Organic carbon and carbon isotopes in modern and 100‐year‐old‐soil archives of the Russian steppe
Organic carbon and carbon isotopes in modern and 100‐year‐old‐soil archives of the Russian steppe
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DOI：
10.1046/j.1365-2486.2002.00477.x
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发表时间：
2002-10
影响因子：
11.6
通讯作者：
M. Torn;A. Lapenis;A. Timofeev;M. Fischer;B. Babikov;J. Harden
中科院分区：
文献类型：
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作者：
M. Torn;A. Lapenis;A. Timofeev;M. Fischer;B. Babikov;J. Harden
存档土壤可以提供有关过去一个世纪土壤碳和碳同位素含量变化的有价值的信息。我们利用一个100年前的土壤档案和从同一地点收集的现代样本，对俄罗斯草原保护区的土壤碳动态进行了表征。从1885年到现在，该遗址一直受到保护，在此期间，该地区经历了广泛的耕作，火灾频率减少，降雨量有增加的趋势。在保护区内，在1900至1997年的采样日期之间，有机碳的数量没有明显的变化，最高的米为32公斤C/平方米，最高的20厘米为三分之一。在两个复制的现代土坑之间，或者在现代遗址和档案馆之间，碳和氮储量的差异不到6%。所有地点的放射性碳含量都随着深度的增加而下降，由于20世纪60年代初的核武器试验，现代土壤有机质在表层附近具有正的Δ值。在表层10 cm处，大多数有机质的周转时间为6-10年，符合放射性碳含量的模型。在10 cm以下，有机质几乎都是被动物质，周转时间较长(千年)。夏日土壤呼吸Δ~(14)CO_2为10~6-10~9‰，与大气~(14)CO_2的同位素不平衡约为9‰。在现代土壤和归档土壤中，有机质中13C的相对丰度随着深度的增加而增加2‰，从5 cm处的δ13C=-26‰到1米以下的-24‰。此外，在5 cm以下，两种土壤的δ13C斜率与深度的关系是相同的。考虑到土壤档案的年代，这些结果提供了明确的证据，表明深度梯度不是由于化石燃料排放消耗大气13CO2，而是由植物凋落物输入和SOM保存之间的同位素分馏造成的。总体而言，数据显示，这些土壤中有大量顽固性碳的储存库，而且在相隔100年的采样日期之间，储量没有变化。
Archived soils can provide valuable information about changes in the carbon and carbon isotope content of soils during the past century. We characterized soil carbon dynamics in a Russian steppe preserve using a 100‐year‐old‐soil archive and modern samples collected from the same site. The site has been protected since 1885 to the present, during which time the region has experienced widespread conversion to cultivation, a decrease in fire frequency, and a trend of increasing precipitation. In the preserve, the amount of organic carbon did not change appreciably between the 1900 and 1997 sampling dates, with 32 kg C/m2 in the top meter and a third of that in the top 20 cm. Carbon and nitrogen stocks varied by less than 6% between two replicate modern soil pits or between the modern sites and the archive. Radiocarbon content decreased with depth in all sites and the modern SOM had positive Δ values near the surface due to nuclear weapons testing in the early 1960s. In the upper 10 cm, most of the SOM had a turnover time of 6–10 years, according to a model fit to the radiocarbon content. Below about 10 cm, the organic matter was almost all passive material with long (millennial) turnover times. Soil respiration Δ14CO2 on a summer day was 106–109‰, an isotopic disequilibrium of about 9‰ relative to atmospheric 14CO2. In both the modern and archive soil, the relative abundance of 13C in organic matter increased with depth by 2‰ in the upper meter from δ13C = ‐‐26‰ at 5 cm to ‐‐24‰ below a meter. In addition, the slope of δ13C vs. depth below 5 cm was the same for both soils. Given the age of the soil archive, these results give clear evidence that the depth gradients are not due to depletion of atmospheric 13CO2 by fossil fuel emissions but must instead be caused by isotopic fractionation between plant litter inputs and preservation of SOM. Overall, the data show that these soils have a large reservoir of recalcitrant C and stocks had not changed between sampling dates 100 years apart.