Use of ¹³C-labelled plant materials and ergosterol, PLFA and NLFA analyses to investigate organic matter decomposition in Antarctic soil

The relationship between organic matter decomposition and changes in microbial community structure were investigated in Antarctic soils using ¹³C-labelled plant materials. Soils with and without labelled Deschampsia antarctica (a native Antarctic grass) were incubated for 42 days and sampled at 0, 7, 14, 21, 28 and 42 days. Changes in microbial community structure were assessed using phospholipid fatty acid analysis (PLFA) and an analysis of the fatty acids associated with the neutral lipid fraction (NLFA). These studies showed that there were no significant changes in PLFA or NLFA profiles over time suggesting no change in microbial community structure during residue decomposition. There was a marked increase however, in ergosterol levels in these soils indicative of growth of the fungal biomass. Analysis of this ergosterol using gas chromatography-mass spectrometry confirmed the transformation of the plant residue by showing the incorporation of ¹³C-plant C into the ergosterol. This incorporation of ¹³C into the ergosterol increased over the incubation period. Importantly, these changes associated with fungal growth were not evident in the analysis of either the PLFA or NLFA fractions thus questioning the reliability of such approaches for studying changes in microbial communities associated with the decomposition of plant residues.