Impact of expected global warming on C mineralization in maritime Antarctic soils: results of laboratory experiments

Abstract

This study concerned the fragility of maritime Antarctic soils under increasing temperature, using the C dynamics and structural characteristics of humic substances as indicators. Working with four representative soils from King George Island (Lithic Thiomorphic Cryosol (LTC1 and LTC2), Ornithogenic Cryosol (OG) and Gelic Organosol (ORG)) we evaluated the total organic C and nitrogen contents, the oxidizable C and humic substances. Soil samples were incubated to assess the amount of C potentially mineralizable at temperatures typical of an Antarctic summer (5-148C). Humic acids showed a higher aliphatic character and a smaller number of condensed aromatic groups, which suggests that these molecules from Antarctic soils are generally less resistant to microbial degradation than humic acids molecules from other regions. Based on 13 C NMR spectra of MAS and CP/MAS, samples of soil humic acids of mineral soils (LTC1 and LTC2) have a higher content of aliphatic C, and heteroatom C, with lower levels of carbonyl and aromatic C, when compared with organic matter-rich soils (OG and ORG). Increasing incubation temperature led to a higher rate of mineralizable C in all soils. A sequence of soil fragility was suggested -LTC1 and LTC2 . OG . ORG -which showed a correlation with the Q10 coefficient and the ratio of labile and recalcitrant C fractions of soil organic matter (R 2 5 0.83).

Microbial response to warming and cellulose addition in a maritime Antarctic soil

“…This could cause decomposition rates to be higher 8,9 than expected since SOC litter is mainly composed of C derived from cellulose, lipids, and peptides, although incipient humic substances have also been isolated from these soils 10–12 . These results are consistent with studies using cross‐polarization magic angle spinning (CPMAS), nuclear magnetic resonance for C ( 13 C‐NMR), nitrogen ( 15 N‐NMR) spectroscopy, and pyrolysis field‐ionization mass spectrometry (Py‐FIMS) for organic histosols formed from mosses on the Antarctic continental coast in Eastern Antarctica 11,12 and soils formed under similar conditions in Western Antarctica, King George Island 13,14 . Previous research on SOC composition in these environments found carbohydrates and the enrichment of alkyl‐C and showed signals of incipient formation of aromatic structures due to the scarce presence of vascular plants and the lack of lignin, in mosses and lichens 12,13 .…”

“…pyrolysis field-ionization mass spectrometry (Py-FIMS) for organic histosols formed from mosses on the Antarctic continental coast in Eastern Antarctica 11,12 and soils formed under similar conditions in Western Antarctica, King George Island. 13,14 Previous research on SOC composition in these environments found carbohydrates and the enrichment of alkyl-C and showed signals of incipient formation of aromatic structures due to the scarce presence of vascular plants and the lack of lignin, in mosses and lichens. 12,13 Therefore, increasing temperatures in Maritime Antarctic soils may cause fast turnover of SOC because readily decomposable organic C has not been extensively mineralized due to cold conditions and the absence of recalcitrant organic compounds.…”