Winter soil respiration during soilfreezing process in a boreal forest in Northeast China

Aims Boreal forest is the largest and contains the most soil carbon among global terrestrial biomes.Soil respiration during the prolonged winter period may play an important role in the carbon cycles in boreal forests.This study aims to explore the characteristics of winter soil respiration in the boreal forest and to show how it is regulated by environmental factors,such as soil temperature,soil moisture and snowpack.Methods Soil respiration in an old-growth larch forest(Larix gmelinii Ruppr.)in Northeast China was intensively measured during the winter soilfreezing process in 2011 using an automated soil CO_(2) flux system.The effects of soil temperature,soil moisture and thin snowpack on soil respiration and its temperature sensitivity were investigated.Important Findings Total soil respiration and heterotrophic respiration both showed a declining trend during the observation period,and no significant difference was found between soil respiration and heterotrophic respiration until the snowpack exceeded 20cm.Soil respiration was exponentially correlated with soil temperature and its temperature sensitivity(Q10 value)for the entire measurement duration was 10.5.Snow depth and soil moisture both showed positive effects on the temperature sensitivity of soil respiration.Based on the change in the Q10 value,we proposed a‘freeze–thaw critical point’hypothesis,which states that the Q10 value above freeze–thaw critical point is much higher than that below it(16.0 vs.3.5),and this was probably regulated by the abrupt change in soil water availability during the soil-freezing process.Our findings suggest interactive effects of multiple environmental factors on winter soil respiration and recommend adopting the freeze–thaw critical point to model soil respiration in a changing winter climate.