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Yields and Characterization of Dissolved Organic Matter From Different Aged Soils in Northern Alaska
Author(s) -
Gao Lei,
Zhou Zhengzhen,
Reyes Alberto V.,
Guo Laodong
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2018jg004408
Subject(s) - dissolved organic carbon , environmental chemistry , chemistry , soil water , total organic carbon , organic matter , soil organic matter , phosphorus , nitrogen , humus , environmental science , soil science , organic chemistry
Soil organic matter (SOM) in northern high‐latitude regions is a major component of the global carbon cycle. However, the yield of soil‐dissolved organic matter (DOM) during soil‐water interactions and its chemical characteristics and reactivities remain poorly understood. We report here elemental composition and isotopic signatures of bulk‐SOM from northern Alaska, and yields of water‐leachable soil‐DOM, including dissolved organic carbon, dissolved organic nitrogen, and dissolved organic phosphorus, and nutrients (dissolved inorganic nitrogen and phosphate). The bulk‐SOM contained 5,400–373,900 μg‐C/g‐soil, 500–12,610 μg‐N/g‐soil, and 38.6–384 μg‐P/g‐soil, with a C/N ratio of 13–37 and a C/P ratio of 80–3,911. The water‐extractable dissolved organic carbon, dissolved organic nitrogen, and dissolved organic phosphorus only accounted for 0.58–2.5%, 0.91–3.4%, and 1.2–3.0% of their corresponding total soil‐OC, N, and OP, respectively. While SOM‐δ 13 C was less variable (−27.08‰ to −26.49‰) showing the same overall C source, 14 C‐ages varied widely from 1,170 ± 20 to 16,200 ± 55 years before present, indicating different deposition‐conditions and subsequent‐processes among the soil samples. The specific‐UV‐absorbance at 254 nm (or aromaticity) of soil‐DOM differed considerably and was negatively correlated to spectral slope values. A humic‐like (C1), a low‐molecular‐weight fulvic‐like (C2), and a protein‐like component (C3) were identified as the major fluorescent‐DOM components. The C3/C2 and C3/C1 ratios generally increased with SOM‐ 14 C‐age, suggesting a preferential degradation/transformation of humic‐like and fulvic‐like components or a transformation/production of protein‐like components within permafrost. Both biological and humification indices increased with 14 C‐age, excluding the oldest soil, which pointed to a preferential preservation or transformation/production of protein‐like DOM within permafrost, implying that soil‐DOM derived from old permafrost can be highly vulnerable and readily decomposed upon permafrost thaw.