MICDIF – Linking MICrobial DIversity and Function
I did my master thesis in the MICDIF Project at the University of Vienna, Austria. More specifically, I was part of the MICDIF 07 subproject “Microbial processes and functional community structure”. For my master thesis, I developped a new isotope pool dilution (IPD) assay to determine the breakdown of starch and cellulose during the early decomposition stages of leaf litter.
To this end, we incubated 4 beech litter types that differed in litter chemistry and elemental composition (C:N:P ratio) for 6 months in the lab. For my IPD assay, I added 13C-labelled glucose to the litter and measured how both concentration and 13C-signature changed over the course of 3 hours. This enabled me to calculate gross rates of glucose production through enzymatic depolymerization of the glucans starch and cellulose, and glucose consumption by the microbial community.
Gross rates of glucan depolymerization and glucose consumption were highly correlated, indicating that both processes are co-regulated and intrinsically linked by the microbial demand for C and energy. In fresh litter (2 weeks old), microorganisms predominantly decomposed starch as C-supply. In older litter (3 to 6 months), after depletion of starch, microorganisms switch to cellulose breakdown. At this stage, glucan depolymerization was promoted by high N concentrations of the litter, which indicates that microorganisms preferably decompose cellulose when they have excess-N (i.e. when they are C-limited).
Mooshammer M, Hofhansl F, Frank AH, Wanek W, Hämmerle I, Leitner S, Schnecker J, Wild B, Watzka M, Keiblinger KM, Zechmeister-Boltenstern S, Richter A (2017): Decoupling of microbial carbon, nitrogen, and phosphorus cycling in response to extreme temperature events. Science Advances, 3, e1602781.
Leitner S, Wanek W, Wild B, Hämmerle I, Keiblinger KM, Zechmeister-Boltenstern S and A Richter (2012): Influence of litter chemistry and stoichiometry on glucan depolymerization during decomposition of beech (Fagus sylvatica L.) litter. Soil Biology & Biochemistry, 50, 174-187.
Keiblinger KM, Schneider T, Roschitzki B, Schmid E, Eberl L, Hämmerle I, Leitner S, Richter A, Wanek W, Riedel K and S Zechmeister-Boltenstern (2012): Effects of stoichiometry and temperature perturbations on beech litter decomposition, enzyme activities and protein expression. Biogeosciences, 9, 4537-4551.
Mooshammer M, Wanek W, Schnecker J, Wild B, Leitner S, Hofhansl F, Blöchl A, Hämmerle I, Frank AH, Fuchslueger L, Keiblinger KM, Zechmeister-Boltenstern S and A Richter (2012): Stoichiometric controls of nitrogen and phosphorus cycling in decomposing beech leaf litter. Ecology, 93(4), 770–782.
Leitner S: Influence of litter chemistry and stoichiometry on glucan depolymerisation during decomposition of beech (Fagus sylvatica) litter. University of Vienna, 2010.