Aims: We investigated the role of plants and their plant-derived carbon in shaping the microbial community that decomposes substrates and traced the return of nutrients from decomposition back to plant shoots in order to understand the importance of plants for ecosystem element cycling. Methods: We performed a greenhouse experiment having plant communities with and without arbuscular mycorrhizal fungi (AMF) and ingrowth cores that held different 15N labeled substrates. We determined the microbial community structure using molecular sequencing and the net assimilation of plant carbon into soil microorganisms using a 13CO2 pulse and 13C measurements of microbial biomarkers. We determined the return of nitrogen back to the shoots using the 15N signal, which was provided from the decomposition of the substrate added to the ingrowth cores. Results: We observed that the microbial community composition in the ingrowth cores and their net 13C assimilation depended on the presence of AMF and the added substrate. Both plant communities had similar 15N uptake into their shoots, but the net N uptake cost was significantly lower in presence of AMF. In the presence of AMF also lower net N uptake cost was observed for the decomposition of plant-derived and microorganism-derived substrates compared to inorganic nitrogen suggesting that AMF actively controls the decomposer comunity and their carbon demand. Conclusion: Our results identify for the first time a functional overlap of soil microorganisms as identical substrate is decomposed by different microorganisms suggesting functional redundancy of microbial communities. In consequence a better understanding of ecosystem element cycling can only be achieved when the whole plant-microorganism-organic matter-soil continuum is investigated.
SC received funding from long term DAAD scholarship to carry out the research. ML is funded by the German Research Foundation (DFG; FOR 456, FOR 1451 – “The Jena Experiment”) and by the “Zwillenberg-Tietz Stiftung”. We acknowledge help from Agnes Fastnacht with greenhouse resources and monitoring of the experiment. Special thanks to Karl Kübler for construction and deployment of the pulse labelling setup in the greenhouse. We acknowledge Heike Geilmann and Steffen Ruehlow for help with stable isotope measurements, and Maria Foerster for helping with fatty acid analysis. We also thank Erika Kothe, Ruchira Mukherji, Elisa Catao and Huei Ying Gan for helpful comments and discussions and Simon Benk for proof reading the MS.
Open Access funding enabled and organized by Projekt DEAL.
- 16S rRNA Gene
- Functional redundancy
- Ingrowth core
- Pulse labeling