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).