Abstract
Abstract. Despite the importance of soil organic matter (SOM) in the global carbon cycle, there remain many open questions regarding its formation and preservation. The study of individual organic compound classes that make up SOM, such as lipid biomarkers including n-alkanes, can provide insight into the cycling of bulk SOM. While studies of lipid biomarkers, particularly n-alkanes, have increased in number in the past few decades, only a limited number have focused on the transformation of these compounds following deposition in soil archives. We performed a systematic review to consolidate the available information on plant-derived n-alkanes and their transformation from plant to soil. Our major findings were (1) a nearly ubiquitous trend of decreased total concentration of n-alkanes either with time in litterbag experiments or with depth in open plant–soil systems and (2) preferential degradation of odd-chain length and shorter chain length n-alkanes represented by a decrease in either carbon preference index (CPI) or odd-over-even predominance (OEP) with depth, indicating degradation of the n-alkane signal or a shift in vegetation composition over time. The review also highlighted a lack of data transparency and standardization across studies of lipid biomarkers, making analysis and synthesis of published data time-consuming and difficult. We recommend that the community move towards more uniform and systematic reporting of biomarker data. Furthermore, as the number of studies examining the complete leaf–litter–soil continuum is very limited as well as unevenly distributed over geographical regions, climate zones, and soil types, future data collection should focus on underrepresented areas as well as quantifying the transformation of n-alkanes through the complete continuum from plant to soil.
Highlights
Soil organic matter (SOM) is one of the largest terrestrial reservoirs in the carbon cycle, containing a carbon stock more than 10 times greater than that of forest biomass (Settele et al, 2015)
Prior to incorporation in soil, plant debris can form a litter layer on top of the soil, especially in forest ecosystems. This plant debris is the principal source of material for the formation of soil organic matter in the topsoil (Kögel-Knabner, 2002), and degradation of plant-derived n-alkanes begins in the litter layer
We found a total of six litterbag experiment studies during the review ranging in time intervals from 300 d to 23 years (Table 1)
Summary
Soil organic matter (SOM) is one of the largest terrestrial reservoirs in the carbon cycle, containing a carbon stock more than 10 times greater than that of forest biomass (Settele et al, 2015). In the last few decades, there has been a myriad of studies using lipids in soil as molecular proxies for a variety of purposes, including paleoecology and paleoclimate reconstructions (Jansen and Wiesenberg, 2017). Many of these compounds are considered “biological markers”, or “biomarkers” for short, because they can be indicative of their source organisms and may be preserved following deposition in environmental archives, such as soils and sediments (Peters et al, 2005). Many of these compounds are considered “biological markers”, or “biomarkers” for short, because they can be indicative of their source organisms and may be preserved following deposition in environmental archives, such as soils and sediments (Peters et al, 2005). n-Alkanes, in particular, have been used extensively
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