Effects of resource quality and availability on soil microorganisms and their carbon assimilation

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During the first phase of the project we investigated how changes in resource quality, resource availability and seasonal conditions modify the bacterial and fungal contribution to organic matter decomposition and – as a consequence – to the soil food web. The importance/dominance of the fungal energy pathway was seen from an enrichment of maize derived carbon in the ergosterol fraction of up to 76.3 percent in the CM treatment. During the second phase of the project we want to follow the carbon flow separately through the herbivore and detritivore food chains under field conditions using different SIP based methods (PLFA-SIP, ergosterol-SIP and NA-SIP). We expect that carbon flow through the herbivore food chain will be faster than through the detritivore food chain. To deepen our understanding of the detritivore food web, we will perform a lab experiment using litter material of different ages. Using reciprocal transplantation of 13C and 12C maize litter on top of soil cores will allow us to follow the carbon flow into specific members of the microbial food web (bacteria, fungi, protozoa) and to calculate the turnover times of these microorganisms at different stages of maize decomposition. Data on pool size and residence time of carbon in different microbial groups are urgently needed in order to understand herbivore and detritivore food chains in agro-ecosystems.