Autor:innen:
Ubaida Yousaf | Trier University | Germany
Denise Vonhoegen | Trier University | Germany
Prof. Dr. Sören Thiele-Bruhn | Trier University | Germany
Soil microbes play a significant role in the formation and turnover of soil organic matter (SOM). Thus, OM is metabolized by microorganisms, with one portion of it being converted into biomass and another being respired for energy. This causes an energy and matter flux that is adjusted and slowed down by ongoing recycling of the matter and residual energy. This is realized in energy use channels, resulting in biomass growth and/or necromass formation. To comprehend C turnover and sequestration in terrestrial ecosystems, further knowledge of the relationship between element cycling and energy fluxes is required. In this project, we present a conceptual overview of microorganisms as mediators of SOM production, by investigating carbon substrates with varying complexity with the same model soil (farmyard manure fertilized Luvisol; long-term fertilization experiment Dikopshof, Bonn, Germany). We investigated the effect of substrate size (Glucose — 180 Da, α-1,4-maltotetraose — 666,6 Da, starch — 325 kDa) and substrate rigidity (Starch — α-1,4 glycosidic bonds vs. cellulose —β-1,4). For the first part, we hypothesize that exoenzymes would be required to degrade any substrate greater in size than 600 Da, meaning different carbon use efficiency CUE, and thus also energy use efficiency, due to a change in the process type from growth-oriented processes — high energy flux for glucose degradation to the adaptation-oriented processes (interlinkage of energy flux networks within the system) for the larger substrate, i.e., maltotetraose and starch in this case. For the second part, we hypothesize that chemical stability impacts degradation kinetics and CUE, favouring adaptation-oriented processes. The substrates were labelled with 13C to balance the turnover, identify the carbon in the functional pools, and determine kinetics. Incubation experiments were time-resolved samples and gas flux sampling and isotope selective CO2 analysis were done. Elemental analysis of C, H, N, S, O, and P was done to calculate the stoichiometry of OM. Chloroform fumigation extraction was performed to determine microbial biomass carbon and nitrogen. In combination with further data the microbial quotient (Cmic/OC), the respiratory quotient (qCO2=resp./Cmic), and CUE were calculated. Aminosugars and acids were used as markers of microbial biomass/necromass. This enabled the estimation of carbon and energy accumulation in the form of additional biomass, necromass, and metabolites.