Microbial enzyme activities and use channels during microbial turnover of organic carbon substrates in soil

Recent studies of soil organic matter formation focus on energy and matter fluxes and their linkage to broaden the understanding of the processes and drivers underlying microbial turnover of organic carbon substrates in soil. In this study, which is part of the DriverPool project in the SoilSystems priority program, the energy and mass balances of organic matter turnover are investigated with special reference to the soil microbial community by testing selected hydrocarbon substrates with different properties.

In a first incubation experiment the effect of substrate size was investigated by comparing the turnover of glucose (180 Da) and α-1,4-maltoteraose (666.6 Da). We hypothesize that exoenzymatic activity is required for substrates exceeding a size of 600 Da; thus, resulting in a different process type (adaptation-oriented process) compared to the intracellular turnover of  glucose (growth-oriented process). From a batch microcosm experiment, subsamples were collected after different incubation periods to determine microbial pools (biomass, necromass) and the incorporation of the C¹³-labeled substrates. Enzymatic activity of exoenzymes (α- and β-glucosidase, N-acetyl-glucosaminidase, sulfatase, phosphatase, fungal peroxidase) and endoenzymatic activity (dehydrogenase) were assessed to elaborate the understanding of metabolic pathways. To analyze shifts in the microbial community and to identify a bacterial- or fungal-dominated use channel for each substrate, substrate induced alteration in phospholipid fatty acid (PLFA) patterns of the harvested samples will be studied as well. First results show differences in enzyme activity pattern for glucose and maltotetraose.