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Scientific Project B3 - Influence of different pioneering plants on microbial food web development in soil during initial states of ecosystem development

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Food webs determine the functionality and stability of young ecosystems, since an efficient budget of nutrients in carbon and nitrogen limited ecosystems is the basis for the initiation and stabilisation of ecosystem processes. Therefore understanding the temporal dynamics of initial processes in the degrader’s food webs is of superior importance. The focus of this subproject is relating microbial communities in soil to the quality of exsudates respectively litter of different pioneer plants.

New findings, especially considering the integration of microbes (bacteria and fungi) into initial food webs in less structured soil ecosystems should be gained, as well as its influences on nutrient dynamics. Furthermore, in cooperation with the subprojects B1 and A3 it is to quantify the proportions of organic substances immobilised or present in the pool of dissolved organic carbon.

Different plants (Lotus corniculatus L. and Calamagrostis epigejos L.) will be pulse-labelled with ¹³CO₂ on the experimental plots to trace assimilates into stable and labile carbon pools in soil. Pulse labelling of areas without vegetation should gather information about autotrophic microbial CO₂-fixation. Further, the same plant species will be grown in a continuous ¹³CO₂-labelling atmosphere in the greenhouse to obtain labelled plant litter for experiments investigating the microbial degradation of plant litter. The identification of microbial populations is done via phospholipid fatty acid analyses (PLFA) which are an indicator for living microbial communities and rapidly degraded after cell death.
Experiments will be carried out in close cooperation with the subproject B4 to obtain a dataset about carbon and nitrogen fluxes in the rhizosphere of herbaceous and gramineous plants, as well as to get information about litter degradation kinetics in the initial phase of ecosystem development. Special attention is paid on the causal analysis of temporal dynamics and its interactions with primary producers and the soil fauna. Hence studies of this project contribute directly to the central hypotheses 1 and 3. The obtained data provide the fundament for the model of structures and processes planned by subproject C5.

Similar experiments will be carried out at the reference site Damma glacier, where litter degrading microbial communities in soil of different developmental stages in a chronosequence will be investigated by tracing ¹³C of labelled plant litter (Chrysanthemum alpinum L.) into PLFA biomarker.