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...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.展开更多
The Stefan equation provides a useful and widely used method for predicting the depth of thawing and freezing in a soil where little site-specific information is available. The original Stefan equation was derived for...The Stefan equation provides a useful and widely used method for predicting the depth of thawing and freezing in a soil where little site-specific information is available. The original Stefan equation was derived for only a homogeneous medium, and some algorithms have been developed for its use in a multilayered system. However, although the Stefan equation was derived more than 100 years ago, there is not a unified understanding for its use in a multilayered system. This paper examines the use of the Stefan equation in multilayered soil, based on comparing three algorithms(JL-algorithm, NM-algorithm, and XG-algorithm). We conclude that the JL and NM algorithms are incorrect, as they arose from flawed mathematical derivations. Both of these algorithms failed to recognize that the thawing depth in a multilayered soil is a piecewise function and not a continuous function of time. This work asserts that the XG-algorithm is a correct and rigorous method to determine the freezing–thawing fronts in multilayered soil.展开更多
基金National Natural Science Foundation of China(31021001)National Basic Research Program of China on Global Change(2010CB950600)Ministry of Science and Technology(2010DFA31290).
文摘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.
基金supported by grants from the National Natural Science Foundation of China (41671068, 41421061, and 41771040)the State Key Laboratory of Cryospheric Sciences (SKLCS-ZZ-2017)the Hundred Talents Program of the Chinese Academy of Sciences granted to Chang Wei Xie (51Y551831)
文摘The Stefan equation provides a useful and widely used method for predicting the depth of thawing and freezing in a soil where little site-specific information is available. The original Stefan equation was derived for only a homogeneous medium, and some algorithms have been developed for its use in a multilayered system. However, although the Stefan equation was derived more than 100 years ago, there is not a unified understanding for its use in a multilayered system. This paper examines the use of the Stefan equation in multilayered soil, based on comparing three algorithms(JL-algorithm, NM-algorithm, and XG-algorithm). We conclude that the JL and NM algorithms are incorrect, as they arose from flawed mathematical derivations. Both of these algorithms failed to recognize that the thawing depth in a multilayered soil is a piecewise function and not a continuous function of time. This work asserts that the XG-algorithm is a correct and rigorous method to determine the freezing–thawing fronts in multilayered soil.
