of the nongrowing season in late autumn and early spring, however, topsoil undergoes repeated freezethaw cycles and soil CO₂ emission during these periods can be important in annual carbon budget. In this study, we set up three 20 m × 30 m plots in a Korean larch (Larix olgensis Henry) plantation, a common forest type in eastern Liaoning Province, and measured soil respiration (R_s) to quantify CO₂ emission (F_CO2) during the periods of freezethaw cycles in late autumn and early spring. Four polyvinyl chloride (PVC) collars were installed in each plot and R_s was measured, 2-3 times a month for 4 winters (2010-2014), using portable CO₂ infrared gas analyzer (Li-8100). The results showed a “U” change of R_s in nongrowing season from late autumn to early spring. R_s was positively correlated with soil temperature at 10 cm depth (T₁₀) and air temperature (T_a) and the relationship was best fitted with an exponential model. The fitted relationships were stronger in late autumn than in early spring and in 2010/2011 and 2011/2012 winters than in 2012/2013 and 2013/2014 winters. R_s varied substantially among years from (0.42±0.02) to (0.72±0.04)  μmol CO₂·m^-2·s^-1 by nongrowing season averages and the total F_CO2 in nongrowing season was 137, 92, 100 and 159 g C·m^-2 for the 4 study winters, respectively. Within a nongrowing season, the F_CO2 in late autumn ranged from 29.66 to 63.48 g C·m^-2 in the 4 years, about 0.68-3.36 times greater than that in early spring. The overall contribution of F_CO2 in the two freezethaw periods in late autumn and early spring to the total F_CO2 in the nongrowing season ranged from 47.69% to 54.66% across the 4 study winters. The acceleration capacity of soil CO₂ release of freezethaw cycles during the alternation of autumn to winter was stronger than that during alternation of winter to spring. These results help understand the patterns of forest soil carbon emission during non-growing season in northeastern China.

Key words: Torreya grandis ‘Merrillii’, cultivation history, microbial diversity, Illumina sequencing, rhizosphere soil