The effect of fires on the composition of aliphatic compounds in the steppe soils of Khakassia

Abstract

The aim of the study was to assess the composition of aliphaticcompoundsinsoils of post-pyrogenicterritories of the steppezone.

Location and time of the study. Soilsampleswerecollected from a depth of 0-1 cm (litter – steppe felt) and from a depth of 1-10 cm. threemonthsafter the firesat the undisturbed (control) and post-pyrogenic study sitesin the Shirinskydistrictin the vicinity of the village(southernchernozem)andin the Ust-AbakandistrictnearUst-Abakan(southernchernozem)andChernogorsk(chestnutsoil).

Methods. Organic compounds were isolated from dried and crushed soils by extraction with 7% methanol solution in chloroform. The composition of organic aliphatic compounds was determined by chromatography-mass spectrometry.

Results. Hydrocarbons (n-alkanes), saturated and unsaturated fatty acids, ketones (n-alkane-2-ones, 10-nonacosanone, 16-gentriacontanone), n-aldehydes, alcohol 1-hexacosanol were found in the composition of soil aliphatic compounds. The total content of biomolecules in the upper soil layer of the control site was on average reduced by 82% compared to the litter. Under the influence of fire, there was a sharp decrease in the amount of n-aldehydes, fatty acids, and long-chain ketones in the litter, as compared with the undisturbed sites. The distribution of n-alkanes in soils was bimodal in nature: the first mode was represented by low–molecular even homologues C₁₄–C₂₂, common in microorganisms (mainly aerobic bacteria and fungi); the second mode was represented by the high–molecular odd structures C₂₃-C₃₅, indicating the contribution of terrestrial plants in soil organic matter. In the distribution of n-alkanes of soil felts after fires, an increase in the proportion of even low molecular mass homologues was found. In comparison with the control sites, a higher content of low molecular mass homologues was also characteristic of the n-aldehydes of the most litter samples of the of burnt areas. The fire affected the steppe felt and the topsoil itself to varying degrees. The initially low soil content of biomolecules and the distribution nature of the individual homologous series in burnt areas practically did not change as compared with the control sites. Thus, under the influence of fire, certain classes of biomolecules were destroyed, primarily those containing long paraffin chains. Later on, as a result of soil microbial activity, such compounds as low-molecular even n-alkanes are additionally formed.

Conclusion. Analysis of aliphatic compounds composition in Khakassia steppe soils in the undisturbed and post-pyrogenic sites showed that biomarkers such as n-alkanes and n-aldehydes are environmental indicators of their sources, degradation processes, pyrogenic destruction and soil organic matter transformation.