BayCEER Workshop 2019
October 10, 2019
NW III, University of Bayreuth
Long-term stabilization of labile carbon in soil microbial biomass and its residues – A question of microbial nitrogen demand?
2 Department of Forest Sciences, University of Helsinki
3 Department of Geosciences and Natural Resource Management, University of Copenhagen
4 Biogeochemistry Research Group, University of Eastern Finland
5 Department of Soil Biogeochemistry, Martin-Luther-University Halle-Wittenberg
O 2.2 in Stable isotopes in environmental research - bridging disciplines, organisms and processes
10.10.2019, 14:45-15:00, H36, NW III
It was assumed for a long time that soil organic carbon (SOC) storage is mainly regulated by non-biological soil properties and by selective preservation of recalcitrant compounds. Yet, a new paradigm points to a more active role of microorganisms in regulating C storage. In this context, even labile C may persist for a long time due to micr. transformation into compounds that become stabilized. However, there is little knowledge about the fate of labile C in soil and its regulating factors. We assume that this is mainly driven by nitrogen (N) demand. We hypothesize that high N demand forces microbes to decompose N-rich micr. residues, leading to their rapid turnover, but that labile C is stabilized in micr. residues when N demand is met.
We use a stable isotope approach to investigate these hypotheses. Trace amounts of 13C labeled glucose were added to soil, which allows following the fate of labile C. This was conducted in a greenhouse including four treatments: (1) bare soil, (2) bare soil+N, (3) tree, and (4) tree+N. The soil is a sandy and nutrient poor Podzol from Finland. Trees are 1 m high pines, which are supposed to induce micr. N deficiency by exuding C and by competing with microbes for mineral N. The treatments were replicated 4 times with 13C-glucose and 12C-glucose, each. We sampled the soil regularly throughout one year. Measurements of 13C recovery in bulk soil, micr. biomass, water extractable C, amino sugars, and DNA are in progress.
First results indicate that largest loss of 13C tracer indeed occurred in the unfertilized tree treatment, i.e., where N demand was high but N supply was low. Here, the recovery was 20% after 3 month, whereas 40% remained in the fertilized tree treatment. Only small proportions of 13C were present in the pool of water extractable C and in living micr. biomass. As fixation by clay minerals in unlikely in this sandy soil, we suspect the remaining 13C to be stabilized in microbial residues, but depending on N demand.
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