Chemical composition of soil organic matter and potential enzyme activity in the topsoil along a moisture gradient in the High Arctic (Svalbard)

Abstract The soil active layer in the High Arctic is a reservoir for nutrients and microbial communities, but their behavior and interactions remain unclear. Therefore, the objective of this study was to characterize soil organic matter (SOM) composition and potential enzyme activities in soil active layer of Svalbard. Samples from two different sites and two different soil layers (biocrust: 0–1 cm; mineral soil: 5–10 cm depth) were collected along a moisture gradient. The molecular SOM composition was assessed using pyrolysis-field ionization mass spectrometry (Py-FIMS), and the potential activities of seven extracellular enzymes characteristic for different soil microbial processes were measured. In general, SOM in both sites was dominated by lipids/sterols, alkylaromatics and phenols/lignin monomers. Dehydroergosterol prevailed in a majority of the samples. Biocrusts samples in both sites had higher total ion intensity and volatile matter, but lower lipid and alkylaromatics contents. The potential enzyme activities varied significantly across the sites, depths and moisture gradients and, in general, were higher in the biocrusts than in underlying soils. Besides, majority of measured enzyme activities were lower in the wetter plots. Taken together, our results expand the knowledge of SOM and enzyme activity in High Arctic topsoil, which is important for better understanding the dynamic of soil biotic and abiotic processes in polar environments, particularly in the context of climate change.