Soil organic matter and the extracellular microbial matrix show contrasting responses to C and N availability

摘要: An emerging paradigm in soil science suggests microbes can perform ‘N mining’ from recalcitrant organic matter (SOM) conditions of low N availability. However, this requires the production extracellular structures rich (including enzymes and structural components) thus defies stoichiometric expectation. We set out to extract newly synthesised peptides matrix compare amino acid (AA) profiles, incorporation AA dynamics response labile inputs contrasting C/N ratio. Glycerol was added both with without an inorganic source (10% 15N labelled NH4NO3) a already containing large pool refractory SOM incubated for 10 days. The resulting total peptide (TSP) pools were compared using colorimetric methods, gas chromatography, isotope ratio mass spectrometry. compositions showed that polymeric substance (EPS) contained greater proportion products formed de novo than did TSP, hydrophobic EPS-AAs (leucine, isoleucine, phenylalanine, hydroxyproline tyrosine) deriving substantially more provided. Quantitative comparison between extracts EPS relative proportions alanine, glycine, proline, phenylalanine tyrosine. greatest increases EPS-peptide EPS-polysaccharide concentrations occurred at highest ratios. All responded similarly treatment whereas responses TSP complex. results suggest investment (as peptides) is microbial survival mechanism N/high C which, evolutionary perspective, must ultimately lead tendency increased returns biomass. A conceptual model proposed describes inputs.