Interactions between root C, microbial activity and turnover, and food web complexity

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Microbial activity is the key parameter of turnover of microbial biomass and of soil organic matter (SOM) and it strongly depends on the availability of rhizodeposits and litter as the primary carbon (C) sources. Beside respiration, other microbial activity parameters were never linked with the turnover of microorganisms and of SOM. In this project we challenge to link microbial and SOM turnover estimated by δ13C after C3/C4 vegetation change and by 13C/14C labeling experiments with 20 parameters of microbial activity such as substrate limited and unlimited respiration, maximal and real specific growth rates, substrate affinity and mineralization potential, activities of enzymes. Time and depth gradients will be used in the ongoing and new wheat/maize field experiments for evaluation of root effects on microbial activity parameters and δ13 C based turnover of microbial C and SOM over long periods (months to years). The effects of root-C on short-term turnover and activity parameters will be evaluated comparing rhizosphere and bulk soil in new experiments. In model studies focused on binary links, multitrophic interactions and microbial loop the microbial activity parameters will be linked with complexity and abundance of microbial grazers. These data will be used for modeling of C fluxes within the soil food web and microbial turnover depending on grazing intensity. Finally we will suggest microbial activity proxies adequately reflecting microbial turnover.