Molecular characterization of soil organic matter along a soil chronosequence in Midtre Lovenbreen foreland in Svalbard

Abstract

Glacier forelands give an opportunity to study the successional processes in the terrestrial ecosystem along the chronosequence at a time, since the ice covers of glacier have receded over the past century. The newly exposed soil gives chances for plants and microorganisms to be established, and these organisms contribute to build up the soil organic matter (SOM) pool in this region. To investigate molecular compositions of SOM along a soil chronosequence, we took the surface soil samples at 0？5 cm depth in the glacier foreland of Midtre Lovenbreen, Svalbard in 2014. Seven sampling sites inside the moraine represented soil ages as 3, 8, 36, 57, 65, 70, and 77 years (sites 1 ？ 7, respectively). Two sites outside the moraine (sites 8, 9) were also selected as a reference. Before soil sampling, vegetation composition and coverage were surveyed. Since SOM is a mixture of materials showing various turnover time, and the content of SOM was very low in the glacier foreland, density-size based SOM fractionation was used. Firstly, sodium polytungstate solution (1.55 g cm-3) was used to separate soil into the free light fraction (FLF) which floats on the solution and the heavy fraction (HF) which sinks. Secondly, the HF was further separated as the sand-size fraction and silt and clay-size fraction based on size. Molecular composition of FLF which mostly consisting of recently added organic matter was analyzed by pyrolysis-Gas Chromatography/Mass Spectrometry (py-GC/MS) and TMAH(tetramethyl-ammonium hydroxide)-py-GC/MS at two pyrolysis temperatures (350 and 600 °C). The sand-sized and silt and clay sized fractions were treated with hydrofluoric acid to increase carbon concentration by removing mineral particles and analyzed by py-GC/MS at two temperatures (350 and 600 °C). We are currently analyzing molecular characteristics of SOM from these samples. The results of this study could provide better understanding of molecular composition of SOM, successional processes, and the relationships between SOM composition and vegetation in a newly exposed glacier foreland.