Accumulation of aliphatic compounds in soil with increasing mean annual temperature

Chemical recalcitrance of biomolecules, physical protection by soil minerals and spatial inaccessibility to decomposer organisms are hypothesized to be primary controls on soil organic matter (SOM) turnover. Previous studies have observed increased sequestration of plant derived aliphatic compounds in experimentally warmed soils but did not identify the mechanisms for this enhanced preservation. To further test the role of environmental conditions in the preservation of aliphatic carbon, we analyzed native soils along a bicontinental, longitudinal, mean annual temperature (MAT) gradient to examine relationships between SOM composition, soil physical properties and temperature. Using biomarker analysis by gas chromatography-mass spectrometry and solid state 13C nuclear magnetic resonance to characterize SOM, we observed that the concentration of aliphatic compounds derived from the waxes and cuticles of plant leaves increased with MAT. We did not observe any significant correlations between aliphatic SOM and clay mineral content which suggests that their inherent chemical recalcitrance is responsible for their persistence in soils. Other SOM components were not correlated with MAT, indicating that temperature alone does not control the overall preservation and biodegradation of soil carbon. As such, other environmental factors (e.g., microbial community structure and activity, litter quality and quantity, mineral surfaces, soil moisture content and antioxidant capacity) also play a role in the selective preservation or accumulation of various SOM components. However, our study shows that the accumulation of aliphatic SOM components is highly correlated to MAT.