Kurganova Irina, Teepe Robert, Loftfield Norman
Institute of Physicochemical and Biological Problems in Soil Science, Russian Academy of Sciences, Pushchino, Moscow region, 142290, Russia.
Carbon Balance Manag. 2007 Feb 19;2:2. doi: 10.1186/1750-0680-2-2.
The repeated freeze-thaw events during cold season, freezing of soils in autumn and thawing in spring are typical for the tundra, boreal, and temperate soils. The thawing of soils during winter-summer transitions induces the release of decomposable organic carbon and acceleration of soil respiration. The winter-spring fluxes of CO2 from permanently and seasonally frozen soils are essential part of annual carbon budget varying from 5 to 50%. The mechanisms of the freeze-thaw activation are not absolutely clear and need clarifying. We investigated the effect of repeated freezing-thawing events on CO2 emission from intact arable and forest soils (Luvisols, loamy silt; Central Germany) at different moisture (65% and 100% of WHC).
Due to the measurement of the CO2 flux in two hours intervals, the dynamics of CO2 emission during freezing-thawing events was described in a detailed way. At +10 degrees C (initial level) in soils investigated, carbon dioxide emission varied between 7.4 to 43.8 mg C m-2h-1 depending on land use and moisture. CO2 flux from the totally frozen soil never reached zero and amounted to 5 to 20% of the initial level, indicating that microbial community was still active at -5 degrees C. Significant burst of CO2 emission (1.2-1.7-fold increase depending on moisture and land use) was observed during thawing. There was close linear correlation between CO2 emission and soil temperature (R2 = 0.86-0.97, P < 0.001).
Our investigations showed that soil moisture and land use governed the initial rate of soil respiration, duration of freezing and thawing of soil, pattern of CO2 dynamics and extra CO2 fluxes. As a rule, the emissions of CO2 induced by freezing-thawing were more significant in dry soils and during the first freezing-thawing cycle (FTC). The acceleration of CO2 emission was caused by different processes: the liberation of nutrients upon the soil freezing, biological activity occurring in unfrozen water films, and respiration of cold-adapted microflora.
在寒冷季节，反复的冻融事件，即秋季土壤冻结和春季土壤解冻，是冻原、北方和温带土壤的典型特征。冬夏过渡期间土壤解冻会导致可分解有机碳的释放和土壤呼吸的加速。永久冻土和季节性冻土在冬春季节的二氧化碳通量是年碳预算的重要组成部分，占比从5%到50%不等。冻融激活的机制尚不完全清楚，需要进一步阐明。我们研究了在不同湿度（田间持水量的65%和100%）下，反复冻融事件对完整耕地和森林土壤（灰化土，壤质粉砂；德国中部）二氧化碳排放的影响。
由于每两小时测量一次二氧化碳通量，详细描述了冻融事件期间二氧化碳排放的动态变化。在所研究的土壤中，在+10℃（初始水平）时，根据土地利用类型和湿度，二氧化碳排放量在7.4至43.8毫克碳每平方米每小时之间变化。完全冻结土壤的二氧化碳通量从未达到零，相当于初始水平的5%至20%，这表明微生物群落在-5℃时仍具有活性。在解冻过程中观察到二氧化碳排放显著激增（根据湿度和土地利用类型增加1.2至1.7倍）。二氧化碳排放与土壤温度之间存在密切的线性关系（R2 = 0.86 - 0.97，P < 0.001）。
我们的研究表明，土壤湿度和土地利用类型决定了土壤呼吸的初始速率、土壤冻结和解冻的持续时间、二氧化碳动态变化模式以及额外的二氧化碳通量。通常，冻融引起的二氧化碳排放在干燥土壤和第一个冻融循环（FTC）期间更为显著。二氧化碳排放的加速是由不同过程引起的：土壤冻结时养分的释放、未冻结水膜中发生的生物活动以及适应寒冷的微生物群落的呼吸作用。
